INSTRUCTIONS TO CANDIDATES
- Answer all the Questions in the spaces provided.
- You are not allowed to start working with the apparatus for the first 15 minutes of the 2 ¼ hours allowed for this paper. This time is to enable you to read the Question paper and make sure you have all the chemicals and apparatus you need.
- All working must be clearly shown where necessary.
- Mathematical tables and electronic calculators may be used.
Question 1
You are provided with the following:
- Solution A ; Hydrochloric acid
- Solution B; 0.03M sodium hydroxide
- Solution C, Containing 15.74g of Na2CO3. XH2O in 250ml of the solution.
You are required to determine: -
- The concentration of solution A
- The value of X in the carbonate Na2CO3. XH2O
PROCEDURE A
- Fill the burette with solution A. Using clean pipette, place 25.0cm3 of solution B into a 250ml conical flask.
- Add 2 drops of phenolphthalein indicator and titrate with solution A. Record your results in table I below. Repeat the experiment two more times and complete the table.
Table I (4mks)
I II III Final burette reading (cm3) Initial burette reading (cm3) Volume of solution A (cm3) used
- Determine the :-
- Average volume of solution A used. (1mk)
- Number of moles of sodium hydroxide in 25 cm3 of solution B used. (1mk)
- Number of moles of acid in volume of solution A used. (1mk)
- Concentration of solution A in moles per litre. (1mk)
PROCEDURE B- Using a clean pipette, place 25.0 cm3 of solution C into a 250ml volumetric flask. Add about 100cm3 of distilled water. Shake well and add more distilled water to make up to the mark. Label this solution D
- Fill the burette with solution A. Using a clean pipette, place 25 cm3 of solution D into a conical flask. Add 2 drops of methyl orange indicator and titrate with solution A. Record your results in the table II.
- Repeat the titration two more times and complete table II.
Table II (4mks)
I II III Final burette reading (cm3) Initial burette reading (cm3) Volume of solution A (cm3) used
- Determine the: -
- Average volume of solution A used. (1mk)
- Moles of the acid of solution A that reacted with the carbonate solution D. (1mk)
- Number of moles of the carbonate in 25 cm3 of solution D used. (1mk)
- Number of moles of carbonate in 250cm3 of solution D (1mk)
- Concentration of carbonate solution C in moles per litre. (1mk)
- Concentration of the carbonate solution C in grams per litre. (1mk)
- Value of X in Na2CO3. XH2O (H=1.0, C=12.0, O=16.0 Na=23.0) (1mk)
Question 2
You are provided with solid M. Use it to carry out the tests below. Write the observations and inferences in the space provided.
- Place solid M in a boiling tube and add about 10cm3 of distilled water. Divide the resulting solution into five portions
Observation Inference (1 mk) 1 (mk) - To the first portion add sodium hydroxide solution dropwise till excess.
Observation Inference (1 mk) 1 (mk) - To the second portion add aqueous ammonia solution dropwise till excess.
Observation Inference (1 mk) 1 (mk) - To the third portion add 3 drops of sodium chloride solution.
Observation Inference (1 mk) 1 (mk) - To the fourth portion add about 2cm3 of HNO3 acid.
Observation Inference (1 mk) 1 (mk) - To the fifth portion add 3 drops of lead (II) nitrate solution and warm.
Observation Inference (1 mk) 1 (mk)
Question 3
You are provided with solid G. Use it to carry out the tests below. Write the observations and inferences in the space provided.
- Using a clean metallic spatula, take one third of solid G and place on Bunsen burner flame.
Observation Inference (1 mk) 1 (mk) - Place the remaining solid G in a boiling tube. Add 10cm3 of distilled water and shake the mixture until all the solid dissolves. Divide the resulting solution into four portions.
To the first portion add 3 drops of acidified potassium manganate (vii)
Observation Inference (1 mk) 1 (mk) - To the second portion add 3drops of bromine water
Observation Inference (1 mk) 1 (mk) - To the fourth portion dip universal indicator paper and determine the pH of the solution
Observation Inference (1 mk) 1 (mk) - To the third portion add solid sodium hydrogen carbonate
Observation Inference (½ mk) ½ (mk)
CONFIDENTIAL
INSTRUCTIONS
In additional to the apparatus and fittings common in a chemistry laboratory, each candidate will require the following.
