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CHAPTER 8: SALT
ANSWERS
Activity 1
1. ionic compound, hydrogen , acid , metal , ammonium
2.
Acid Formula of acid Salt Formula Cation Anion
Hydrochloric acid HCl Sodium chloride NaCl Na+ Cl-
Carbonic acid H2CO3 Potassium carbonate K2CO3 K+ CO3
2-
Sulphuric acid H2SO4 Copper(II) sulphate CuSO4 Cu2+ SO4
2-
Nitric acid HNO3 Ammonium nitrate NH4NO3 NH4+ NO3-
Nitric acid HNO3 Magnesium nitrate Mg(NO3)2 Mg2+ NO3
-
Ethanoic acid CH3COOH Sodium ethanoate CH3COONa Na+ CH3COO
-
2. ( any other correct answer can be accepted)
Salt Uses
Barium sulphate BaSO4 X-ray meals in hospital
Calsium sulphate CaSO4 Plaster of Paris for broken bone
Iron sulphate FeSO4 Iron tablets for anaemia patient
Ammonium nitrate NH4NO3 Nitrogenous fertilizer
Copper(II) sulphate CuSO4 Fungicide
Sodium chloride NaCl A flavouring agent
Sodium hydrogen carbonate Baking powder
Sodium nitrite NaNO2 For preserving food/ food preservative
Sodium hypochlorite NaOCl Bleaching agent
Tin(II) fluoride SnF2 Toothpaste
Lead(II) chromate PbCrO4 Paint for yellow line on road
Activity 2
1. sodium, potassium and ammonium.
2. nitrate
3. lead(II), barium and calcium sulphate
4. lead(II), argentums and mercury(I) chloride
5. sodium, potassium and ammonium carbonate
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CHAPTER 8: SALT
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No Formula of
Salt
Solubility ( , X ) No Formula of Salt Solubility ( , X )
1 PbCO3 X 21 MgCO3 X
2 NaCl 22 KCl 3 CaSO4 X 23 (NH 4)2SO4 4 AgNO3 24 Cu(NO3)2 5 K2CO3 25 SnCO3 X6 FeCl 3 26 CaCl 2 7 Na2SO4 27 BaSO4 X8 NH4NO3 28 KNO3 9 CuSO4 29 Ag 2CO3 X10 PbCl 2 X 30 MgCl 2 11 ZnCO3 X 31 ZnSO4 12 Ca(NO3)2 32 Ba(NO3)2 13 Na2CO3 33 FeCO3 X14 AgCl X 34 NH 4Cl 15 PbSO4 X 35 Fe(NO3)3 16 Pb(NO3)2 36 MgSO4 17 (NH 4)2CO3 37 BaCO3 X18 HgCl 2 X 38 ZnCl 2 19 Na2SO4 39 FeSO4 20 NaNO3 40 Mg(NO3)2
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CHAPTER 8: SALT
Activity 3
1. a. metal + acid salt + hydrogen
b. metal oxide (or metal hydroxide) + acid salt + water
c. alkali + acid salt + water
e. metal carbonate + acid salt + carbon dioxide + water
2. a. Mg + H2SO4 MgSO4 + H2
b. (i) CuO + 2HCl CuCl2 + H2O
(ii) Zn(OH)2 + 2HNO3 Zn(NO3)2 + 2H2O
c. NaOH + HCl NaCl + H2Od. MgCO3 + H2SO4 CaSO4 + CO2 + H2O
3.
Method of Preparation Reactants Salt Formed Other
Product
a) metal + acid Magnesium + hydrochloric
acid
Magnesium chloride Hydrogen
b) metal oxide + acid Copper(II) oxide + sulphuricacid
Copper(II) sulphate water
c) metal carbonate +
acid
Zinc carbonate + sulphuric
acid
Zinc sulphate Water +
carbon
dioxide
d) metal hydroxide +
acid
Potassium hydroxide + nitric
acid
Potassium nitrate Water
e) alkali + acid Sodium hydroxide +
hydrochloric acid
Sodium chloride Water
4.
