f.4 acids and exercise)
TRANSCRIPT
EXERCISE A :
1. 07/I/5.
A solid sample contains zinc and copper only. The composition of the solid sample was analysed experimentally as outlined below :
2.00 g of the solid sample was added to excess dilute hydrochloric acid in a beaker. Upon completion of reaction, the mixture inside the beaker was filtered. The residue obtained was first washed with distilled water, and then dried. The mass of the dried residue was 1.75 g.
(a) Write a chemical equation for the reaction involved. (1 mark)
(b) How can one know that the reaction has been completed. (1 mark)
(c) Explain why it is necessary to wash the residue obtained. (1 mark)
(d) Explain why it is NOT appropriate to dry the residue with a Bunsen flame after washing. (1 mark)
(e) Assuming negligible experimental errors, calculate the percentage of zinc by mass in the solid sample. (2 marks)
SOLUTION :
(a) Zn + 2HCl ZnCl2 + H2 1
(b) No further gas evolved. 1
(c) to wash away Zn2+ /H+ left behind 1
(d) copper will be oxidized 1
(e) % of zinc by mass in the sample(2.00 – 1.75) / 2.00 100 %= 12.5 2
2. 07/I/10.
In an experiment to determine the concentration of phosphoric acid (H3PO4), 10.0 cm3 of the acid was first diluted to 250.0 cm3 with distilled water. 25.0 cm3 of the distilled solution was then transferred to a conical flask and titrated with a 0.025M sodium hydroxide solution using phenolphthalein as indicator. 17.6 cm3 of sodium hydroxide solution was needed to reach the end point.
(a) Describe briefly how 10.0 cm3of phosphoric acid can be diluted to 250.0 cm3with distilled water in the laboratory. (2 marks)
(b) Phosphoric acid reacts with sodium hydroxide in the titration according to the following equation :H3PO4 + 2NaOH Na2HPO4 + 2H2O
Calculate the molarity of the original phosphoric acid before dilution. (3 marks)
(c) ‘At the beginning of titration, the solution in the conical flask turned pink upon the addition of sodium hydroxide but become colourless immediately upon swirling. However, near the end-point, the solution took longer time to become colourless upon swirling.’Explain why the time needed for the solution to become colourless is different at the two stages mentioned above. (2 marks)
(d) In the titration, the 0.025 M sodium hydroxide solution was used as a standard solution.(i) What does the term ‘ standard solution mean’ ?(ii) Comment whether it is appropriate to prepare a standard solution of sodium hydroxide by the
following procedure :‘Weigh a sample of solid sodium hydroxide, dissolve it in some distilled water and make up to a known volume of solution.’
(2 marks)
SOLUTION :
(a) 10.0 cm3 of the acid is transferred into a 250 cm3 volumetric flask using a pipette 1Distilled water is added up to graduation mark 1
(b) no. of moles of NaOH = 0.0176 0.025 = 4.4 10-4
no. of moles of H3PO4 in 25 cm3 of the diluted solution = 4.4 10-4 / 2 = 2.2 10-4
molarity of the original phosphoric acid = 2.2 10-4 10 / (10/1000) = 0.22M3
(c) neutralization is a quick process 1As titration proceeds, concentration of acid decreases, less chance of NaOH to contact with
the acid 1
(d) (i) a solution with known concentration 1
(ii) not appropriate, solid sodium hydroxide absorbs water in air. 1
3. 06/I/3.(b)
Concentrated sulphuric acid can be used as a toilet bowl cleaner. However, many toilet bowl cleaners contain granular sodium hydrogensulphate (NaHSO4) as the active ingredient instead of concentrated sulphuric acid.(i) Write the chemical equation for the formation of sodium hydrogensulphate from sulphuric acid.(ii) State ONE advantage of using granular sodium hydrogensulphate over using concentrated
sulphuric acid as a toilet bowl cleaner.(2 marks)
SOLUTION :
(i) NaOH + H2SO4 NaHSO4 + H2O 1Or Na2O + 2H2SO4 2NaHSO4 + H2O
(ii) Conc. H2SO4 is strongly corrosive. 1Or Conc. H2SO4 readily absorbs water vapour but NaHSO4 is not, so it can be kept for a longer
time.Or Conc. H2SO4 can damage drainage pipes but NaHSO4 will not.
4. 06/I/7.
The following two methods can be used to convert copper metal into copper(II) nitrate solution :
Method 1 : Cu(s) CuO(s) Cu(NO3)2(aq)
Method 2 : Cu(s) Cu(NO3)2(aq)
(a) Refer to Method 1.(i) Suggest how copper metal can be converted into copper(II) oxide. State the expected
observation in the reaction that you have suggested.(ii) Name the type of reaction that occurs between copper(II) oxide and dilute nitric acid.
(3 marks)(b) In method 2, the reaction of copper metal with dilute nitric acid gives copper(II) nitrate,
nitrogen monoxide and water. Write the chemical equation for this reaction.(2 marks)
(c) Which of these methods would you recommend for the conversion of copper metal into copper(II) nitrate solution ? Justify your answer with TWO reasons.
(2 marks)
SOLUTION :
(a) (i) heat copper in air 1
dilute HNO3(aq)
dilute HNO3(aq)
Reddish brown copper changes into black copper(II) oxide 1(ii) neutralization 1
(b) 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO 1+1Or 3Cu + 8H+ + 2NO3
- 3Cu2+ + 4H2O + 2NO
(c) open-ended question
Method 1 : - less reactant is used 1 - method 2 gives toxic product (NO) but method 1 does not - in method 2, NO reacts with O2 in air to give NO2 which causes acid rain
Method 2 : - the conversion involves one step 1 only1 - in method 1, copper and oxygen do not easily undergo complete reaction - in method 1, more energy is required
5. 06/I/9.
‘Soda ash’ is crude sodium carbonate (Na2CO3) commonly used in treating fresh water in water treatment plants. The following experiment was carried out to determine the percentage by mass of sodium carbonate in a sample of soda ash :
2.00 g of the sample was dissolved in distilled water, and the solution was diluted and made up to 250.0 cm3. Four portions of the diluted solution of volume 25.0 cm3 each were titrated against 0.18 M hydrochloric acid using methyl orange as indicator. The table below lists the titration results obtained :
Titration Burette reading
1 2 3 4
Final reading / cm3 21.00 21.10 25.20 25.20
Initial reading / cm3 0.00 1.00 5.30 5.20
(a) A 25.0 cm3 portion of the above diluted solution was transferred to a clean conical flask. Briefly describe how the titration of this portion of the diluted solution should be carried out.
(3 marks)
(b) Based on the titration results, calculate
(i) a reasonable average for the volume of the hydrochloric acid used, and (ii) the percentage by mass of sodium carbonate in the sample.(You may assume that the sample does NOT contain any impurity that reacts with hydrochloric acid.)
(5 marks)
(c) Suggest another method for detecting the titration end point without the use of any acid-base
indicator.(1 mark)
(d) Why is soda ash used for treating fresh water ? Briefly describe the chemistry involved.(2 marks)
SOLUTION :
(a) Use a burette to contain HCI(aq). 1Rinse the burette with distilled water (deionised water) and then with the 0.18 M hydrochloric acid. 1
or, Fill the burette with the cid and ensure that no air is trapped in the burette.or, Record burette reading before and after the titration.or, Add acid to Na2CO3(aq) while swirling the conical flask. Add the acid dropwise
until the end point is reached.
Add the indicator to the flask, and then the acid from the burette until the indicator changes from yellow to orange (red) / changes colour. 1(1 mark for using a burette; 1 mark for one step of the titration; 1 mark for colour change at end-point.)
(b) (i) 1/3(20.10+19.90+20.00) = 20.00 cm3 1(ii) CO3
2- + 2H+ → CO2 + H2ONo. of moles of H+(aq) used = 0.18 20 10-3
= 3.6 10-3 No. of moles of Na2CO3 in 25.0 cm3 of diluted solution
= 3.6 10-3 1/2 1No. of moles of Na2CO3 in 2g of the sample
= 3.6 10-3 10/2 1 = 0.018
Mass of Na2CO3 = 0.018 (23 2 + 12 + 16 3) 1 = 1.908 g
% by mass of Na2CO3 in the sample = 1.908 1/2 100%= 95.4 % 1
(c) Use a pH meter / pH sensor 1or, Conduct a thermometric titration / conductometric titration
(d) Na2CO3 is used to remove hardness (Mg2+ / Ca2+) in fresh water. 1
Mg2+ or Ca2+ ions in hard water react with CO32- to form insoluble metal carbonates /
precipitate 1
or, Na2CO3 is used to remove acidity.Fresh water after treated with chlorine is slightly acidic. Na2CO3 can neutralize the acid formed.
6. 06/I/12.
You are provided with the following materials :
Magnesium ribbon and 2 M hydrochloric acid
Design an experiment to determine the molar volume of hydrogen at room temperature and pressure.(You may use apparatus commonly available in school laboratory.)
(9 marks)
SOLUTION :
Description of procedure (4M)Remove oxide layer on Mg ribbon 1Weigh the piece of Mg ribbon in grams (w) 1Put Mg ribbon in a conical flask connected to a gas syringe 1Add 2M HCl to Mg ribbon until in excess 1Collect hydrogen gas liberated by the syringeMeasure the volume of hydrogen gas collected (v)
Treatment of data (2M)
Mg + 2H+ → Mg2+ + H2 1Or 1 mol of Mg gives 1 mol of H2
Molar volume of H2 = molar mass of Mg (cm3)
or molar mass of Mg 1/1000(dm3) 1
E.C. = 3 M
7. 05/I/3.
A student proposed the following methods to accomplish three tasks, (a), (b) and (c). The proposed methods were all considered inappropriate.
(a) Task : To neutralize acidic soil in a flower bed.Proposed method : Add solid sodium hydroxide to soil.
(i) State ONE reason why the method is inappropriate.(ii) Suggest an appropriate method to accomplish.
(2 marks)
(b) Task : To prepare hydrogen gas from an acid.Proposed method : Add copper to dilute hydrochloric acid.