- About 150ml of solution labelled A.
- About 100ml solution labelled B.
- About 50ml of solution labelled C
- About 0.2g of sodium hydrogen carbonate in a stoppered container.
- About 0.5g of solid M in a stoppered container.
- About 0.5g of solid G in a stoppered container
- 0 – 50ml burette.
- 25ml pipette.
- Two 250ml conical flasks
- 250ml volumetric flask
- 10ml measuring cylinder.
- Six test tubes on a test tube rack.
- A boiling tube.
- test tube holder.
- Complete stand.
- A white tile.
- One metallic spatula.
- Distilled water in a wash bottle.
- One label
Access to:
- Source of heat.
- Universal indicator paper and its pH chart.
- 2M aqueous ammonia supplied with a dropper.
- 2M aqueous sodium hydroxide supplied with a dropper.
- Pb(NO3)2(aq) supplied with a dropper
- Acidified potassium manganate (VII) supplied with a dropper.
- Bromine water supplied with a dropper.
- 2M dilute nitric (V) acid.
- Methyl orange indicator with a dropper
- Phenolphthalein indicator with a dropper
- Sodium chloride solution
NB:
- Solution A is prepared by dissolving 4.cm3 of concentrated HCl (1.18g/cm3 ) to 500cm3 of water and dilute to 1 litre.
- Solution B is prepared by dissolving 1.2g of NaOH pellets in about 600ml of distilled water and diluting to 1 litre.
- Solution C is prepared by dissolving 62.9g of Na2CO3 .10H2O in about 800ml of distilled water and then topping up to 1 litre.
- Acidified potassium permanganate is prepared by dissolving 3.5g of KMnO4(s) in 200cm3 of 2M H2SO4(aq) and toping up to one litre solution.
- 2M H2SO4(aq) is prepared by diluting 110cm3 of concentrated Sulphuric (VI) acid to make one litre of solution.
- 2M NaOH (aq) is prepared by dissolving 80g of NaOH pellets in one litre of solution.
- 2M HNO3 is prepared by adding 128cm3 of Conc. HNO3 to about 500ml of water and dilute to 1 litre.
- Sodium chloride solution is prepared dissolving 5.85g of NaCl in 1 litre of water
- Lead (II) nitrate solution is prepared by dissolving 30g of Pb(NO3)2 in 1litre of water
- Solid M is aluminium sulphate
- Solid G is maleic acid.
MARKING SCHEME
Question 1
Procedure A
PROCEDURE II
Table I
Titration |
I |
II |
III |
Final burette readings ( cm3) |
15.0 |
15.0 |
15.0 |
Initial burette reading ( cm3) |
0.0 |
0.0 |
0.0 |
Volume ]of solution R used ( cm3) |
15.0 |
15.0 |
15.0 |
- Complete table C.T. 1mk
- Decimal point D.P 1mk
- Accuracy AC 1mk
- Principle averaging P.A 1mk
- Final Accuracy FA 1mk
5mks
Complete table………………………………………………….(1 Mark)
Conditions
- penalize ½ mk for inversion
- penalize ½ mk for unrealistic reading of less than 0.1 and above 50
- penalize ½ mk for wrong arithmetic
N/B penalize once only for ANY or ALL the above.
Decimal place …………………………………………………..(1 Mark)
- All readings must be recorded to at least one decimal place used consistently or 2 decimal places used consistently.
- If 2 decimal places are used then the second decimal place Must be a zero or a five otherwise penalize fully.
Accuracy ……………………………………………………….. (1 Mark)
- If any of the titre values is within ± 0.1 of school value award 1mk
- If any of the titre values is within ± 0.2 of school value award ½ mk or otherwise penalize fully
Principle of averaging ………………………………………….. (1 Mark)
N/B – Only consistent values should be averaged
- The values averaged must be shown
- The averaged value should be recorded to at least 2dp unless it works out to exactly a whole number or 1 dp.
Final answer
- If the averaged value is within ± 0.1 of the school value – award 1mk
- If the average value is outside ± 0.1 but within ± 0.2 – award ½ mk
- If averaging is not done but there are consistent values average for the candidate credit accordingly.