(a) Copper(II) sulphate : Copper(II) oxide / hydroxide / carbonate + sulphuric acid
(b) Zinc chloride : Zinc / (zinc oxide / hydroxide / carbonate) + hydrochloric acid
(c) Potassium nitrate : potassium hydroxide + nitric acid
(d) Ammonium sulphate : aqueous ammonia + sulphuric acid
(e) Magnesium nitrate : Magnesium / (magnesium oxide / hydroxide / carbonate) +
nitric acid
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CHAPTER 8: SALT
5. a. Mg(s) + 2H+(aq) Mg2+(aq) + H2 (g)
b. MgO(s) + 2H+(aq) Mg2+(aq) + H2O (l)
c. OH-(aq) + H+(aq) H2O (l)
d. CuCO3(s) + 2H+(aq) Cu2+(aq) + CO2(g) + H2O (l)
Activity 4
Name of solution : sodium hydroxide and hydrochloric acid
Chemical equation : NaOH + HCl NaCl + H2O
Procedure :
1. A pipette is used to transfer 25.0 3cm of sodium hydroxide solution to a conical flask. 2 to 3
drops of phenolphthalein is added.
2. A burette is filled with hydrochloric acid and record the initial burette reading.
3. Titration is carried out carefully by slowly adding the acid into the conical flask and the flask is
shaken well.
4. The acid is added continuously until the indicator turns from pink to colourless. The final burette
reading is recorded.
5. The volume of acid used to neutralize 25.0 3cm of the alkali is determined. (let the volume be V
3cm )
6. 25.0 3cm of the same sodium hydroxide solution is pipetted into a conical flask. No indicator is
addeded.
7. From the burette, exactly V 3
cmof hydrochloric acid is added to the alkali and is shaken well.
8. The contents of the conical flask is poured into an evaporating dish.
9. The solution is heated gently to evaporate most of the water to produce a saturated solution.
10. The hot saturated salt solution is cooled for crystallization to occur.
11. The sodium chloride crystals is filtered, and the salt is rinsed with a little distilled water.
12. The crystals are dried by pressing them between filter papers
Salt crystal characteristic
Flat surfaces, straight edges and sharp angles
Fixed geometrical shape
Fixed angles between two neighbouring surfaces
Crystals of some substance have same hapes but maybe in different sizes
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CHAPTER 8: SALT
Activity 5
Name of chemical : copper(II) oxide and sulphuric acid
Chemical equation : CuO + H2SO4 CuSO4 + H2O
Procedure :
1. 50 3cm of sulphuric acid 1 mol dm-3 is poured into a beaker. The acid is warmed.
2. By using a spatula, copper(II) oxide powder is added bit by bit into the acid. The mixture is stirred
well.
3. Copper(II) oxide is added continuously until some of it no longer dissolves.
4. The unreacted copper(II) oxide is removed by filtration
5. The filtrate is filtered into an evaporating dish. The solution is heated gently to produce a
saturated salt solution.
6. The saturated solution is cooled until crystals are formed.
7. The copper(II) nitrate crystals are filtered, and are then rinsed with a little distilled water.
8. The crystals are dried by pressing them between filter papers
9. Purification process Recrystallisation
The copper(II) sulphate crystals are placed in a beaker.
Enough distilled water is added to cover the crystals. The solution is gently heated and stirred
with a glass rod. Water is added bit by bit until all the crystals are dissolved.
Impurities is removed by filtration and filtrate is poured into an evaporating dish.
The solution is heated gently to evaporate most of the water to produce a saturated solution.
The hot saturated salt solution is cooled for crystallization to occur.
The copper(II) nitrate crystals are filtered, and the salt is rinsed with a little distilled water.