(i) State ONE reason why the method is inappropriate.
(ii) Suggest an appropriate method to accomplish.(2 marks)
(c) Task : To dilute concentrated sulphuric acid with water.Proposed method : Add water to concentrated sulphuric acid and stir the mixture.
(i) State ONE reason why the method is inappropriate.(ii) Suggest an appropriate method to accomplish.
(2 marks)
SOLUTION :
(a) (i) NaOH is a strong alkaline. It will damage the plants. 1 (ii) Aadd CaCO3 or Ca(OH)2. 1
(b) (i) There is no reaction between copper and dil. HCl. 1 (ii) Add a more reactive metal such as Zn or Mg. 1
(c) (i) Adding water into conc. H2SO4 is highly exothermic, acid will be splashed out. 1 (ii) conc. H2SO4 should be added slowly into a large amount of water with constant
stirring. 1
8. 05/I/10.
The information below was found on the label of effervescent vitamin C tablets :
(a) With the help of a chemical equation, explain why effervescence occurs when a tablet of the effervescent vitamin C is added to water.
(b) An experiment was carried out to study the action of water on a tablet of the effervescent vitamin C using the set-up as shown below. The graph shows the results obtained in the experiment.
Each tablet contains 1000 mg of vitamin C.
Other ingredients : sodium hydrogencarbonate, citric acid, sugar and colourant
(b) (i) Find, from the graph, the mass of gas liberated from the reaction of the tablet with water. (You may assume that the gas liberated is NOT soluble in water.)
(ii) At the end of the experiment, the sodium hydrogencarbonate in the tablet had been completely used up. Calculate the mass of sodium hydrogencarbonate present in the tablet.
(iii) Suggest ONE advantage of using a data-logger in this experiment.
(iv) The experiment was repeated using warm water instead of cold water. Sketch, on the same graph, the results that would be obtained in the repeated experiment.
(6 marks)
SOLUTION :
(a) when the tablet is added into water, citric acid will ionize in water to give H+, which will react with HCO3
- to form CO2 and water. H+ + CO3
2- CO2 + H2O 1
(b) (i) 168.235 – 168.137 = 0.098 g 1 (ii) no. of moles of CO2 = 0.098/12+162 = 2.27 10-3 1 no. of moles of CO2 = no. of moles of HCO3
2- = 2.27 10-3
mass of HCO32- = 2.27 10-3 (23 + 1 + 16 3)
= 0.187 g 1
(iii) change of mass can be determined monitored continuously. 1
(iv)
19. 04/I/7.(a)
An experiment, consisting of the three stages listed below, was carried out to determine the basicity of a solid acid :
Stage 1 : 1.15 g of a sample of the acid was weighed.Stage 2 : The sample of acid was dissolved in some distilled water and then made up to
250.0 cm3 with distilled water.Stage 3 : 25.0 cm3 of the solution obtained in stage 2 was titrated against 0.100 M sodium
hydroxide solution using phenolphthalein as indicator. 25.7 cm3 of the sodium hydroxide solution was required to reach the end point.
(i) Briefly describe how the 250.0 cm3 solution was made up in stage 2.(ii) State the colour change at the end point of the titration in stage 3.(iii) (1) Calculate the number of moles of sodium hydroxide used in the titration. (2) Given that the molar mass of the solid acid is 90.0 g. Calculate its basicity.
(8 marks)
SOLUTION :
(i) Transfer the solution in a 250.0 cm3 volumetric flask. 1Add distilled water to the flask until the bottom of the meniscus reaches the mark of the flask. 1
(ii) From colourless to pink. 1
(iii) (1) no. of moles of NaOH = 0.1 25.7 10-3 = 2.57 10-3 1 (2) no. of moles of ionisable hydrogen in 1.15 g of solid acid = 10 25.7 10-3
= 2.57 10-3 1
cold water
warm water
Mass of conical flask and its content / g
Time / s
No. of moles of acid used = 1.15/90 1
Basicity of acid = = 2.01
1 n = 2 1
10. 04/I/7.(c)(i)
State what would be observed in the following experiment and explain your answer.
A beaker containing some concentrated sulphuric acid was left in the air for a long period of time.
(2 marks)
SOLUTION :
The mass of the beaker and its contents increases. / the volume of liquid in the beaker increases.1
Conc. H2SO4 absorbs water from the atmosphere. 1
11. 04/I/8. (a)
Coral consists mainly of calcium carbonate. An experiment was carried out to determine the percentage by mass of calcium carbonate in a sample of coral using the set-up below :
(i) Write a chemical equation for the reaction of calcium carbonate with dilute hydrochloric acid.
(ii) The mass of the sample used was 0.36 g. At the end of the experiment, 78 cm3 of carbon dioxide was collected at room temperature and pressure.
Calculate (1) the number of moles of carbon dioxide collected, and (2) the percentage by mass of calcium carbonate in the sample.
Excess dilute hydrochloric acid
gas syringe
coral
(iii) Assuming that there was no leakage of gas in the set-up, suggest ONE source of error in the experiment.
(molar volume of gas at room temperature and pressure = 24.0 dm3; relative atomic masses : C = 12.0, O = 16.0, Ca = 40.0)
(7 marks)
SOLUTION :
(i) CaCO3 + 2HCl CaCl2 + CO2 + H2O 1
(ii) (1) no. of moles of CO2 = 78/24000 1= 3.25 10-3 1
(2) no. of moles of CaCO3 = 3.25 10-3
Mass of CaCO3 in the sample = 3.25 10-3 100 = 0.325 g 1 % by mass of CaCO3 = 0.325/0.36 1
= 90.27 1
(iii) some CO2 dissolves in water 1
12 . 03/I/8.(b)
An experiment was carried out to determine the concentration of a nickel(II) sulphate solution. The experiment consisted of the following three stages :
Stage 1 : 25.0 cm3 of 0.503 M sodium hydroxide solution was added to 25.0 cm3 of the nickel(II) sulphate solution to precipitate out nickel(II) hydroxide.
Stage 2 : The mixture obtained in stage 1 was filtered and the residue was washed thoroughly with distilled water.
Stage 3 : The excess alkali in the filtrate was titrated against 0.251 M hydrochloric acid with methyl orange as indicator. 18.5 cm3 of the acid was required to reach the end-point.
(i) Write the ionic equation for the reaction in Stage 1.
(ii) State the colour change at the end-point of the titration in stage 3.
(iii) (1) Based on the titration result in Stage 3, calculate the number of moles of hydroxide ions
present in the filtrate. (2) Calculate the number of moles of sodium hydroxide that was added in Stage 1. (3) Using your results in (1) and (2) above, calculate the molarity of the nickel(II) sulphate
solution.
(iv) Why was it necessary to wash the residue thoroughly in Stage 2 ?
(9 marks)
SOLUTION :
(i) Ni2+ + 2OH- Ni(OH)2 1
(ii) yellow to orange 1
(iii) (1) H+ + OH- H2O 1 1 mole of H+ reacts with 1 mole of OH-
no. of moles of OH- in the filtrate = 0.251 18.5 10-3
= 4.64 10-3 1
(2) no. of moles of NaOH used = 0.503 25 10-3
= 0.0126 1
(3) No. of NaOH that has reacted with Ni2+
= 0.012575 – 4.6435 10-3
= 7.96 10-3 1 Ni2+ + 2OH- Ni(OH)2
Conc. of Ni2+ =
1 = 0.158 M 1
(iv) To remove OH- ions which have adhered to the surface of the residue. 1
13 . 02/I/9.
(a) Ammonia is a weak alkali. It is used as an active ingredient in domestic glass cleaners.
(i) (1) Write a chemical equation to represent the ionization of ammonia in water.(2) Explain why an alkaline solution can help remove oily dirt on glass.
(ii) Suggest, with explanation, a precaution necessary when using such glass cleaners.(4 marks)
(b) In the experiment to determent the concentration of ammonia in a sample of glass cleaner, 25.0 cm3 of the sample was diluted to 250.0 cm3 in a volumetric flask. 25.0 cm3 of the diluted sample was transferred to a conical flask and was then titrated against 0.23 M hydrochloric acid. 28.7 cm3 of the acid was required to reach the end-point.
(i) State the liquid that should be used to rinse the following pieces of apparatus used in this experiment.(1) Volumetric flask (2) Conical flask
(ii) Name the apparatus that should be used to transfer 25.0 cm3 of the diluted sample to the conical flask.
(iii) Calculate the concentration, in mol dm-3 , of ammonia in the sample of glass cleaner.
(You may assume that ammonia is the only substance in the sample that reacts with hydrochloric acid.)( 6 marks )
SOLUTION :
(a) (i) (1). NH3 + H2O NH4+ + OH- 1
(2). Alkaline solution reacts with oil to form soaps which is water soluble. 1
(ii) Wear gloves as alkaline solution is corrosive / 1,1Use the glass cleaner in a well-ventilated room as NH3 is toxic.
(b) (i) (1). Distilled water. 1(2). Distilled water. 1
(ii) *Pipette. 1
(iii) No. of mole of HCl used = 0.23
No. of mole of HCl used = 6.6 10-3 1
NH3 + HCl NH4+ + Cl-
No. of mole of NH3 in 25 cm3 solution = No. of mole of HCl = 6.6 10-3
No. of mole of NH3 in 250 cm3 solution
=6.6 10-3 1
= 6.6 10-2
Conc. of NH3 = 6.6 10-2
Conc.H3 = 2.64 mol dm-3 1
14 . 01/I/2(b)
For each of the following experiments, state an expected observation and write a chemical equation for the reaction involved.
Adding sodium hydroxide solution to iron(II) sulphate solution
(2 marks)
SOLUTION :
Green precipitate is formed. 1Fe2+ + 2OH- Fe(OH)2 1
15 . 01/I/6.(b)
In an experiment, 0.933 g of a sample of washing soda (Na2CO3.xH2O) was dissolved in some distilled water. The solution was titrated against 0.258 M hydrochloric acid with methly orange as indicator. 25.4 cm3 of the acid was required for the complettion of the following reaction :
Na2CO3 + 2HCl 2NaCl + H2O + CO2
(i) From the titration result, calculate the number of moles of sodium carbonate in the sample of washing soda.
