Chemistry Paper 3 Form 3 End Term 2 Exams 2021 with Marking Schemes
INSTRUCTIONS TO CANDIDATES
- Answer all questions on the space provided
- All working Must be clearly shown
- You are provided with;
- Solution A 0.2MNaOH
- Solution B Hydrochloric acid
- Solution C sodium Carbonate solution
You are required to standardize hydrochloric acid using solution A and hence determine the morality in moles per liter of solution C sodium carbonate
Procedure I
Using a pipette transfer 25cm3 solution A into conical flask add 2 to 3 drops phenolphthalein indicator then titrate with hydrochloric acid provided in a beaker from burette. Shake the conical flask after each additional and note the volume required to neutralize sodium hydroxide solution. Record your results in the table below.- What is the average volume of solution B? (5mks)
- Calculate the number of moles of solution B required to complete neutralize solution A. (3mks)
- Calculate the molarity in moles per liter of solution B hydrochloric acid. (1mk)
Procedure II
Rinse the pipette thoroughly then pipette 25cm3 of solution C sodium carbonate into clean conical flask then add 2 to 3 drops of phenolphthalein indicator. Refill the burette with solution B and use it to titrate content of the conical flask. Shake the flask after each addition of the acid solution B and note the volume of the acid required to neutralize 25cm3 of sodium carbonate solution C.
Record your results in table below- Calculate average volume of solution B used. (5mks)
- Calculate the number of moles of solution C in 25cm3 of the solution. (2mks)
- Calculate the molarity of solution C in Mole per liter. (1mk)
- You are provided with solid D. Carry out tests below and record your observation and inferences in the table below.
- Describe the appearance of sold D. (2mks)
- Take a boiling tube, add all solid D and add about 10cm3 of distilled water. Shake the mixture
Observations Inference (1mk) (1mk) - Divide the solution obtained above into five portions. To the first portion add drops of lead (ii) Nitrate solution.
Observations Inference (1mk) (2mks) - To the second portion add 3 drops of barium Nitrate.
Observations Inference (1mk) (1mk) - To the third portion add few then excess drops of ammonia solution.
Observations Inference (1mk) (2mk) - To the fifth portion, add drops of hydrochloric acid then boil the mixture.
Observations Inference (2mk) (1mk) - Give the formula of the anion acid cation present in substance D.
Cation…………………………………… (1mk)
Anion ……………………………………. (1mk)
Confidential
- Solution A – 0.2M NaOH
- 80cm3 per students - Solution B – 0.2MHCl
- 150cm3 per student - Solution C – 0.05M Na2CO3
- 80 cm3 per student - Solid D (0.5g Pb(NO3)2)
- Burette
- Pipette
- Complete stand
- 3 conical flask
- Access – Phenolphthalein indicator and a dropper
-0.1M pb(NO3)2 and a dropper
-2M NH4OH
-0.5M Ba(NO3)2 and a dropper
-0.5M HCl and a dropper - 6 test tubes in rack
- 1 boiling tube
- Wash bottle with distilled water
Marking Scheme
-
- CT✓
D✓
A±0.1✓
±0.2✓½
PA✓
FA✓
Average = 25.1cm3 - Moles of NaOH = 25.0 x 0. 2
1000
= 0.005moles✓
Moles of acid, moles ratio 1:1✓
= 0.005 x 1
= 0.005moles✓ -
0.005 x 1000 ✓½25
= 0.2M ✓½ - Volume average = 12.5cm3
CT✓
A±0.1✓
± 0.2✓½
D✓
PA✓
FA✓ - Moles of the acid = 12.5 x 0.2
1000
= 0.0025moles✓
Moles of carbonate, moles ratio 1:2✓½
= 0.0025/2 = 0.00125 moles ✓½ - = 0.00125 x 1000
25
=0.05M
- CT✓
-
-
White/ colorless✓
Crystalline solid✓ -
Observations Inference Solid dissolved forming a colorless solution ✓ (1mk) Soluble salt ✓
Absence of colored ions (1mk) -
Observations Inference No white precipitate
(1mk)
(2mks) -
Observations Inference No white precipitate
(1mk)
(1mk) -
Observations Inference White precipitate
Insoluble in excess
(1mk)
(2mks) -
Observations Inference No effervescence
White precipiatate that dissolve on boiling
(1mk)Pb2+ present
(1mk) -
Cation Pb2+ (1mk)
Anion NO3- (1mk)
Assumption
The only soluble salts of lead is Lead (II)Nitrate
-
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