The crystals are dried by pressing them between filter papers
Activity 6
1. Precipitation, double decomposition reaction, ions , precipitate
2. Example 1: Barium sulphate,4
BaSO
Solution 1: Barium chloride/nitrate Solution 2: sodium/potassium sulphate
Chemical equation : BaCl2 + Na2SO4 BaSO4 + 2NaCl
Ionic Equation : Ba2+ + SO42- BaSO4
Example 2: Copper carbonate, CuCO3
Solution 1: copper(II) nitrate/sulphate/chloride Solution 2: Sodium/potassium carbonate
Chemical equation : Cu(NO3)2 + Na2CO3 CuCO3 + 2NaNO3
Ionic Equation : Cu2+ + CO32- CuCO3
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CHAPTER 8: SALT
Observation : green precipitate formed
Example 3: Lead(II) chromate(VI), 4PbCrO
Solution 1: lead(II) nitrate Solution 2: Sodium/potassium chromate(VI)
Chemical equation : Pb(NO3)2 (aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)
Ionic Equation : Pb2+ (aq) + CrO42- (aq) PbCrO4 (s)
Observation : yellow precipitate formed
Activity 7
Name of solution : lead(II) nitrate and Sodium/potassium iodide
Chemical equation : Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)
Procedure :
1. 50 cm3 of 0.5 mol dm-3 lead(II) nitrate solution is poured into 50 cm3 of 1.0 mol dm-3
potassium iodide in a beaker
2. The mixture is stirred with a glass rod
3. A yellow precipitate of lead(II) iodide is formed immediately
4. The resulting mixture is then filtered
5. The yellow precipitate is rinsed with distilled water to remove impurities
6. The yellow solid, lead(II) iodide is then pressed between a few pieces of filter papers to be
dried
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CHAPTER 8: SALT
Activity 8
Test Tube 1 2 3 4 5 6 7
Volume of Pb(NO3)2 /cm3 5.0 5.0 5.0 5.0 5.0 5.0 5.0
No of mole of Pb(NO3)2 0.0025
Volume of K2CrO4 /cm3 1.0 2.0 3.0 4.0 5.0 6.0 7.0
No of mole of K2CrO4 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035
Height of precipitate / cm 0.45 0.90 1.40 1.90 2.30 2.30 2.30
Colour of the solution
above the precipitate
Colourless Yellow
(b)
(c) (i) 5 cm3
(ii) 0.0025 mole of chromate(VI) ions that has reacted with 0.0025 mole of Pb 2+. ions.
1 mole of chromate(VI) ions that has reacted with 1 mole of Pb2+. ions.
(iii) PbCrO4
(iv) ionic equation : Pb2+ + CrO42- PbCrO4
(d) The height increase from test 1 to 5 and become constant from test tube 5 to 7.
(e) In test tube 1-4, there are excess lead(II) ions, so more precipitate are formed when
increasing volume of CrO42- solution added. In test tube 5-7 all the lead(II) ions had reacted
with chromate(VI) ions, so the amount of precipitate formed is the same.
Activity 9 : Solve problems involving calculation of quantities of reactants or product in
stoichiometric reactions
1 (a) Zn + 2HCl ZnCl2 + H2
(b) No of mole of HCl = 2.0 x 50 = 0.1 mol
1000
7
Volume of potassium chromate(VI) / cm3
Height of precipitate / cm
1 2 3 4 5 6 7
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CHAPTER 8: SALT
(c) Mole ratio HCl : H2 = 2 : 1
No of mole of H2 = 1/2 x 0.1 = 0.05 mol
Volume of H2 = 0.05 x 24 dm3
= 1.2 dm3
2 (a) No of mole of H2SO4 = 1.0 x 100 = 0.1 mol
1000
(b) Mole ratio H2SO4 : MgSO4 = 1 : 1
No of mole of MgSO4 = 0.1 mol
Mass of MgSO4 = 0.1 x (24 + 32 + 4x16) g
= 12.0 g
3.a) No of mole of Mg = 0.12 = 0.005
24
No of mole of MgCl2 = 0.005
Mass of MgCl2 = 0.005 x (24 + 2 x 35.5)
= 0.475 g
b) No of mole of H2 = 0.005 mole
Vol of H2 = 0.005 x 24 dm3
= 0.12 dm3 or 120 cm3
4. (a)AgNO3 + NaCl AgCl + NaNO3
(b)
Number of moles of AgNO3 = 1.0 x 50 = 0.05 mol
1000
Mole ratio of AgNO3 : NaCl = 1 : 1
Number of mole of NaCl = 0.5 x z = 0.05 mole
1000
Z = 0.05 x 1000 = 100 cm3
0.5
b) Number of mole of AgCl = Number of moles of AgNO3 = 0.05 mol
Mass of AgCl = 0.05 x (108 + 35.5) g
= 7.175 g
Activity 10 : Qualitative Analysis
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CHAPTER 8: SALT
1. ions, physical and chemical properties.