(ii) Describe the value of x in the formula of the washing soda.(iii) State the colour change at the end-point of the titration.(iv) Briefly describe the procedure that should be followed to prepare a burette containing the hydrochloric acid for the titration.(Relative atomic masses : H = 1.0, C = 12.0, O = 16.0, Na = 23.0)
(9 marks)
SOLUTION :
(i) no. of moles of HCl used = 0.258 25.4 10-3 = 6.55 10-3 1 no. of moles of Na2CO3 = 6.55 10-3 2
= 0.0328 1
(ii) Formula mass of Na2CO3.xH2O = 23 2 + 12 + 16 3 + 18 x 1
no. of moles of Na2CO3.xH2O =
0.00328 = 1
x = 10 1
(iii) from yellow to orange 1(iv) rinse the burette with distilled water 1then with HCl 1fill the burette with the HCl, making sure that the space between the tap and the tip of the burette is filled with the acid / there is no air bubble in the burette / the burette is clamped in a vertical position.
1
16 . 00/I/4. (Essay)
The mass of a sample of copper powder contaminated with copper(II) oxide is known. Describe how you would conduct an experiment to determine the percentage by mass of copper powder in the sample. State the expected observation of the experiment.(Hint : You may use an acid in the experiment.)
(9marks)
SOLUTION :
Chemical knowledge (6 marks)
Add excess dilute sulphuric acid / hydrochloric acid to the sample 1Copper(II) oxide dissolves / a blue solution is formed 1Filter off the copper powder 1Wash the copper powder with water and allow it to dry 1Weigh the copper powder 1
Percentage by mass of copper powder in the sample =
1E.C. = 3
17 . 00/I/7.(a)
The sour taste of citrus fruit is mainly due to citric acid which is a weak acid with the following structure :
(i) What is the meaning of the term ‘weak acid’ ?(ii) Given that citric acid is a tribasic acid, write a chemical equation for the complete neutralization of citric acid by sodium hydroxide solution.(iii) In a titration experiment to determine the concentration of citric acid in orange juice, 25.0 cm3 of a sample of orange juice required 10.0 cm3 of 0.3 M sodium hydroxide solution to reach the end-point, at which the citric acid had been completely neutralized.
(1) Given that the relative molecular mass of citric acid is 192, calculate the concentration of citric acid, in g dm-3, in sample of orange juice.(2) State ONE assumption in your calculation in (1).(3) Given the following materials and apparatus, briefly describe how a 0.30 M sodium hydroxide solution can be prepared.
1.20 M sodium hydroxide solution, distilled water, 25.0 cm3 pipette, 50.0 cm3 volumetric flask, 100.0 cm3 volumetric flask, and 250 cm3 volumetric flask (Only one of these flasks should be used.)
(10 marks)
SOLUTION :
(i) An acid which undergoes incomplete ionization in water. 1
(ii)
1
(iii) (1) no. of moles of NaOH used = 0.30 10 10-3 1 molarity of citric acid in orange juice
=
1 = 0.04 moldm-3
1 concentration of citric acid in orange juice
HO C CO2H
CH2CO2H
CH2CO2H
HO C CO2H
CH2CO2H
CH2CO2H
+ 3 OH- HO C CO2-
CH2CO2-
CH2CO2-
+ 3 H2O
= 0.04 192 = 7.68 gdm-3 1(2) citric acid is the only substance in orange juice which reacts with NaOH 1
(3) Use the pipette to transfer 25.0 cm3 of the 1.20 M NaOH to the 100 cm3 volumetric flask 2 Add water to the volumetric flask until the graduation mark is reached. 1
18 . 00/I/8.(c)
State whether each of the following statements is true or false. Explain your answer in each case.When concentrated sulphuric acid is diluted, water should be added slowly to the acid.
(2 marks)
SOLUTION :
False, dilution of concentrated H2SO4 is a highly exothermic process. The heat evolved may cause the acid to splash out. 2
19 . 99/I/7.(b)
A student carried out the following experiment to determine the concentration of ethanoic acid in a brand of commercial vinegar.
‘25.0 cm3 of the vinegar was placed in apparatus Y and was then diluted to 250.0 cm3 with distilled water. 25.0 cm3 of the diluted vinegar solution was withdrawn and titrated against 0.10 M sodium hydroxide solution with phenolphthalein as indicator.’
(i) (1) Name apparatus Y. (2) Suggest ONE reason for diluting the vinegar.(ii) State the colour change at the end point of the titration.
(iii) The student carried out four titration altogether. The titration results are listed in the table below :
TitrationBurette reading
1 2 3 4
Final reading / cm3 23.90 23.60 23.10 23.60
Initial reading / cm3 3.00 3.50 3.10 3.40
(1) Based on the titration results, calculate a reasonable average for the volume of the sodium
hydroxide solution used. (2) Calculate the concentration, in mol dm-3, of ethanoic acid in the vinegar.
(iv) Explain why vinegar can be used as a food preservative.(9 marks)
SOLUTION :
(i) (1) Volumetric flask. 1
(2) To save chemicals. 1 / the concentration of the titrant should be comparable to that of the titrate.
(ii) (1) Titration 1 : volume used = 23.90 – 3.00 = 20.90 cm3
Titration 2 : volume used = 23.60 – 3.50 = 20.10 cm3
Titration 3 : volume used = 23.10 – 3.10 = 20.00 cm3
Titration 4 : volume used = 23.60 – 3.40 = 20.20 cm3
The result of titration 1 is inaccurate and is discarded. 1 The reasonable average for the volume used = (20.10 + 20.00 + 20.20) / 3 = 20.10 cm3 1
(2) CH3CO2H + NaOH CH3CO2Na + H2O 1
concentration of CH3CO2H in vinegar
=
= 0.804 mol dm-3 1
(iv) The low pH of vinegar can prevent the growth of bacteria. 1
20 . 98/I/6.(a)
A student prepared sodium nitrate solution by reacting 1 M sodium hydroxide solution with dilute nitric acid. The student carried out a titration to determine the amount of dilute nitric acid required to react with a known volume of 1 M sodium hydroxide solution.
(1) Write the chemical equation for the reaction. (An ionic equation will NOT be accepted for this question.)
(2) Draw a labelled diagram for the set-up of the titration.
(3) Phenolphthalein can be used to determine the end point of the titration. State the colour change at the end point.
(4) Suggest how the student can prepare a sodium nitrate solution using the titration results.
(6 marks)
SOLUTION :
(1) NaOH + HNO3 NaNO3 + H2O 1
(2)
3
Sodium hydroxide + phenolphthalein
Conical flask
Nitric acid
Burette
(3) From pink to colourless. 1
(4) Add dilute nitric acid to 1 M sodium hydroxide solution in the same volume ratio as that in the titration result, without adding the indicator. 1
21 . 98/I/8.(a)
A student added concentrated sulphuric acid dropwise to some sugar cubes as illustrated in the diagram below :
(i) (1) State the observable changes in the above experiment and write the chemical equation for the reaction involved.
(2) What proerty of concentrated sulphuric acid is responsible for the reaction ?
(ii) When there was no further change, the student added excess concentrated sulphuric acid to the reaction mixture. Upon heating, carbon dioxide, sulphur dioxide and water were produced.
(1) Write the chemical equation for the reaction that occurred during heating.
(2) What property of concentrated sulphuric acid is responsible for this reaction ?
(3) State ONE safety precaution that should be taken. Explain your answer.
(iii) Draw ONE hazard warning label which should be displayed on a bottle of concentrated sulphuric acid.
(9 marks)
SOLUTION :
concentrated sulphuric acid
sugar cubes
(i) (1) sugar chars 1 misty fumes evolved 1
C12H22O11 12C + 11H2O 1
(2) dehydrating 1
(ii) (1) C + 2H2SO4 CO2 + 2SO2 + 2H2O 1
(2) Oxidizing 1
(3) The experiment should be carried out in a fume cupboard 1 because the experiment produces SO2 which is toxic 1
(iii)
1
22 . 97/I/3
(a) Suggest ONE method to determine the pH of an aqueous solution.
(b) Arrange the following substances in the order of increasing pH and explain your answer.
1M ethanoic acid, 1M hydrochloric acid, 1M sulphuric acid
(c) Three solution samples, A, B and C, are being tested for the purpose of perming hair. The table below lists the pH of these samples :
Sample pH
A 6.5
B 8.5
C 10.0
Which sample is most suitable for perming hair ? Explain your answer.
(6 marks)
SOLUTION :
(a) 1
(b)
3(c)
2
23 . 97/I/7.(a)
Malachite is a mineral containing copper(II) carbonate and copper(II) hydroxide. It is insoluble in water but reacts with dilute sulphuric acid. The procedure for preparing copper(II) sulphate crystals from malachite is as follows :
Step 1 Pour 50 cm3 of 2M sulphuric acid in a beaker and then warm the acid.
Step 2 Add small portions of powdered malachite to the warm acid while constantly stirring, until effervescence stops and some powdered malachite remains in the beaker.
Step 3 Remove the remaining powdered malachite from the solution.
Step 4 Evaporate the solution slowly to obtain copper(II) sulphate crystals.
(i) Write a chemical equation for the reaction which causes the effervescence.
(ii) Why is it necessary to add powdered malachite until some of it remains in the beaker ?
(iii) Draw a labelled diagram to show how the remaining powdered malachite can be removed from the solution.
(iv) Calculate the theoretical mass of copper(II) sulphate crystals, CuSO4.5H2O, that can be obtained.
(Relative atomic masses : H = 1.0, C = 12.0, O = 16.0, S = 32.1, Cu = 63.5)
(8 marks)
SOLUTION :
(i) 1
(ii) 1
(iii)
3
(iv)
3
24 . 96/I/6.(b)
A, B, C and D are four unlabelled bottles, each containing one of the following reagents :
2M ammonia solution, 2M ethanoic acid,2M hydrochloric acid, 2M nitric acid.
The following scheme is used to identify the four reagents :
Reagent in bottle A, B, C or D.
