7 acids and bases ed 2010 exercise

7/27/2019 7 Acids and Bases Ed 2010 Exercise

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

CHAPTER 7: ACIDS AND BASES

A ACIDS AND BASES

Learning Outcomes

You should be able to: State the meaning of acid, base and alkali

State uses of acids, bases and alkalis in daily life

Explain the role of water of water in the formation of hydrogen ions to show the properties of

acids

Explain the role of water in the formation of hydroxide ions to show the properties of alkalis

Describe chemical properties of acids and alkalis

Activity 1 Meaning of acid ,base and alkali

Fill in the blanks with the correct words:

1 An acid is a chemical substance which ionises in. to produce .ions.

The hydrogen ion combines with a water molecule, H2O to form a .. ion,

H3O+.2 Acid can be classified as a.acid or a .acid based on its

basicity.3 Basicity is the number of ionisable . atoms per molecule of an acid.4 A base is a substance that reacts with an acid to form a ... and . only.

Bases include metal hydroxides and metal oxides.5 Give the names of acids, their formulae and its basicity:

Name of acid Formula of acid Basicity(i) Hydrochloric acid(ii) H2SO4(iii) HNO3(iv) Ethanoic acid

6 Complete the ionization of acids below :

a)

b)

c)

d)

HCl(aq) . . ..(aq) + Cl- (aq)

(aq) H+(aq) + NO3 -(aq)

H2SO4(aq) . + ..

CH3COOH(aq) . + CH3COO-(aq)(Refer to page 117 -118 - F4 Chemistry textbook)

Activity 2 :

Fill in the blanks with correct words:

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( organic solvent )

5 An alkali only shows its .. properties when dissolve in ..6 In the presence of water, the base dissociates to produce ... ions that

are responsible for the properties7 Ammonia,NH3 is an example of alkali.

Complete the table below to show the role of water in alkaline properties.Condition of ammonia Effect on the red litmus paper InferenceDry

Aqueous (dissolved inwater)Dissolved in propanone,(organic solvent)

(Refer to page 118 -119 F4 Chemistry textbook and page 84 86 F4 Chemistry Practical Book )

Activity 4: Properties of acids and alkalis

Tick ( )Statement True or False

1. All acids are dangerous2. All alkalis are dangerous3. Acids taste sweet4. Alkalis taste bitter5. Acids taste sour6. Most acids can burn skin7. Alkalis feel soapy

8. Acids produce H+ ions in solution9. Acids produce OH- ions in solution

10. Acids can corrode11. Acids have a pH above 712. Acids have a pH below 713. Alkalis turn moist red litmus paper blue14. Acids turn moist red litmus paper blue

(Refer to page 119 - F4 Chemistry textbook and page 87 90 - F4 Chemistry Practical Book )

Activity 5 : Chemical properties of acids1 Acids react with bases to form salts and water only. Bases are metal oxides or metal hydroxide.

Write the chemical equation for the reaction between sulphuric acid and copper(II) oxide....

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2 Acids react with reactive metals to produce salts and hydrogen gas.

Write the chemical equation for the reaction between hydrochloric acid and zinc .

...3 Acids react with metal carbonates to produce salts, water and carbon dioxide gas.

Write the chemical equation for the reaction between nitric acid and calcium carbonate.

...

Activity 6 : Chemical properties of alkalis

1 Alkalis react with acids to form salts and water only

Write the chemical equation for the reaction between sodium hydroxide and benzoic acid.

...2 When a mixture of an alkali and an ammonium salt is heated, ammonia gas is liberated.

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Write the chemical equation for the reaction between sodium hydroxide and ammonium chloride .

...3 Alkalis react with most metal ion solutions ( cations ) to produce the insoluble metal hydroxides

or precipitate - (precipitation reaction)

Write the chemical equation for the reaction between sodium hydroxide and iron(II) sulphate.