2.
Colour (solid or solution) Substance or cation or anion
Green powder CuCO3 , Fe2+
Blue powder Cu2+
Brown powder Fe3+
Black powder CuO, MnO2
Yellow powder when hot and white when cold ZnO
Brown powder when hot and yellow when cold PbO
Blue solution Cu2+
Pale green solution Fe2+
Brown solution Fe3+
Solid : White
Solution : colourless
Cation : Ca2+ , Al3+ , Mg2+ , Pb2+ , Zn2+ ,
NH4+
Solid : White
Solution : colourless
Anion : Cl- , CO32- , SO42-, NO3-
3. Complete the following table
Salts Solubility in water Colour
Lead(II) chloride, silver chloride, barium
sulphate, lead(II) sulphate and calcium
sulphate
Insoluble white
Copper(II) carbonate Insoluble green
Iron(II) sulphate soluble green
Iron(III) salts except carbonate Soluble Brown
Lead(II) sulphate Insoluble white
Magnesium carbonate Insoluble white
Zinc chloride soluble white
Ammonium carbonate soluble white
Lead(II) iodide / chromate(VI) Insoluble Yellow
Activity 11 : Confirmatory Tests for gases,
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Activity 12 : Action of Heat On Carbonate Salts
Carbonate salt Action of heat
Magnesium carbonate MgCO3 MgO + CO2
Observation : White solid formed. Gas liberated turn lime water
chalky
Aluminium carbonate Al2(CO3)3 Al2O3 + 3CO2
Observation : White solid formed. Gas liberated turn lime water
chalky
Zinc carbonate ZnCO3 ZnO + CO2
Observation : The residue is yellow when hot and white when
cold. Gas liberated turn lime water chalky
Lead(II) carbonate PbCO3 PbO + CO2
Observation : The residue is brown when hot and yellow whencold. Gas liberated turn lime water chalky
Copper(II) carbonate CuCO3 CuO + CO2
Observation : Black solid formed. Gas liberated turn lime water
chalky
Activity 13 : Action of Heat On Nitrate Salts
Nitrate salts Action by Heat
Sodium nitrate 2NaNO3 2 NaNO2 + O2
Observation : white solid formed, gas released relighted glowing
splinter
Magnesium
nitrate
2Mg(NO3)2 2MgO + 4NO2 + O2
Observation : white solid formed, Brown gas which turns moist blue
litmus red released. Another gas released relighted
glowing splinter
Zinc nitrate 2Zn(NO3)2 2ZnO + 4NO2 + O2
Observation : The residue is yellow when hot and white when cold.,
Brown gas which turns moist blue litmus red released.
Gas ObservationCarbon dioxide lime water turn milky/chalky
Oxygen glowing splinter will be relightedNitrogen dioxide Brown gas, blue litmus paper change to red
Chlorine Greenish yellow gas The colour of litmus paper change from blue
red
whiteAmmonia white fume formedRed litmus paper change to blue.
Hydrogen 'pop' sound is heardHydrogen chloride white fume formed
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CHAPTER 8: SALT
Another gas released relighted glowing splinter
Lead(II) nitrate 2Pb(NO3)2 2PbO + 4NO2 + O2
Observation : The residue is brown when hot and yellow when cold,
Brown gas which turns moist blue litmus red released.
Another gas released relighted glowing splinter
Copper(II) nitrate 2Cu(NO3)2 2CuO + 4NO2 + O2
Observation : black solid formed, Brown gas which turns moist blue
litmus red released. Another gas released relighted
glowing splinter
Activity 14 : Confirmatory Tests for Anions,
1. Ionic equation : 2H+ + CO32- H2O + CO2
Ionic equation : Ag+ + Cl- AgClIonic equation : Ba2+ + SO42- BaSO4
2. Which anion produce the following results?
Salt K1 sulphate ion
Salt K2 chloride ion
Salt K3 nitrate ion
Salt K4 carbonate ion
Activity 15 : Reaction of Cations with alkali solution
1.