Add a piece of red litmus paper.
(i) What is the reagent in bottle A ? Explain why this reagent turns red litmus paper blue.
(ii) What is the reagent in bottle B ? Write a chemical equation for the reaction between this reagent and copper turnings, and a chemical equation for the formation of the brown fumes.
(iii) (1) Suggest a test to distinguish between the reagents in bottles C and D.
(Smelling the reagents is NOT an acceptable answer.)
(2) State the observable change in this test and explain your answer.
(8 marks)
SOLUTION :
(i) A is 2M ammonia 1 Ammonia ionizes in water to give OH- which turns red litmus paper blue / ammonia solution is alkaline. 1
(ii) B is 2M nitric acid 1
3Cu + 8HNO3 3Cu(NO3)2 + 2NO + 4H2O 1
Does the red litmus paper turn blue ? Reagent in bottle A
Yes
No
Add copper turnings and warm the mixture.
Reagent in bottle B
Reagent in bottle C or D
Yes
No
Are brown fumes evolved ?
2NO + O2 2NO2 1
(iii) (1) Add a piece of pH paper / add a few drops of indicator 1
(2) HCl will give a lower pH / a deeper colour because HCl ionizes to a greater extent than CH3COOH 2
25 . 95/Sample Paper/8.(a)
The table lists some information about two brands of anti-acids tablets P and Q , both containing magnesium hydroxide, Mg(OH)2 as the active ingredient :
Brand Price per tablet Mass per tablet Mass of Mg(OH)2 per tablet
P $0.75 1.30 g unknownQ $0.60 1.10 g 0.80 g
A student carried out the following experiment to determine the mass of magnesium hydroxide per tablet of anti-acid, P :
A tablet of anti-acid P was ground to a powder which was then added to a conical flask containing some distilled water and a few drops of methyl orange. The content of the flask was titrated against standard hydrochloric acid. It was found that 25.2 cm3 of 1.50M hydrochloric acid were required for complete reaction.
(i) Explain the meaning of the term ‘standard hydrochloric acid’.
(ii) Why was methyl orange added to the conical flask ? What would be observed at the end-
point of the titration ?
(iii) Write the chemical equation for this reaction. (Ionic equation will NOT be accepted.)
(iv) Calculate the mass of magnesium hydroxide per tablet of P.
(v) Shown by calculation, which of the two brands of anti-acid tablets has a lower price per gram of magnesium hydroxide.
(Relative atomic masses : H = 1.0, O = 16.0, Mg = 24.3)(10 marks)
SOLUTION :
(i). It means that the solution has a known concentration. 1
(ii). Methyl orange is added as an indicator. 1 The solution turns red from yellow at the end point. 1
(iii).
1
(iv).
m = 1.102 g3
(v).
P = 1.47
Q = 1.33
26 . 95/I/6.(a)
The illustration below shows the plastic bottle of a domestic toilet cleaner and its label.
(i) Explain, with the help of a chemical equation, why the toilet cleaner should not be mixed with bleaches.
(ii) (1) Suggest ONE chemical, other than bleaches, that should not be mixed with the toilet cleaner.
(2) If the chemical suggested in (1) and the toilet cleaner are mixed together, what change would be observed ? Write a chemical equation for the reaction involved.
LIQUID TOILET CLEANER
New formulation contains HCl
Caution :(1) Do not mix with bleaches or other chemicals.(2) Handle with care.
(iii) Explain why it is necessary to handle the toilet cleaner with care.
(iv) (1) Explain why plastic is used for making the bottle for the toilet cleaner.
(2) Name ONE plastic material suitable for making the bottle for the toilet cleaner.
(9 marks)
SOLUTION :
(i) The H+ ions in the toilet cleaner will react with the bleach 1 (ClO- and Cl-) to give chlorine which is toxic. 1
Cl- + ClO- + 2H+ Cl2 + H2O 1
(ii) (1) Chemical : 1
(2) Change : 1
Equation : 1
(iii) 1
(iv) (1) It is inert. 1
(2) 1
27 . 95/I/7.(a)
The label of a bottle of ‘Effervescent Calcium’ tablets is shown below.
(i) Effervescence occurs when a tablet of ‘Effervescence Calcium’ added to water. Based on the information given on the tablet, explain why effervescence occurs. Write ionic equation for the reaction that occurs.
(ii) Suppose that a student puts a tablet of ‘Effervescence Calcium’ into an excess amount of water and collects the gas liberated.
(1) Assuming that the tablet completely dissolves, calculate the theoretical volume of gas liberated.
(2) It is found that the volume of gas collected in the experiment is less than the theoretical volume calculated in (1). Give ONE reason to explain the difference, assuming that there is no leakage of gas in the experiment.
Effervescent Calcium
Each bottle contains 10 tablets.
Each tablet contains :Calcium carbonate 625 mgVitamin C 1000 mgCitric acid 1350 mg
Dosage : 1 tablet daily
Administration : Dissolve one tablet in a glass of water.
Warning : (1) Keep out of reach of children. (2) Keep ......................................
(iii) On the label, some words are missing in the second warning statement. Complete the second warning statement, beginning with the word ‘Keep’. Explain your answer.
(Relative atomic masses : C = 12.0, O = 16.0, Ca = 40.0 ; Molar volume of gas at room temperature and pressure = 24.0 dm3)
(9 marks)
SOLUTION :
(i) Citric acid / vitamin C when dissolves in water give H + (aq) which reacts with calcium carbonate to give gas bubbles. 2
CaCO3 + 2H+ Ca2+ + CO2 + H2O 1
(ii) (1)
3 (2) 1
(iii) Keep out of moisture 1
Reason : The active ingredients of the tablet will react in the presence of water. 1
28 . 94/I/5.(a)
A domestic drain cleaner named “RAINBOW’ contains concentrated sulphuric acid as the active ingredient. A student carried out the following experiment to determine the concentration of sulphuric acid in ‘RAINBOW’.
1.0cm3 of ‘RAINBOW’ was diluted to 500cm3 with distilled water . 25.0cm3 of the diluted solution were measured and transferred to a conical flask. The solution in the flask required 18.2cm3 of 0.1M sodium hydroxide solution for complete neutralization.
(i) Name the apparatus used to measure 25.0cm3 of the diluted solution.
(ii) Calculate the molarity of sulphuric acid in ‘RAINBOW’.
(iii) Suggest ONE disadvantage of using ‘RAINBOW’ for cleaning drains.
(iv) State ONE safety precaution needed when using ‘RAINBOW’. Explain your answer.(v) If ‘RAINBOW’ is poured into drains blocked with fat, the fat can be removed. Assuming the formula of fat is
(R represents an alkyl group),
explain how ‘RAINBOW’ can remove fat.
(8 marks)
SOLUTION :
(i) 1
(ii)
2
(iii) It may cause corrosion to the iron drainage pipes. 1
(iv) 2
H
H
H
H
O
O
O
O
O
O
H
CC
CC
CC
R
R
R
(v) Pouring ‘RAINBOW’ to the drain causes hydrolysis of the fat into more soluble products which can easily be removed by draining of water. 2
29 . 93/I/1.(b) Liquid wastes discharged from some factories are acidic and need to be neutralized before discharging into the sea. A certain factory used slaked lime (calcium hydroxide) to neutralized its liquid waste, which consisted of 0.5M hydrochloric acid, discharging at a rate of 20dm3 per minute.
(i) Why are the liquid wastes neutralized before discharging into the sea ?
(ii) Write an equation for the reaction between hydrochloric acid and slaked lime.
(iii) Calculate the mass of slaked lime required per minute to neutralize the acid present in the liquid wastes.
(iv) Although slaked lime is cheaper, factories nowadays use sodium carbonate instead of slaked lime to neutralize their acidic liquid wastes. Suggest a reason.
(Relative atomic masses : H = 1.0; O = 16.0; Ca = 40.0)
(6 marks)
SOLUTION :
(i). Harmful to aquatic species. 1
(ii). Ca(OH)2 + 2HCl CaCl2 + 2H2O 1
(iii).
3
(iv). Calcium ions forms a number of insoluble salt. 1
30 . 92/I/1.(a)
A student tries to prepare a sample of a solid salt by reacting copper(II) oxide with sulphuric acid in the laboratory as shown in the diagram below.
The student wrote the following procedure of the experiment in her notebook :
I. Excess copper(II) oxide was added to 50.0cm3 of 2.0M sulphuric acid in a beaker.
II. The mixture was heated for 2 minutes, and was stirred continuously during this time.
III. The remaining copper(II) oxide was filtered off.
IV. The filtrate was allowed to cool for one day.
(i). Referring to the above diagram, write down TWO aspects that are considered UNSAFE in the laboratory.
(ii). (1) Name the salt the student tried to prepare.
(2) Calculate the theoretical mass of the salt that can be obtained.
(iii). Explain why the student heated the reaction mixture in step II.
(iv). The student followed exactly the procedure written in her notebook, but did not obtain any SOLID salt after one day. Suggest an explanation.
(Relative atomic masses : H = 1.0; O = 16; S = 32; Cu = 63.5)
(8 marks)
SOLUTION :
(i) Hair not tied up / bottle not stoppered. 2
(ii) (1) 1
(2)
2
(iii) To speed up reaction. 1
(iv) The filtrate is not concentrated enough. 1
31 . 91/I/2.(a)
A student wished to find out which if the two commercial brands of vinegar, A and B, was better buy, i.e. of lower price per gram of ethanoic acid (CH3COOH). The following table listed some of the information about these two brands :
Brand Price Volume of vinegar Concentration of ethanoic acidA $3.00 250cm3 50 g dm3
B $6.00 500cm3 UNKNOWN
The student carried out a titration experiment to determine the concentration of ethanoic acid in Brand B as follows :
25.0 cm3 of the vinegar was first distilled to 250 cm3 with distilled water. 25.0 cm3 portions of the diluted solution were then titrated against 0.10M sodium hydroxide solution with methyl orange, until the end-point was reached.
