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MARKING SCHEME - ACIDS AND BASES

ACTIVITY ANSWERS

1 Refer to page 117 118 - F4 Chemistry book

2 Refer to page 118 - F4 Chemistry book

3 Refer to page 118 119 - F4 Chemistry book and page 84 86 - F4 Chemistry

Practical book41 2 3 4 5 6 7 8 9 10 11 12 13 14

F F F T T T T T F T F T T F

5 Refer to page 119 - F4 Chemistry textbook and page 87 - 90 Chemistry Practicalbook

6 Refer to page 120 - F4 Chemistry textbook and page 91 Chemistry Practical book

7 Refer to page 121 - F4 Chemistry textbook

8 No.1 Strong acid Chracteristic Weak acid

high Degree of dissociation lowcompletely Ionization of water partially

high Concentration of ions low

1 - 3 pH value 4 - 6

HCl/HNO3/H2SO4 Examples CH3COOH

2 (a) HNO3(aq) H+(aq) + NO3

-(aq)

(b)H2SO4(aq) 2H+(aq) + SO4

2-(aq)(c) HCl (aq) H

+ (aq) + Cl- (aq)

(d)CH3COOH (aq) H+ (aq) + CH3COO-(aq)9 1 Strong alkali Chracteristic Weak alkali

high Degree of dissociation lowcompletely Ionization of water partially

high Concentration of ions low11 - 14 pH value 8 - 9

NaOH/KOH Examples Aq. ammonia,NH3

2 (a) NaOH (aq) Na+(aq) + OH

-(aq)(b)KOH (aq) K

+(aq) + OH-(aq)

(c) NH3 + H2O (l) NH4+(aq) + OH- (aq)

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concentration

(a) mass of solute(g)Volume of solution(dm3)

(b) no. of mole of solute(mol)Volume of solution(dm3)

molarity , g dm-3

12 1 Standard solution a solution in which its concentration is accurately known

5 (a) Calculate the mass of solute needed.

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

Dissolved the solute in a small amount of distilled water.

(b) Wash and rinse the weighing bottle ,small beaker and filter funnel to

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8/8/2019 7A Acids and Bases- Answer

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ensure no solute remains in any of the apparatus used.

Transfer the dissolved solute into a suitable volumetric flask.

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

Shake well to ensure thorough mixing.

(d) 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.

13 3 (a) Calculate the volume of stock solution required.

(b) Use a pipette to draw up the required volume of stock solution.

(c) Transfer the stock solution to a suitable volumetric flask.

(d) Add water slowly by using a dropper to bring the level of thesolution to the calibration mark.

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

14 Refer to page 128 - F4 Chemistry textbook

15 3 (a) 2HNO3 + Ba(OH)2(aq) Ba(NO3)2(aq) + H2O (aq)

(b) H2SO4 + 2NaOH (aq) Na2SO4(aq) + 2H2O (aq)(c) 2H3PO4 + 3Ca(OH)2(aq) Ca3(PO4)2(aq) + 6H2O (aq)(d) CH3COOH + KOH (aq) CH3COOK4(aq) + H2O

(aq)

4 Refer to page 128 - 129 - F4 Chemistry textbook

16 3Indicator

Colour in solution of:Acid Alkali

Red litmus paper red blue

Blue litmus paper blue red

Phenolphthalein colourless pink

Methyl orange red yellow

4 Refer to page 103 - F4 Chemistry Practical book

18 1(a) Initial burette readings: 0.80 cm3

, 13.40 cm3

, 25.90 cm3

Final burette readings : 13.40 cm3, 25.90 cm3, 38.40 cm3

(b) Titration No. I II II

Initial burette reading/cm3 0.80 13.40 25.90

Final burette reading/cm3 13.40 25.90 38.40

Volume of acid used/cm3 12.60 12.50 12.50

(c) Volume of acid used = 12.60 + 12.50 + 12.503

= 12.50 cm3

(d) 2 mol dm-3

(e) 6.25 cm3

(f) Strong acids: hydrochloric acid, phosphoric acid, nitric acid

Weak acids: ethanoic acid, carbonic acid(g) Pink to colourless

(h) Yellow to red

(i) HCl + NaOH NaCl + H2O

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