...(Refer to page 120 - F4 Chemistry textbook and page 91- F4 Chemistry Practical Book )

B: The strength of acids and alkalis

Learning Outcomes:You should be able to:

State the use of a pH scale

Relate pH value with acidic or alkaline properties of a substance

Relate concentration of hydrogen ions with pH value

Relate concentration of hydroxide ions with pH value

Relate strong or weak acid with degree of dissociation

Conceptualise qualitatively strong and weak acids

Conceptualise qualitatively strong and weak alkalis

Activity 7: The pH scale

Fill in the blanks with correct words

1 The pH scale ( 0 to 14 ) , is used to indicate the degree of or . of asolution.

2 pH value less than 7 , indicates ansolutionpH value equal to 7 , indicates asolution

pH value more than 7 , indicates ansolution3 pH value can be determined by using.................,pH paper orindicator.4

Acids Neutral Alkalis0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

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Acidity ......................................(increase or decrease )

Alkalinity.........................(increase or decrease )

(Refer to page 121 Chemistry text book)

Activity 8 : Strong and weak acid1. Complete the flowchart below to understand the concept of strong acid and weak acid

Strong acid Weak acid

Degree of dissociation

Ionization in water

Concentration of ions

pH value

Examples

Activity 9: Strong and weak alkali

1. Complete the flowchart below to understand the concept of strong alkali and weak alkali.

Strong alkali Weak alkali

Degree of dissociation

Ionization in water

Concentration of ions

pH value

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Examples

C: CONCENTRATIONS OF ACIDS AND ALKALIS

Learning OutcomesYou should be able to:

State the meaning of concentration

State the meaning of molarity

State the relationship between the number of moles with molarity and volume of a solution

Describe the methods for preparing standard solutions

Describe the preparation of a solution with a specified concentration using dilution method

Relate pH values with the molarity of acids and alkalis

Solve numerical involving molarity of acids and alkalis

Activity 10 : Concentration of acids and alkalis

Fill in the blanks with the correct answers.

1

2

The concentration of a solution refers to the quantity of solute in 1dm3 of solution

Concentration can be defined in two ways :-

(a) Concentration in g dm-3 =

(b) Concentration in mol dm-3 =

(Concentration in mol dm-3 is also known as molarity or molar concentration (M ) )

2 The two units of concentration can be inter-converted:

Work this out.

3 5.0 g of copper(II) sulphate is dissolved in water to form 500 cm3

solution. Calculate theconcentration of copper(II) sulphate solution in g dm-3 ?

[Answer: 10.0 g dm-3]

4 What is the mass of sodium carbonate required to dissolve in water to prepare 200 cm3solution that contains 50 g dm-3 ?

[Answer: 10 g]

(Refer to page 123 -124 - F4 Chemistry textbook )

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Concentration in ................... Concentration in............................

X Molar mass

Molar mass


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5 4.0 g of sodium carbonate powder, Na2CO3 , is dissolved in water and made up to 250 cm3.What is the molarity of the sodium carbonate solution?[Relative atomic mass: C, 12; O, 16; Na, 23]

[Answer: 0.15 moldm-3]

Activity 11The number of moles of solute, n in a given volume of solution V and the molarity of M can becalculated by using the formula :

n = Number of moles of soluteM = Molarity of solution (mol dm-3)

V = Volume of solution (dm3)

If the volume is in cm3 convert the volume of solution from cm3 to dm3

5 Calculate the number of moles of ammonia in 150 cm3 of 2 mol dm-3 aqueous ammonia.

[Answer: 0.3 mol]6 A student pipetted 20.0 cm3 of potassium hydroxide , KOH solution into a conical flask. The

concentration of the alkali was 1.5 mol dm -3 . Calculate the number of moles of potassium ,KOH in the flask.

[Answer: 0.03 mol dm-3]

7 Calculate the number of moles of hydrogen ions present in 200 cm3 of 0.5 mol dm-3 sulphuricacid, H2SO4.

[Answer: 0.2 mol of H+ ions]

Activity 12 : Preparation of Standard solutions

1 What is a standard solution?

2 Preparation of standard solutions by Weighing method (mass of solute) :-

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n = MV

n = M x V

1000

n = MV

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Step 1 : Calculate the mass of solute needed .

mass = n X molar mass

= MV X molar mass1000

Example: To prepare 100 cm3 of 2.0 mol dm-3 sodium hydroxide solution.Calculate the mass of NaOH needed. [Relative atomic mass: Na, 23 ; O, 16 ; H, 1]

mass = n X molar mass

= MV X molar mass1000

= 2.0 X 100 X 40 = 8 g1000

Try this:(a) To prepare 250 cm3 of 1.0 mol dm-3 sodium carbonate solution.