The following results were obtained :
Titration 1 2 3 4Burette reading
Final reading (cm3) 25.50 25.70 26.20 25.90
Initial reading (cm3) 0.00 1.00 1.30 1.20
(i) Describe, giving the names of the apparatus used, how 25.0cm3 of the vinegar should be
diluted to 250.0 cm3.
(ii) Why is methyl orange added into the solution mixture and state what could be observed at the end-point.
(iii) Based on the titration results, calculate a reasonable average for the volume of the sodium hydroxide solution used.
(iv) Write the equation for this titration. (Ionic equation will not be accepted.)
(v) Calculate the molarity of ethanoic acid in Brand B.
(vi) Shown by calculation which brand of vinegar is the better buy.
(Relative atomic masses : H = 1.0; C = 12.0; O = 16.0)
(13 marks)
SOLUTION :
(i)
3
(ii) As an indicator, it turns to pink from colourless. 2
1
(iii)
(iv) CH3COOH + NaOH CH3COONa + H2O 1
(v)
3
(vi)
3
32 . 89/I/2.(a)
Antiacid tablets are used to relieve pains caused by excess acid in the stomach.The label (in English and Chinese) on a brand of antiacid, called “Consonant”, is shown in the diagram below :
The following experiment was performed by a student to find out the amount of calcium carbonate in such a tablet :
Steps :
(1) A tablet was weighted and ground to a powder, and then added to a conical flask containing some distilled water.
(2) A few drops of methyl orange indicator were added to the flask. Standard hydrochloric acid was then added from burette in small portions, with swirling.
(3) On adding each portion of the acid, the solution in the flask first turned pink and then yellow upon swirling. Effervescence was also observed.
(4) More acid was added until a permanent pink colour was just observed.
Experiment Results :
Mass of one tablet = 1.20 g
Volume of the hydrochloric acid used = 15.2 cm3
Concentration of the hydrochloric acid = 1.00 M
(i) Explain the meaning of the term “Standard” in step (2).
(ii) In step (3), explain
(1) the colour changes in the solution.(2) why effervescence was observed.
(iii) In step (4), explain why a permanent pink colour was observed.
(iv) Calculate the percentage by mass of calcium carbonate in one antiacid tablet.
(Relative atomic masses : C = 12.0; O = 16.0; Ca= 40.0)
(v) On the label, it was recommended that the tablets should be chewed before swallowing. Suggest an explanation for this.
(vi) Antiacid tablets containing calcium carbonate are seldom used nowadays. Instead, magnesium hydroxide is usually used as the active ingredient. Based on the reactions
involved, suggest one reason why magnesium hydroxide is preferred to calcium carbonate.
(13 marks)
SOLUTION :
(i) “Standard” means that the concentration is known. 1
(ii) (1) The solution first turn pink, because as the acid is dropped into the flask, at first region near the point of contact is still acidic. pink colour. Upon swirling, the resulting solution after reaction is not acidic, hence the yellow colour is restored.
2 (2) The effervescence is due to the liberation of CO2. 1
(iii) When all CaCO3 has reacted, a slight excess of acid would make the solution acidic, thus the solution would turn pink, showing the acid colour of the indicator. 1
(iv)
4 (v) Chewing breaks down the tablet into smaller pieces, this would give more surface area for reaction with the acid, and faster relief. 2
(vi) No carbon dioxide produced in this process, thus there will be no pressure built up in the stomach. 2
33 . 88/I/2.(a)
14.80 g of a dibasic acid (H2X) were dissolved in distilled water and made up to 100.0 cm3. The acid
solution was then added, 5.0 cm3 at a time, to 50.0 cm3 of 2.0 M sodium hydroxide solution in a polystyrene cup. The resultant solution was stirred and the temperature after each addition of the acid
solution was recorded until a total volume of 75.0 cm3 of acid had been added. The results obtained are represented by the graph shown below :
temp./C
20 30100 60 80705040
20
15
30
25
40
35
45
volume of H2X solution added/cm3
the acid solution was recorded until a total volume of 75.0cm3 of acid had been added. The results obtained are represented by the graph shown below :
(i) Explain why a polystyrene cup was used in this experiment.
(ii) (1) What is meant by the term 'dibasic acid” ? (2) Write an equation for the complete neutralization of H2X by sodium hydroxide solution. (An ionic equation will NOT be accepted.)
(iii) Explain the rise and fall in temperature shown in the graph.
(iv) What was the maximum temperature reached in this experiment ?
(v) What volume of acid solution was required to neutralize the sodium hydroxide solution in the polystyrene cup ?
(vi) Calculate the concentration (in mol dm-3) of the H2X solution and hence deduce the relative molecular mass of H2X.
(12 marks)
SOLUTION :
(i) It is a good heat insulator. 1
(ii) (1) An acid which can produce two hydrogen ions per molecule of the acid when dissolved in water. 1
(iii) Before reaching the end point, adding acid solution to the alkali caused liberation of heat. The more acid added, the more heat liberated, hence the temperature increased. 1
After reaching the end point, all alkali had been reacted. The addition of acid solution at room temperature caused a decrease in temperature for the solution. 2
(iv) 36.0C 1
(v) 43.0 cm3 1
(vi)
4
34 . 88/I/4.(b)
Four reagent bottles, labelled as A, B, C and D contained four different solutions. These solutions were known to be :
dilute sodium hydroxidedilute sodium chloridedilute sulphuric acidconcentrated nitric acid
The following tests were carried out to identify the solution :
Test Procedure ObservationI Copper turnings were added to each
solution contained in separate test-tubes.
A blue solution was obtained and brown fumes were evolved with the solution from bottle A. No apparent change was observed for other solutions.
II The blue solution from Test I was added to three test-tubes containing solutions from bottles B, C, and D.
A bluish-white precipitate was obtained with the solution from bottle B. No precipitate was observed for the other solutions.
III The precipitate obtained in Test II was divided into two parts, and added separately to two test-tubes containing solutions from bottles C and D.
The precipitate dissolved in the solution from bottle C, but not in the other solution.
Based on the information, (i) identify the solution. (ii) briefly explain the observation.
(8 marks)
SOLUTION :
(i) A : 1
B : 1
C : 1
D : 1
(ii) Test I : copper was oxidized to form a blue solution of copper(II) nitrate. 1 the nitric acid was reduced to form brown fumes of nitrogen dioxide. 1
or
Test II : copper ions are precipitate by the alkali to form a blue ppt. of copper(II) hydroxide. 1
or
Test III : the precipitate is a base and reacts with an acid to form a blue solution. 1
or
35 . 86/I/1.(b)
Acidic substances, such as sodium hydrogensulphate are present in some toilet cleaning powders.
(i) How would you show the presence of acidic substances in a toilet cleaning powder ?
(ii) Briefly describe the preparation of large crystals of sodium hydrogensulphate from 2M sulphuric acid and 2M sodium hydroxide.
(6 marks)
SOLUTION :
(i) Dissolve the cleaning powder in water, and test for acidity by using a piece of pH paper. The pH paper would turn red. 2
(ii) Mix together equal volumes of 2M sulphuric acid and 2M sodium hydroxide, concentrate the solution by evaporation, cool slowly and then filter. 4
36 . 86/I/2.(b)(i)
Sodium hydrogencarbonate decomposes upon heating to give carbon dioxide. What volume of carbon dioxide at room temperature and atmospheric pressure can be obtained by decomposing 1.00 g of sodium hydrogencarbonate ?
(Relative atomic masses : H = 1.00, C = 12.0, O = 16.0, Na = 23.0)(Molar volume at room temperature and atmospheric pressure = 24.0 dm3)
(4 marks)
SOLUTION :
4
37 . 86/I/5.(c)
0.27 g of magnesium ribbon was dropped into a conical flask containing 25.0 cm3 of 0.500 M sulphuric acid. After reaction, the excess acid was titrated against 0.203 M sodium hydroxide solution, and 21.50 cm3 of the base were required for neutralization.
(Relative atomic mass of magnesium = 24.3)
(i) Write an equation for the reaction between magnesium and sulphuric acid.
(ii) From the titration data, calculate
(1) the number of moles of sodium hydroxide used to neutralize the excess acid.
(2) the number of moles of sulphuric acid which have reacted with magnesium.
(3) the percentage purity of the magnesium ribbon.
(iii) According to the manufacturer, the purity of the magnesium ribbon was 99.6%, but the purity determined in (ii) (3) was lower than this value.
(1) Suggest a possible reason for this difference.
(2) Suggest how the experimental procedure could be improved to obtain a purity determination closer to 99.6%.
(8 marks)
SOLUTION :
(i) 1
(ii) (1) no. of moles of NaOH used to neutralize the acid,
= 2150
10000 203
..
= 0.00436 1
(2) no. of moles of H+ reacted with Mg,
= 050 250
10002 0 00436
. .( . )
= 0.0206 1
no. of moles of H2SO4 used,
= 0.0206 2
= 0.0103 1
(3) mass of Mg reacted with acid,
= 24.3 0.0103
= 0.250 g 1
Percentage purity of magnesium,
= 0 25
0 27100%
.
.
= 92.7% 1
(iv) (1) The magnesium ribbon may be coated with an oxide layer due to exposure to air. 1
(2) Clean the surface of the magnesium ribbon before weighing. 1
38 . 83/I/4.(a)
A student put 25 cm3 of 0.1 M sulphuric acid solution into a flask. The student then added 5 cm3 of a sodium hydroxide solution, swirled the solution thoroughly and estimated the pH value of the resulting solution by means of pH paper. The process was repeated until 50 cm3 of sodium hydroxide solution had been added. The following graph gives the approximate pH values and the volume of sodium hydroxide solution added :
(i) Write an ionic equation for the reaction between sulphuric acid and sodium hydroxide solution.
(ii) By identifying the point on the graph where all the sulphuric acid had completely reacted with the sodium hydroxide solution, determine, at this point,
(I) the pH value of the solution, and
(II) the volume of sodium hydroxide solution added.
(iii) Calculate the concentration (in mol dm-3) of the sodium hydroxide solution used in this
experiment.
(iv) The sulphuric acid used in this experiment is referred to as a ‘strong acid’. What is meant by this term ?