NaOH solution Ammonia Solution NH3
A little In excess A little In excess
Soluble ( , X ) Soluble ( , X )Ca2+ White precipitate X No change Zn2+ White precipitate White precipitate Al 3+ White precipitate White precipitate XPb 2+ White precipitate White precipitate XMg2+ White precipitate X White precipitate X
Cu 2+ Blue precipitate X Blue precipitate X
Fe 2+ Green precipitate X Green precipitate X
Fe 3+ Brown precipitate X Brown precipitate X
2. Salt K5 - Inference 1 ammonium ion
Inference 2 Zinc, aluminium and lead(II) ions
Inference 3 magnesium or calcium ions
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CHAPTER 8: SALT
Salt K6 Inference 4 calcium ion
Inference 5 Zinc ion
Inference 6 magnesium , aluminium and lead(II) ions
Activity 16 : C onfirmatory Tests for Fe2+, Fe3+, Pb2+ and NH4+
(A)Cation Name of Reagent Observation
+2Pb Potassium iodide solution Yellow , dissolve , reappear
+2Fe Potassium hexacyanoferrate(III) Dark blue
+3Fe Potassium thiocyanate solution Blood red solution
NH4+ Nessler reagent Brown
(b) Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test
tubes respectively. Then add a few drops of potassium hexacyanoferrate(II) solution to two
test tubes, Fe2+ ions solution will form light blue precipitate whereas Fe3+ ions solution will
form dark blue precipitate [All correct to score 1 mark, can use any other reagent]
or
Pour 2 cm3 of iron(II) sulphate solution and 2 cm3 of iron(III) chloride solution into two test
tube respectively. Then add a few drops of potassium thiocyanate solution to two test tubes,
there is no change in Fe2+ ions solution whereas Fe3+ ions solution will form blood red
solution.
Activity 17 : Structured qualitative analysis to identify salts
(A). Identify the salt S1
Test Inference
Step 1. Nitrogen dioxide gas, oxygen gas released.
Residue is lead(II) oxide
2 Fe2+, Fe3+ or Cu2+ ions may not be present
(a) Zn2+ , Al3+ or Pb2+ ions may be present
(b) Pb2+ or Al3+ ion may be present
(c) Confirm lead(II), Pb2+ ions present
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CHAPTER 8: SALT
(d) Confirm nitrate , NO3- ions present
Salt S1 is lead(II) nitrate
(B). Identify the salt S2
Test Inference
1. Zn2+ , Al3+ or Pb2+ ions may be present
2. Zn2+ ions may be present
3. Cl- ions not present
4. SO42- ions may be present
. Conclusion for salt S2 : zinc sulphate
Activity 18 : plan qualitative analysis to identify anions
All answers must be correct to score one mark for each chart.
CHART A: SODIUM CARBONATE AND SODIUM NITRATE
13
Test 1
Add dilute 3HNO
(any acid)
Result 1Effervescence
Result 1
No change
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CHAPTER 8: SALT
CHART B: SODIUM CHLORIDE AND SODIUM SULPHATE
14
Test 2add dilute H2SO4 followedby FeSO4 solution.
Carefully add 1 3cm of
concentrated H2SO4
Test 3
Add dilute 3HNO ,followed by silver nitrate,
3AgNO solution
Test 4Add dilute HCl, followed
by barium chloride,BaCl2 solution
SODIUMC
A
RBONATE
SODIUMN
ITRATE
Result 2
No change
Result 3
No change
Result 4No change
Result 2
Brown ring
Result 3
No change
Result 4
No change
Test 1
Add dilute 3HNO(any acid)
Result 1
No change
Result 1
No change
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CHAPTER 8: SALT
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Test 2add dilute H2SO4 followedby FeSO4 solution.
Carefully add 1 3cm of
concentrated H2SO4
Test 3
Add dilute 3HNO ,
followed by silver nitrate,3
AgNO solution
Test 4Add dilute HCl, followed by
barium chloride,BaCl2 solution
SODIUM
CHLORIDE
SODIUM
SULPHATE
Result 2
No change
Result 3White
precipitate
Result 4
No change
Result 2
No change
Result 3No change
Result 4
Whiteprecipitate