Calculate the mass of Na2CO3 needed. [Relative atomic mass: Na, 23 ; O, 16 ; C, 12]

[Answer : 26.50g]

(b) 0.25 mol dm-3 solution of sodium hydroxide was prepared by dissolvingxg of sodiumhydroxide in 750 cm3 of water. What is the value ofx?[Relative atomic mass: Na, 23 ; O, 16 ; H, 1]

[Answer : 7.5 g]

(Refer to page 126 - F4 Chemistry textbook )

Step 2 :Match the descriptions / procedures with the correct diagram below.

Wash and rinse the weighing bottleor small beaker and filter funnel toensure no solute remains in anyof the apparatus used.

Transfer the dissolved solute into asuitable volumetric flask.

(a)

Add water slowly by using adropper to bring the level of thesolution to the calibration mark.

The volumetric flask is closedtightly and inverted several times toget a uniform or homogenoussolution.

(b)

Calculate the mass of soluteneeded.

Weigh out the exact mass of soluteneeded in a weighing bottle.

Dissolved the solute in a small

(c)

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n = MV

1000

n = mass

molar mass


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amount of distilled water.

Add more water carefully to thevolumetric flask and swirl gently.

Shake well to ensure thoroughmixing.

(d)

Activity 13 : Preparation of Standard solutions by Dilution method

1 Dilution method

Step 1 : Calculate the volume of stock solution required by using the equation:-

M1 = molarity of solution before dilution

V1 = volume of solution before dilutionM2 = molarity of solution after dilutionV2 = volume of solution after dilution

Example: 50 cm3 of 0.1 mol dm-3 sodium hydroxide, NaOH solution from 2.0 mol dm-3

sodium hydroxide,NaOH solution

Before dilution After dilutionM1 V1 M2 V2

2.0 mol dm-3 ? 0.1 mol dm-3 50 cm3

2.0 x V1 = 0.1 x 50

V1 = 0.1 x 50 = 2.5 cm3

2.0

Try this: 100 cm3 of 0.5 mol dm-3 potassium manganate(VII) ,KMnO4 solution is preparedfrom 1.0 mol dm-3 potassium manganate(VII) ,KMnO4 solution. Calculate the volume of thesolution

[Answer : 50 cm3] Step 2

Match the diagram with the correct descriptions below.(a)

(b)

Add water slowly by using a dropper tobring the level of the solution to thecalibration mark.

The volumetric flask is closed tightly andinverted several times to get a uniform orhomogenous solution.

Transfer the stock solution to a suitablevolumetric flask.

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M1V1 = M2V2

When using the equation M1V1 = M2V2 ,make sure that both V1 and V2 are ofthe same unit.


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(c)

(d)

Calculate the volume of stock solutionrequired.

Use a pipette to draw up the requiredvolume of stock solution.

Activity 14 : The pH values and molarity of acids and alkalisFill in the blanks with correct words . Use words given in the box.

Increases decreases concentration hydrogendissociation higher hydroxide alkali

1 The pH value of an acid or an alkali depends on three factors :

(a) degree of.

(b) molarity or ..

(c) .. of the acid or ..2 The lower the pH value, the .. the concentration of ions.

3 The higher the pH value, the .. the concentration of ... ions.

4 As the molarity of an acid increases , the pH value of the acid .

The pH value of an alkali increases when the molarity of the alkali ...(Refer to page 128 - F4 Chemistry textbook )

D : NEUTRALISATION

Learning Outcomes

You should be able:-

Explain the meaning of neutralisation.

Write equations for neutralisation

Explain the applications of neutralization in daily life

Describe the titration process of acid-base

Determine the end-point of titration during neutralization

Solve numerical problems involving neutralisation

Activity 15 : Neutralisation

1 What is the meaning of neutralisation?

..2 What are the only products of neutralisation?