(7 marks)
SOLUTION :
(i) 1
(ii) (I) 1
(II) 1
(iii)
3
(iv) A strong acid is an acid which is completely ionized in solution. 1
SOLUTIONS TO SECTION 4
EXAMPLE IV-XII
Na2CO3.nH2O(s) Na2CO3(aq) + nH2O(l)
Na2CO3 + H2SO4 Na2SO4(aq) + CO2(g) + H2O(l)
No. of moles of H2SO4 = 0.05 28/1000 = 1.4 10-3
No. of moles of Na2CO3 in 25 cm3 = 1.4 10-3
No. of moles of Na2CO3 in 250 cm3 = 1.4 10-3 10 = 1.4 10-2
n = 10
22 . 97/I/3
(a) pH meter
(b) Increasing pH : H2SO4 HCl CH3COOH
CH3COOH has highest pH as it is a weak acid which slightly ionize in waterH2SO4 has lowest pH as it is a dibasic acid which gives 2 moles of H+ when 1 mole of acid dissolves in water
(c) B A is not used as it is not alkaline. While C is not used as it is too strong that would damage our hair.
23. 97/I/7.(a)
(i) CuCO3 + H2SO4 CuSO4 + CO2 + H2O
(ii) To ensure the malachite is in excess
(iii)
(iv) no. of moles of H2SO4 = 2 50/1000 = 0.1 no. of moles of CuSO4 = 0.1
m = 0.1 [63.5 + 32.1 + 16(4)] = 24.96 g
25. 95
(iii) Mg(OH)2 + 2HCl MgCl2 + 2H2O
(iv) no. of moles of HCl = 1.5 25.2/1000 = 0.0378 no. of moles of Mg(OH)2 = 0.0378 0.5 = 0.0189 m = 0.0189 [24.3 + (16 + 1)2] = 1.1g
(v) P : 0.75/1.1 = 0.68 Q : 0.6/0.8 = 0.75
P is cheaper
26. 95/I/6.(a)
Filter funnel
Filter paper
residue
filtrate
(ii) (1) Chemical : Metal such as Mg
(2) Change : Colourless gas bubbles observed
(3) Equation : Mg + 2HCl MgCl2 + H2
(iii) As it is corrosive
(iv) (2) polyethene
27. 95/I/7.(a)
(ii) (1) CaCO3 + 2H+ Ca2+ + CO2 + H2O
no. of moles of CaCO3 =
= 6.25 10-3
no. of moles of CO2 = 6.25 10-3
Vol. = 6.25 10-3 24 = 0.15 dm3
(2) CO2 will dissolve in the solution
28. 94/I/5.(a)
(i) Pipette
(ii) No. of moles of NaOH = 0.1 18.2/1000 = 1.82 10-3
H2SO4 + 2NaOH Na2SO4 + 2H2O
No. of moles of H2SO4 in 25 cm3 = 1.82 10-3 0.5 = 9.1 10-4
No. of moles of H2SO4 in 500 cm3 = 9.1 10-4 20 = 0.082 Molarity = 0.0182 1000 = 18.2 M(iv) Wear safety gloves as it is highly corrosive
29. 93/I/1.(b)
(iii) no. of moles of HCl = 0.5 20 = 10 no. of moles of Ca(OH)2 = 10 0.5 = 5 m = 0.5 [40 + (16 + 1)]
= 37 g
30. 92/I/1.(a)
(ii) (1) hydrated copper(II) sulphate
(2) no. of moles of H2SO4 used = 2 50/1000 = 0.1 CuO + H2SO4 CuSO4 + H2O No. of moles of salt formed = 0.1 m = 0.1 (63.5 + 32+ 16 4 + 5 18) = 24.95g
31. 91/I/2.(a)
(i) Use a pipette to transfer 25.0 cm3 of the solution into a 250 cm3 of volumetric flask Then add distilled water to the graduation mark
(iii) Average =
= 24.80 cm3
(v) no. of moles of CH3CO2H in 25 cm3 of diluted vinegar no. of moles of NaOH used = 0.1 24.8/1000 = 2.48 10-3
no. of moles of CH3CO2H in 250 cm3 of diluted vinegar = 2.48 10-3 250/25 = 2.48 10-2
conc. of the original solution = 2.48 10-2 1000/25 = 0.992 M
Brand A : The mass of CH3CO2H in a bottle = 50 250/1000 = 12.5 g
Price per g of CH3CO2H = 3.0/12.5 = $0.24
Brand B : The mass of CH3CO2H in a bottle = 0.992 60 500/1000 = 29.76 g
Price per g of CH3CO2H = 6.0/29.76 = $0.2
B is better buy
32. 89/I/2.(a)
CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
No. of moles of CaCO3 in one tablet= 15.2/1000 0.5mass of CaCO3 = 15.2/1000 0.5 100 = 0.76 g% by mass = 0.76/1.2 100 = 63.3 %
33. 88/I/2.(a)
(vi) no. of moles of NaOH used = 50/1000 2 = 0.1
no. of moles of H2X required = 0.1 0.5 = 0.05
conc. of H2X solution = 0.05 1000/43 = 1.16 M relative molecular mass of H2X
=
= 128
34. 88/I/4.(b)
(i) A : conc. nitric acid B : sodium hydroxide C : dil. sulphuric acid D : sodium chloride
35. 86/I/2.(b)
2NaHCO3 Na2CO3 + CO2 + H2O
no. of moles of NaHCO3 = 1.00/84.5 = 0.012no. of moles of CO2 evolved = 0.012 0.5 = 5.9 10-3
Vol. = 5.9 10-3 24 = 0.142 dm3
38. 83/I/4.(a)
(i) H+(aq) + OH-(aq) H2O(l)
(ii) From the graph (I) pH = 7 (II) volume of sodium hydroxide added = 28 cm3
(iii) no. of moles of H2SO4 in 25 cm3
= 0.1 25/1000 = 0.0025
no. of moles of NaOH in 28 cm3
= 0.0025 2 = 0.005
conc. of NaOH= 0.005 /28 10-3 = 0.1786 M
EXERCISE B :
1. Which of the following substances is used by farmers to increase the pH of soil ?
A. ammonium nitrateB. calcium hydroxideC. citric acidD. potassium hydroxide
2. Which of the following experiments can be used to show that concentrated sulphuric acid is a dehydrating agent ?
A. adding it to copper(II) oxide powderB. adding it to copper(II) sulphate crystalsC. adding it to calcium carbonate powderD. adding it to sodium chloride crystals
3. A student added 16 cm3 of 2M sodium hydroxide solution, in 2 cm3 portions, to 10 cm3 of 2M nitric acid. He measured the temperature of the mixture immediately after each addition of the sodium hydroxide solution.
Which of the following graphs represents the relationship between the temperature of the mixture and the volume of sodium hydroxide solution added ?
A.
temp.
volume of NaOH(aq) added0
B.
temp.
volume of NaOH(aq) added0
C.
temp.
volume of NaOH(aq) added0
D.
temp.
volume of NaOH(aq) added0
4. In an experiment, 1.6 g of sulphur are burnt completely in air to form sulphur dioxide. What volume of sulphur dioxide, measured at room temperature and pressure, is formed ?
(Relative atomic mass : S = 32.0 ; Molar volume of gas at room temperature and pressure = 24.0 dm3)
A. 0.6 dm3
B. 1.2 dm3
C. 2.4 dm3
D. 12.0 dm3
5. One mole of each of the following compounds is burnt completely in oxygen. Which compound requires the greatest volume of oxygen, measured at the same temperature and pressure, for complete combustion ?
A. carbon monoxideB. ethaneC. etheneD. ethanol
6. Which of the following substances, when mixed, will undergo a reaction ?
A. vinegar and anti-acidB. bleach and anti-acidC. vinegar and table saltD. bleach and table salt
7. Under certain conditions, 60 cm3 of a gaseous compound. NxOy, decompose completely give 60 cm3 of nitrogen gas and 30 cm3 of oxygen gas. (All gas volumes are measured at the same temperature and pressure.)
Which of the following combinations is correct ?
x yA. 1 1 B. 1 2C. 2 1D. 2 3
8. Which of the following statements concerning one mole of nitrogen gas is/are correct ?
(1) It has a mass of 14.0 g.(2) It occupies the same volume as 4.0 g of helium gas at room temperature and pressure.(3) It contains 6.02 1023 atoms of nitrogen.
(Relative atomic masses : He = 4.0, N = 14.0, Avogardo constant = 6 1023 mol-1)
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
9. In order to prepare 250 cm3 of 0.10 M sodium hydroxide solution from 1.0 M sodium hydroxide solution, which of the following combinations of apparatus should be used ?
A. burette, measuring cylinder, pipetteB. conical flask, measuring cylinder, volumetric flaskC. burette, conical flask, wash bottleD. pipette, volumetric flask, wash bottle
10. A student performed a titration experiment in which he added an acid from a burette to an alkali contained in a flask. The following diagrams show the initial and final readings of the burette.
What was the volume of the acid added from the burette to the conical flask ?
A. 24.5 cm3
B. 24.6 cm3
C. 24.7 cm3
D. 32.3 cm3
11. Which of the following pairs of solutions, when mixed, would give a neutral solution ?
A. 10 cm3 of 1 M sulphuric acid and 10 cm3 of 1 M sodium hydroxide solutionB. 10 cm3 of 1 M sulphuric acid and 10 cm3 of 2 M sodium hydroxide solutionC. 10 cm3 of 2 M sulphuric acid and 20 cm3 of 1 M sodium hydroxide solutionD. 20 cm3 of 2 M sulphuric acid and 10 cm3 of 2 M sodium hydroxide solution
12. The reaction of cane sugar and concentrated sulphuric acid may be represented by the following equation.
C12H22O11(s) conc H SO. 2 4 12C(s) + 11H2O(l)
In this reaction, concentrated sulphuric acid acts as A. a strong acid
B. an oxidizing agentC. a drying agentD. a dehydrating agent
13. What volume of water is required to dilute 100 cm3 of 8M hydrochloric acid to a concentration of 2M ?
A. 200 cm3
B. 300 cm3
C. 400 cm3
D. 700 cm3
14. Referring to the following equation :
Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)
What volume of carbon dioxide, measured at room temperature and pressure, is produced if 244 g of iron are formed ?