( ii) Number of moles of NaOH, solution B used. ( 1mk)
mols = 0.03 ×25 =0.00075mols
1000
(iii) Moles of acid solution A used in the reaction (1 mk)NaOH : HCl is 1:1 thus mols of HCl=0.00075mols
(iv) concentration of acid solution A in mols/litre. ( 1mk)
molarity of soln A = 0.00075 ×1000
average titre
PROCEDURE B
Table II
Titration |
I |
II |
III |
Final burette readings ( cm3) |
22.0 |
22.0 |
22.0 |
Initial burette reading ( cm3) |
0.0 |
0.0 |
0.0 |
Volume ]of solution R used ( cm3) |
22.0 |
22.0 |
22.0 |
- Complete table C.T 1mk
- Decimal point D.P 1mk
- Accuracy A C 1mk
- Principle averaging P.A 1mk
- Final Accuracy FA 1mk
5mks
Complete table………………………………………………….(1 Mark)
Conditions
- penalize ½ mk for inversion
- penalize ½ mk for unrealistic reading of less than 0.1 and above 50
- penalize ½ mk for wrong arithmetic
N/B penalize once only for ANY or ALL the above.
Decimal place …………………………………………………..(1 Mark)
- All readings must be recorded to at least one decimal place used consistently or 2 decimal places used consistently.
- If 2 decimal places are used then the second decimal place Must be a zero or a five otherwise penalize fully.
Accuracy ……………………………………………………….. (1 Mark)
- If any of the titre values is within ± 0.1 of school value award 1mk
- If any of the titre values is within ± 0.2 of school value award ½ mk or otherwise penalize fully
Principle of averaging ………………………………………….. (1 Mark)
N/B – Only consistent values should be averaged
- The values averaged must be shown
- The averaged value should be recorded to at least 2dp unless it works out to exactly a whole number or 1 dp.
Final answer
- If the averaged value is within ± 0.1 of the school value – award 1mk
- If the average value is outside ± 0.1 but within ± 0.2 – award ½ mk
- If averaging is not done but there are consistent values average for the candidate credit accordingly.
(b)(ii) Moles of solution A that reacted with solution D ( 1mks)
mols = Molarity of soln A × average titre
1000
(iii) Moles of solution D used in the reaction ( 1mk)
Reacting ratio of Na2CO3 : HCl is 1:2 thus moles of D
mols = mols of HClsoln A used
2
(iv) Moles of solution D present in 250ml. ( 1mk)
mols = mols in (iii) above × 250
25
(v) Concentration of carbonate soln C in moles per litre ( 1mks)
molarity = mols in (iv) above ×1000
250
(vi) Concentration of carbonate soln C in grams per litre ( 1mks)
mols = 15.74×1000 = 62.96g/l
250
(vii) Value of X in Na2CO3. XH2O. (H=1.0, C=12.0, O=16.0 Na=23.0) (1mk)
Question 2
Solid M is aluminium sulphate, Al2SO4
i)
|
Dissolves to form a colourless solution ✓ 1 |
Soluble salt ✓ 1 or Cu2+, Fe2+, Fe3+ absent ✔½ |
ii |
white ppt which dissolves in excess NaOH ✓ 1 |
Pb 2+, Al 3+, Zn 2+ present ✓ 1 |
iii |
Forms a white ppt insoluble in excess NaOH ✓ 1 |
Pb 2+, Al 3+ present ✓ 1 |
iv |
No white precipitate is formed ✓ 1 |
Al 3+ present ✓ 1 |
v |
No effervescence/no bubbles ✓ 1 |
CO32-, HCO3-, SO32- absent ✓ 1 |
vi |
white precipitate insoluble on warming ✓ 1 |
SO42- present ✓ 1 |
Question 3
Solid G is maleic acid.
a |
Melts and burns with a yellow sooty flame ✓ 1 |
\ / C = C or –C ≡ C- present ✓ 1 / \ |
b |
Purple KMnO4 is decolourised✓ 1 |
\ / C = C , –C ≡ C- or R –OH present ✓ 1 / \ |
c |
Yellow bromine water is decolurised ✓ 1 |
\ / C = C or –C ≡ C- present ✓ 1 / \ |
d |
Accept pH= 2 to 3 ✓ 1 |
Strongly acidic substance |
e |
Effervescence occurs / bubbles are produced ✔½ |
H+ , - COOH present ✔½ |
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