.3 Write a balanced chemical equation for the neutralisation of the following reactions:-

(a) nitric acid and barium hydroxide

(b) sulphuric acid and sodium hydroxide

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(c) phosphoric acid and calcium hydroxide

(d) ethanoic acid and potassium hydroxide

4 Complete the flow chart below:-

(Refer to page 128 129 - F4 Chemistry textbook )

Activity 16 : Acid base Titration

1 What is a titration?

.2 What is the function of an indicator?

..3 Complete the table below.

IndicatorColour in solution

Acid Neutral Alkali

Red litmus paperBlue litmus paper

Phenolphthalein

Methyl orange

4 Write out the procedure for carrying out an acid-base titration to determine the volume ofnitric acid 0.5 mol dm-3needed to neutralise 25 cm3 potassium hydroxide 0.5 mol dm-3 .Label the diagram.

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(Refer to page 130 F4 Chemistry textbook and Page 103 F4 - Chemistry Practical Book)

Activity 17 : Numerical problems involving neutralisation

Useful equations in solving numerical problems involving neutralisation.:

n = no of molesM = Molarity of solutionV = Volume of solution in dm3

Ma = molarity of acidMb = molarity of alkali

Va = volume of acidVb = volume of alkalia and b = mole ratio of acid to alkali in a balanced chemical equation

Example:In an experiment, 25 cm3 of sodium hydroxide solution, NaOH of unknown concentrationrequired 26.50 cm3 of 1.0 mol dm-3 sulphuric acid, H2SO4 for complete reaction in titration.Calculate the molarity of sodium hydroxide.

Write out a balanced chemical equation:

H2SO4 + 2NaOH Na2SO4 + 2H2Oa = 1 mol b = 2 mol

MaVa 1MbVb = 2

,1.0 X 26.50 = 1

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MaVa = a

MbVbn = MVn = mass

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Mb X 25.00 2

Mb = 2 X 1.0 X 26.50 = 2.12 mol dm-3 (Molarity of sodium hydroxide)25.00

1 What is the volume of 1.5 mol dm-3 aqueous ammmonia required to completely neutralise30.00 cm3 of 0.5 mol dm-3 sulphuric acid ?

2NH3 + H2SO4 (NH4 ) 2SO4

[Answer: 20 cm3]

2 Calculate the volume in cm3 2.0 mol dm-3 hydrochloric acid that is required to react completelywith 2.65 g of sodium carbonate.[Relative atomic mass: Na, 23 ; O, 16 ; C, 12]

[Answer: 25 cm3]

3 25 cm3 of sulphuric acid was neutralised with 18.0 cm3 of sodium hydroxide 1.0 moldm-3. Calculate

(a) the number of moles of sulphuric acid that is used in this reaction.(b) the molarity of sulphuric acid

[Answer (a) 0.009 mol (b) 0.36 mol dm-3]

4 24 cm3 of 0.1 mol dm-3 NaOH is required to completely neutralise 20.0 cm3 of sulphuric acid.Calculate the concentration of sulphuric acid in(a) mol dm-3

(b) g dm-3

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Final burettereading

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.

Table 1

(a) Record the burette readings for the three titrations in the space provided in Table 1.

(b) Construct a table and record the initial burette reading, final burette reading and thevolume of acid used for each titration.

(c) Calculate the average volume of hydrochloric acid used in the experiment.

(d) Calculate the concentration of hydrochloric acid used in the experiment.

(e) If the experiment is repeated by replacing 1.0 mol dm-3 of hydrochloric acid with 1.0 moldm-3 of sulphuric acid, predict the end-point of the titration.

.

(f) Acids can be classified into strong acid and weak acid. Classify the following acidsinto strong acids and weak acids.

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Ethanoic acid, hydrochloric acid, sulphuric acid,

carbonic acid, nitric acid,

Strong acids Weak acids


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(g) State the colour change of the phenolphthalein indicator at the end point of titration.

(h) If phenolphthalein is replaced with methyl orange as the acid-base indicator, state thecolour change.

(i) Write a chemical equation for the neutralisation reaction between hydrochloric acid and

sodium hydroxide.

.

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7 acids and bases ed 2010 exercise

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