(Relative atomic mass : Fe = 56; Molar volume of gas at room temperature and pressure = 24 dm3)
A. 16 dm3
B. 36 dm3
C. 72 dm3
D. 144 dm3
15. Which of the following substances, when mixed with lemon juice, would give off gas bubbles ?
(1) iron nails(2) milk of magnesia(3) polystyrene wrap
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
16. Which of the following contains the same number of atoms as 2.20 g of carbon dioxide ?
(Relative atomic masses : H = 1.0, C = 12.0, N = 14.0, O = 16.0, S = 32.0, Cl = 35.5)
A. 1.70 g of ammoniaB. 2.25 g of nitrogen monoxideC. 2.80 g of sulphur dioxideD. 3.55 g of chlorine
17. A metal X forms a hydroxide XOH. 1.12 g of XOH were dissolved in some distilled water and then made up to 250 cm3 with distilled water. 25.0 cm3 of this solution required 20.0 cm3 of 0.10 M hydrochloric acid for complete neutralization. What is the relative atomic mass of X ?
(Relative atomic masses : H = 1.0, O = 16.0)
A. 23.0B. 24.0C. 39.0D. 40.0
18. Which of the following statements concerning a solution of hydrogen chloride in dry methylbenzene is correct ?
A. It can conduct electricityB. Its pH value is smaller than 7C. When magnesium is added to it, a gas is evolved.D. When ammonia gas is bubbled into it, a white precipitate is formed
19. The formula of hydrated magnesium sulphate crystals is MgSO4.xH2O. When 3.8 g of the hydrated crystals are heated, 2.00 g of anhydrous magnesium sulphate are produced. What is the value of x ?
(Relative atomic masses : H = 1.0, O = 16.0, Mg = 24.0, S = 32.0)
A. 3B. 4C. 5D. 6
Directions : Q.20 and Q.21 refer to the following experiment on a thermometric titration.
A sulphuric acid solution is titrated against 25.0 cm3 of 3.0 M sodium hydroxide solution. The results of the thermometric titration can be represented by the following graph :
20. The concentration of the sulphuric acid solution is
A. 1.00 MB. 1.25 MC. 2.50 MD. 5.00 M
21. Which of the following statement(s) is/are correct ?
(1) The temperature rises from X to Y because the reaction between sulphuric acid solution and sodium hydroxide solution is exothermic.
(2) The temperature drops from Y to Z because water is formed in the reaction between the sulphuric acid solution and sodium hydroxide solution.
(3) Z corresponds to the end point of the titration
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
22. Which of the following statements concerning 25.0 cm3 of 0.1 M hydrochloric acid and 25.0 cm3 of 0.1 M ethanoic acid is/are correct ?
(1) They contain the same number of hydrogen ions.(2) They require the same volume of 0.1 M sodium hydroxide solution for complete
neutralization.(3) They react with excess zinc granules at the same rate.
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
23. Concentrated sulphuric acid turns blue litmus paper red and then black. On the basis of these colour changes, which of the following deductions concerning concentrated sulphuric acid are correct ?
10 20 30 40 50 0
temp.
X
Y
Z
(1) It contains H+(aq) ions
(2) It is an oxidizing agent(3) It is a dehydrating agent
A. (1) and (2) onlyB. (1) and (3) onlyC. (2) and (3) onlyD. (1), (2) and (3)
24. The molecular formula of a gaseous element X is X2. If the relative atomic mass of X is 19, what is the number of molecules in 114 g of the gas ?
(Avogadro's number = 6.02 1023)
A. 3B. 6C. 3 6 1023
D. 6 6 1023
25. 0.12 g of sodium metal is added to a large volume of water. When the reaction is completed, the resulting solution is treated with 0.2 M hydrochloric acid. What is the volume of the acid required, to nearest cm3, for complete neutralization ?
(Relative atomic mass : Na = 23)
A. 13B. 26C. 39D. 52
26. 0.01 mol of C2H5OH is burnt completely in oxygen. What are the numbers of moles of carbon dioxide and water formed respectively ?
carbon dioxide water
A. 0.01 0.03B. 0.02 0.03C. 0.02 0.06D. 0.04 0.06
27. Which of the following gases, each having a mass of 10.0 g , has greatest number of molecules at room temperature and pressure ?
(Relative atomic masses : C = 12.0; N = 14.0; O = 16.0; F = 19.0; Ne = 20.2)
A. nitrogenB. fluorineC. neonD. carbon monoxide
28. When 2 moles of oxygen gas are collected at the anode during the electrolysis of dilute sulphuric acid, the number of moles of electrons released at anode is
A. 2B. 4C. 6D. 8
29. Which of the following substances react with concentrated sulphuric acid ?
(1) sulphur(2) sodium nitrate(3) hydrated copper(II) sulphate
A. (1) and (2) onlyB. (1) and (3) onlyC. (2) and (3) onlyD. (1), (2) and (3)
30. When sulphur dioxide is bubbled into sodium hydroxide solution for a long time, the final product is
A. sodium sulphiteB. sodium sulphateC. sodium hydrogensulphiteD. sodium hydrogensulphate
Directions : Q.31 and Q.32 refer to the following experiment :
A student measured the conductivity of a certain acid. When he added barium hydroxide solution dropwise to the acid, he found that the conductivity of the acid gradually dropped to almost zero.
31. The acid is probably
A. hydrochloric acidB. sulphuric acidC. nitric acidD. ethanoic acid
32. Which of the following reasons accounts for the change in the conductivity of the acid ?
A. Barium hydroxide is a weak electrolyteB. The acid is a weak electrolyteC. The neutralization reaction between barium hydroxide solution and the acid is
exothermicD. A precipitate is formed when barium hydroxide solution is added to the acid
33. Solution X is 45 cm3 of 1.2 M HCl and Solution Y is 60 cm3 of 0.9 M CH3COOH.
Which of the following statements concerning X and Y is correct ?
A. X has a higher pH value than YB. Both X and Y need the same volume of 1 M NaOH for neutralizationC. Both X and Y have the same electrical conductivityD. Y has a faster rate of reaction with marble chips than X
34. After 50 cm3 of 0.6 M H2SO4 have completely neutralized 100 cm3 of 0.6 M NaOH, the concentration of the resulting sodium sulphate solution is
A. 0.2 MB. 0.3 MC. 0.6 MD. 1.2 M
35. Which of the following can be used to distinguish between dilute hydrochloric acid and dilute nitric acid ?
(1) copper(2) silver nitrate solution(3) sodium hydrogencarbonate solution
A. (2) onlyB. (1) and (2) onlyC. (1) and (3) onlyD. (2) and (3) only
36. 2.60 g of a metal X combine 1.20 g of oxygen to form an oxide in which the oxidation number of X is +3. What is the relative atomic mass of X ?
(Relative atomic mass : O = 16.0)
A. 11.6B. 34.7C. 52.0D. 104
37. Which of the following graphs represents what would be obtained from the thermometric titration of 2 M hydrochloric acid with potassium hydroxide solution ?
A.
temp.
volume of KOH(aq) added0
B.
temp.
volume of KOH(aq) added0
C.
temp.
volume of KOH(aq) added0
D.
temp.
volume of KOH(aq) added0
38. What volume of water should be added to 100 cm3 of 2 M hydrochloric acid to change the acid concentration to 0.2 M ?
A. 100 cm3
B. 500 cm3
C. 900 cm3
D. 1000 cm3
39. When concentrated sulphuric acid is added to hydrated copper(II) sulphate crystals, which of the following would be observed ?
A. The crystals dissolve to form a blue solutionB. The crystals change to a white solidC. The crystals change to a black solidD. There is no observable change
40. 22 g of calcium carbonate are allowed to react with 200 cm3 of 0.5 M hydrochloric acid until no further reaction occurs. What is the mass of calcium carbonate left behind ?
(Relative atomic masses : C = 12.0; O = 16.0; Ca = 40.0)
A. 2 gB. 5 gC. 12 g
D. 17 g
41. What is the number of moles of Fe3+ ions in 0.1 dm3 of 0.5 Fe2(SO4)3 solution ?
A. 0.1 0.5B. 2 0.1 0.5C. 0.1 0.5 6 1023
D. 2 0.1 0.5 6 1023
42. 1.55 g of a hydrated sodium carbonate, Na2CO3.xH2O, react completely with 25 cm3 of 1 M hydrochloric acid. What is the value of x ?
(Relative atomic masses : H = 1.0; C = 12.0; O = 16.0; Na = 23.0)
A. 1B. 2C. 4D. 10
43. Which of the following gases contain the same number of molecules at 300 cm3 of oxygen under the same temperature and pressure ?
(1) 150 cm3 of NH3
(2) 200 cm3 of O3
(3) 300 cm3 of He(4) 300 cm3 of HCl
A. (1) and (2) onlyB. (3) and (4) onlyC. (1), (3) and (4) onlyD. (2), (3) and (4) only
44. Which of the following statements about hydrogen chloride is/are correct ?
(1) It forms dense white fumes with ammonia gas(2) It dissolves in methylbenzene to form H+ and Cl- ions(3) It turns dry litmus paper red
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
45. Which of the following contains the largest number of ATOMS at room temperature and
pressure ?
(Relative atomic masses : H = 1.0; N = 14.0; Cl = 35.5; Molar volume of gas at room temperature and pressure = 24.0 dm3)
A. 2 mol of ammonia gasB. 3 mol of nitrogen gasC. 7 g of hydrogen gasD. 90 dm3 of hydrogen chloride gas
46. The molecular formula of a gas is X3. If the Avogadro Number is L mol-1, how many molecules are there in 96 g of X3 ?
