WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

CHAPTER 7: ACIDS AND BASES

A ACIDS AND BASES

Learning OutcomesYou 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)

HCl (aq) → . . .…….(aq) + Cl- (aq)

……… (aq) → H+ (aq) + NO3 - (aq)

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Basesc)

d)

H2SO4 (aq) → ……. …… + ………..

CH3COOH (aq) …………. + CH3COO- (aq)

(Refer to page 117 -118 - F4 Chemistry textbook)

Activity 2 :

Fill in the blanks with correct words:

1 A base is a substance that reacts with an acid to form ...................................................only.

An alkali is a water-soluble base which ionises in water to produce………..………..........,OH-

2 Complete the table below

Name of alkali Formula of alkali

(i) Sodium hydroxide

(ii) KOH

(iii) Ammonia aqueous

3 Complete the ionization of following alkalis :

NaOH (aq) → …….(aq) + OH- (aq)

……… (aq) + H2O (l) NH4+ (aq) + …………. (aq)

4 Uses of acids, bases and alkalis

(a) To use as …………………. … reagent

Example: sodium hydroxide solution, sulphuric acid, hydrochloric acid

(b) To ..................................................................................................... ……………

Example: Ethanoic acid (vinegar), benzoic acid

(c)To make various ………………..

Example: Magnesium oxide antacid medicine, Ascorbic acid vitamin C

(d)To produce …………., detergent and ………………

Example: sodium hydroxide to make soap and detergent

Magnesium hydroxide added to tooth-paste

(e)To manufacture dyes,……………………. and drugs

Example: methylamine

(f)Used in rocket fuel

Example:…………………………………………………………………………………………

(Refer to page 118 - F4 Chemistry textbook)

Activity 3: Role of water and its properties of acids and alkalis

Fill in the blanks with correct words.

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

1 An acid only shows its …………..…… properties when dissolve in ……………………….

2 In the presence of water, the acid ionises to form ……………………………………..ions .

3 Without water, an acid still exists as…………………and there are no ................ ions present.

4 Glacial Ethanoic acid, CH3COOH is an example of acidic substance.

Complete the following table to show the role of water in acidic properties.

Condition of ethanoic acid Effect on the blue litmus paper

Inference

Glacial ethanoic acid,

Ethanoic acid in water

Ethanoic acid in dry propanone ( 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 ………………… properties

7 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 in water)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 alkalisTick (√ )

Statement True or False1. All acids are dangerous

2. All alkalis are dangerous

3. Acids taste sweet

4. Alkalis taste bitter

5. Acids taste sour

6. Most acids can burn skin

7. Alkalis feel soapy

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases8. Acids produce H+ ions in solution

9. Acids produce OH- ions in solution

10. Acids can corrode

11. Acids have a pH above 7

12. Acids have a pH below 7

13. Alkalis turn moist red litmus paper blue

14. 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.

……………………………………………………………………………………………………...

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.

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

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.

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)

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

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 a solution.

2 pH value less than 7 , indicates an…………………………solution

pH value equal to 7 , indicates a…………………………solution

pH value more than 7 , indicates an…………………………solution

3 pH value can be determined by using………….................,pH paper or…………………indicator.

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

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

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases 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

Examples

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WAJA F4 Chemistry 2010 Chapter 7: Acids and BasesC: CONCENTRATIONS OF ACIDS AND ALKALIS

Learning Outcomes You 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 1dm 3 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 the concentration 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 cm3 solution that contains 50 g dm-3 ?

[Answer: 10 g]

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Concentration in ................... Concentration in............................ X Molar mass

÷ Molar mass

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases(Refer to page 123 -124 - F4 Chemistry textbook )

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 mol dm-3]

Activity 11The number of moles of solute, n in a given volume of solution V and the molarity of M can be calculated 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 sulphuric acid, H2SO4.