(Relative atomic mass of X = 16.0)
A. 12 L
B. 2 LC. 3 LD. 6 L
47. If 2 g of carbon dioxide gas contain x molecules, how many molecules are present in 2 g of helium gas ?
(Relative atomic masses : He = 4.0; C = 12.0; O = 16.0)
A. xB. 5 1
2 xC. 7 xD. 11 x
48. What volume of 0.5 M sulphuric acid is required to liberated 4.8 dm3 of carbon dioxide at room temperature and pressure from excess solid sodium hydrogencarbonate ? (Molar volume of gas at room temperature and pressure = 24.0 dm3)
A. 0.2 dm3
B. 0.4 dm3
C. 2.0 dm3
D. 4.0 dm3
49. 150.0 cm3 of 3.0 M sodium hydroxide solution is mixed with 50.0 cm3 of 1.0 M sodium hydroxide solution. The concentration of the resultant solution is
A. 2.0 MB. 2.5 MC. 3.3 MD. 4.0M
50. A pupil, working with dilute acids in the laboratory, carelessly poured the unused acids into the sink. Later it was found that the copper pipe in the sink had begun to leak. Which of the following acids is/are most likely to have caused the damage ?
(1) dilute nitric acid(2) dilute sulphuric acid(3) dilute hydrochloric acid
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
51. Which of the following statements concerning 25 cm3 of 1M hydrochloric acid and 25 cm3 of 1M ethanoic acid is/are correct ?
(1) They give the same colour change when the same quantity of universal indicator is added
(2) They react with marble chips at the same rate when the initial temperatures are the same
(3) They require the same number of moles of sodium hydroxide for complete neutralization
A. (1) onlyB. (3) onlyC. (1) and (2) onlyD. (2) and (3) only
52. Sulphuric acid is NOT used to prepare carbon dioxide from limestone because
A. the reaction between sulphuric acid and limestone is reversibleB. the reaction between sulphuric acid and limestone is too vigorousC. sulphuric acid is a strong oxidizing agentD. an insoluble product is formed which stops further reaction
53. Zinc does NOT liberate hydrogen from a 0.5 M nitric acid solution because
A. zinc is an unreactive metalB. nitric acid is an oxidizing agentC. the concentration of hydrogen ions in the nitric acid is too lowD. a layer of oxide film is formed on the surface of zinc to prevent further reaction
54. Gas X is bubbled steadily into solution Y shown in the set-up below :
In which of the following cases will NO observable change occur in solution Y ?
Gas X Solution Y A. sulphur dioxide bromine water
B. sulphur dioxide calcium hydroxideC. carbon dioxide bromine waterD. carbon dioxide calcium hydroxide
55. 16.1 g of a hydrated metal sulphate was heated to constant mass. After cooling to room temperature, the residual anhydrous metal sulphate weighed 7.1 g. How many moles of water crystallization are there in one mole of the hydrated metal sulphate ?
(Relative molecular masses : anhydrous metal sulphate = 142.0; water = 18.0)
A. 4B. 5C. 7D. 10
56. Nitric acid can be prepared by heating concentrated sulphuric acid with a metal nitrate because nitric acid is
A. volatileB. monobasicC. a strong acidD. an oxidizing agent
57. If dilute hydrochloric acid gets into a student’s eye during experiment, the first thing the student should do is to
A. dial 999 for helpB. was the eye with waterC. wash the eye with dilute ammonia solutionD. wash the eye with dilute sodium hydroxide solution
58. 100 cm3 of a gas X2 react completely with 150 cm3 of oxygen to form 100 cm3 of a gaseous oxide. If all measurements are made at room temperature and pressure, the formula of the gaseous oxide is
A. XO2
B. X2OC. X2O3
D. X3O2
59. If there are y molecules in 8 g of oxygen, how many molecules are present in 40 g of sulphur trioxide ?
A. y4
B. y2
C. yD. 2y
60. When 250 cm3 of 2.00 M hydrochloric acid are added to 13.0 g of zinc, the volume of gas produced at room temperature and pressure is
A. 2.40 dm3
B. 4.80 dm3
C. 6.00 dm3
D. 12.0 dm3
(Relative atomic masses : H = 1.00; Cl = 35.5; Zn = 65.0; Molar volume of a gas at room temperature and pressure = 24.0 dm3)
61. 25 cm3 of a 0.2 M solution of an acid requires 15 cm3 of 0.5 M sodium carbonate solution for complete neutralization. What is the basicity of the acid ?
A. 1B. 2C. 3D. 4
62. If a glass reagent bottle containing sodium hydroxide solution is allowed to stand in air for a few weeks, it is often difficult to remove the glass stopper due to the formation of a solid round the bottle neck. The solid is probably
A. sodium oxideB. sodium peroxideC. sodium carbonateD. sodium hydrogencarbonate
63. Which of the following compounds has the highest basicity ?
A. HClB. HCOOHC. H2SO4
D. CH3COOH
64. 500 cm3 of calcium hydroxide solution contains 3.7 g of calcium hydroxide. What is the molarity of the solution ? (Relative atomic masses : H = 1.0, O =16.0, Ca = 40.1)
A. 0.05 MB. 0.10 MC. 0.13 MD. 0.26 M
65. Which of the following samples of gases contains the smallest number of molecules ? (Relative atomic masses : H = 1.0, C = 12.0, N = 14.0, O = 16.0, S = 32.1)
A. 10 g of NO2
B. 10 g of CO2
C. 10 g of H2SD. 10 g of C2H4
66. Which of the following statements concerning 20 cm3 of 1 M CH3COOH and 10 cm3 of 1 M H2SO4 is correct ?
A. They have the same pH values.B. They have the same electrical conductivity.C. They react with magnesium at the same rate.D. They require the same number of moles of sodium hydroxide for complete
neutralization.
67. NaHCO3 decomposes upon heating to form Na2CO3, CO2 and H2O. What is the volume of CO2 formed at room temperature and pressure if 336 g of NaHCO3 undergoes complete decomposition ?
A. 12 dm3
B. 24 dm3
C. 48 dm3
D. 96 dm3
68. Methane burns completely in oxygen according to the following equations :
CH4 + 2O2 CO2 + 2H2O
What is the mass of oxygen required for the complete combustion of 4.8 g of methane ? (Relative atomic masses : H = 1.0, C = 12.0, O = 16.0)
A. 48 gB. 96 gC. 192 g
D. 384 g
Directions : Questions 69 – 71 refer to the following information.
In an experiment to determine the concentration of sulphuric acid in a brand of toilet cleaner, 25.0 cm3 of the cleaner was first diluted to 250.0 cm3 with distilled water. Upon titration with 0.950 M sodium hydroxide solution using phenolphthalein as indicator, 25.0 cm3 of the diluted cleaner required 27.1 cm3 of the sodium hydroxide solution to reach the end point.
69. Which of the following types of apparatus should be used to measure 25.0 cm3 of the toilet cleaner ?
A. pipetteB. buretteC. measuring cylinderD. volumetric flask
70. What is the colour change at the end point of the titration ?
A. from colourless to pinkB. from pink to colourlessC. from yellow to redD. from red to yellow
71. What is the concentration of sulphuric acid in the undiluted toilet cleaner ?
A. 1.29 MB. 2.58 MC. 5.15 MD. 10.3 M
72. Which of the following statements concerning 1 mole of aluminium is/are correct ? (Avogadro’s constant = 6.02 1023 ; Molar volume of gas at room temperature and pressure =
24 dm3)
(1) It can form 1 mole of Al3+ ions.(2) It can form 3 6.02 1023 of Al3+ ions.(3) It occupies 24 dm3 at room temperature and pressure.
A. (1) onlyB. (2) onlyC. (1) and (3) onlyD. (2) and (3) only
1st statement 2nd statement
73. The volume of hydrogen liberated at 10 M hydrochloric acid is a
room temperature and pressure by the reaction between 10 cm3 of 10 M hydrochloric acid and excess zinc granules is greater than that between 50 cm3 of 2 M hydrochloric acid and excess zinc granules.
stronger acid than 2 M hydrochloric acid.
74. The basicity of ethanoic acid is four. One molecule of ethanoic acid contains four atoms of hydrogen.
75. If a student accidentally spilled some hydrochloric acid on his hand, he should immediately wash his hand with sodium hydroxide solution.
Sodium hydroxide solution can neutralize hydrochloric acid.
76. At room temperature and pressure, the molar volume of oxygen gas is greater than that of hydrogen gas.
The relative atomic mass of oxygen is greater than that of hydrogen.
77. 100 cm3 of 1 M hydrochloric acid reacts with excess magnesium ribbon at the same rate as 100 cm3 of sulphuric acid.
Both acids contains the same concentration of H+
(aq) ions.
78. A solution of hydrogen chloride in methylbenzene can turn blue litmus paper red.
Hydrogen chloride dissolves in methylbenzene to form hydrogen ions.
79.
80.
81.
When concentrated sulphuric acid is poured onto a piece of cotton cloth, the piece of cloth becomes charred.
Citric acid is an electrolyte.
2 M hydrochloric acid reacts faster with 1 g of zinc granules than with 1 g zinc powder.
Concentrated sulphuric acid is a strong oxidizing agent.
When citric acid is dissolved in water, citric acid molecules become mobile.
The surface area of 1 g of zinc powder is larger than that of 1 g of zinc granules.
SOLUTION :
1. B. 11. B. 21. A. 31. B. 41. B. 51. B. 61. C. 71. C.
2. B. 12. D. 22. B. 32. D. 42. A. 52. D. 62. C. 72. A.
3. C. 13. B. 23. B. 33. B. 43. B. 53. B. 63. C. 73. D.
4. B. 14. D. 24. C. 34. A. 44. A. 54. C. 64. B. 74. C.
5. B. 15. A. 25. B. 35. B. 45. A. 55. D. 65. D. 75. C.
6. A. 16. B. 26. B. 36. C. 46. B. 56. A. 66. D. 76. C.
7. C. 17. C. 27. C. 37. C. 47. D. 57. B. 67. C. 77. D.
8. B. 18. D. 28. D. 38. C. 48. A. 58. C. 68. C. 78. D.
9. D. 19. D. 29. D. 39. B. 49. B. 59. D. 69. A. 79. B.
10. B. 20. B. 30. C. 40. D. 50. A. 60. B. 70. A. 80. B.
81. C.