[Answer: 0.2 mol of H+ ions]

Activity 12 : Preparation of Standard solutions

1 What is a standard solution?

……………………………………………………………………………………………………

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n = MV

n = M x V 1000

n = MV 1000 or

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases2 Preparation of standard solutions by Weighing method (mass of solute) :-

Step 1 : Calculate the mass of solute needed .

mass = n X molar mass

= MV X molar mass 1000

Example: To prepare 100 cm 3 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 mass 1000

= 2.0 X 100 X 40 = 8 g 1000Try this: (a) To prepare 250 cm 3 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 dissolving x g of sodium hydroxide in 750 cm3 of water. What is the value of x ? [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 bottle or small beaker and filter funnel to ensure no solute remains in any of the apparatus used.

Transfer the dissolved solute into a suitable volumetric flask.

(a)

Add water slowly by using a dropper to bring the level of the solution to the calibration mark.

The volumetric flask is closed tightly and inverted several times to get a uniform or homogenous solution.

(b)

Calculate the mass of solute needed.

Weigh out the exact mass of solute needed in a weighing bottle.

Dissolved the solute in a small

(c)

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n = MV 1000

n = mass molar mass

WAJA F4 Chemistry 2010 Chapter 7: Acids and Basesamount of distilled water.

Add more water carefully to the volumetric flask and swirl gently.

Shake well to ensure thorough mixing.

(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 dilution M2 = molarity of solution after dilution V2 = 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 cm 3 of 0.5 mol dm -3 potassium manganate(VII) ,KMnO 4 solution is prepared from 1.0 mol dm -3 potassium manganate(VII) ,KMnO 4 solution. Calculate the volume of the solution

[Answer : 50 cm3] Step 2

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

(b)

Add water slowly by using a dropper to bring the level of the solution to the calibration mark.

The volumetric flask is closed tightly and inverted several times to get a uniform or homogenous solution.

Transfer the stock solution to a suitable volumetric flask.

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M1V1 = M2V2

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

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

(c)

(d)

Calculate the volume of stock solution required.

Use a pipette to draw up the required volume 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 hydrogen dissociation 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 OutcomesYou 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

……………………………………………………………………………………………12

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases(b) sulphuric acid and sodium hydroxide

……………………………………………………………………………………………(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.

Indicator Colour in solution Acid Neutral Alkali

Red litmus paperBlue litmus paperPhenolphthaleinMethyl orange

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

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WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

(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 moles M = Molarity of solutionV = Volume of solution in dm3

Ma = molarity of acidMb = molarity of alkaliVa = volume of acidVb = volume of alkali

a 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 concentration required 26.50 cm3 of 1.0 mol dm-3 sulphuric acid, H2SO4 for complete reaction in titration. Calculate the molarity of sodium hydroxide.

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MaVa = a MbVb

bn = MVn = mass

molar mass mass

WAJA F4 Chemistry 2010 Chapter 7: Acids and BasesWrite out a balanced chemical equation:

H2SO4 + 2NaOH Na2SO4 + 2H2O a = 1 mol b = 2 molMaVa 1 MbVb = 2 , 1.0 X 26.50 = 1Mb 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 neutralise 30.00 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 completely with 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

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1

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases(b) g dm-3

[Answer (a) 0.06 mol dm-3 (b) 5.88 g dm-3]5 What is the molarity of phosphoric acid if 15 cm3 of the acid is neutralized by 38.5 cm3 of 0.15

mol dm-3 NaOH ?

[Answer (a) 0.218 mol dm-3]

Activity 18

1 A student carried out an experiment to determine the end-point for the titration of 25.0 cm3 of 1.0 mol dm-3 sodium hydroxide solution with hydrochloric acid. Phenolphthalein is used as the acid-base indicator. Table 1 shows the three titrations that were conducted and the magnification of the burette readings.

Titration No. I II III

Initial burette reading

1 2

…………………..

13

14

……………….

26

27

………………..

16

hydrochloric acid

hydrochloric acid

hydrochloric acid

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

Final burette reading

13

14

……………………

26

27

……………………

38

39

…………………….

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 mol dm-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 acids into strong acids and weak acids.

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hydrochloric acid hydrochloric

acid hydrochloric acid

WAJA F4 Chemistry 2010 Chapter 7: Acids and Bases

(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 the

colour change.

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

sodium hydroxide.

………………………………………………………………………………………………….

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Ethanoic acid, hydrochloric acid, sulphuric acid,

carbonic acid, nitric acid,

Strong acids Weak acids