Instructions:
- Answer ALL questions
- 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 will enable you read through the question paper and make sure you have all the chemicals and apparatus required.
- Mathematical tables and electronic calculators may be used
- All working must be clearly shown where necessary.
FOR EXAMINER’S USE ONLY.
|
Question |
Maximum score |
Candidate’s score |
|
1 |
20 |
|
|
2 |
12 |
|
|
3 |
8 |
|
|
Total score |
40 |
QUESTIONS
- You are provided with:
- Solution A of Potassium manganate (VII).
- 05M solution B of oxalic acid.
- Solution C containing 4.9g of ammonium iron (II) Sulphate, (NH4)2 SO4.FeSO4.6H2O, in 250cm3 of water.
- You are required to:
- Determine the rate of reaction between oxalic acid and Potassium manganate (VII).
- Standardize the solution A.
PROCEDURE I:
Using a measuring cylinder, place 1 cm3 of solution A into each of the five (5) test-tubes in a rack. Clean the measuring cylinder and use it to place 19cm3 of solution B into a boiling tube. Prepare a water bath by placing about 200cm3 of water into a beaker and start to heat. Place a thermometer into solution B and place it in the warm water until it attains a temperature of 40oC. Remove the boiling tube from the water-bath and place it in the test-tube rack. Add the first portion of solution A immediately and at the same time start a stop watch. Record the time taken of solution A to be decolourised in table I below. Repeat the procedure at temperatures of 50oC,60oC,70oC and 80oC to complete the table.
|
Temperature of solution B (oC) |
40 |
50 |
60 |
70 |
80 |
|
Time taken for decolourisation (tsecs) |
|||||
|
I/t sec-1 |
(3 marks)
- Plot a graph of 1/t against temperature (X-axis) (3 marks)
- From the graph determine the time taken for the mixture to decolourise at 65oC (2 marks)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….
iii) How does the rate of reaction between oxalic acid and Potassium manganate (VII) vary with temperature? (1 mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
PROCEDURE II
Fill a burette with solution A. Pipette 25cm3 of solution C into a conical flask and titrate the solution A against solution C until a permanent pink colour just appears. Record your results in table II below and repeat the procedure to fill the table.
|
I |
II |
III |
|
|
Final burette reading (cm3) |
|||
|
Initial burette reading (cm3) |
|||
|
Volume of solution A used (cm3) |
(4 marks)
Determine the average volume of A used ……………………………………….cm3
(Show how you arrive at your answer) (1 mark)
ii). Calculate the concentration of solution C in moles per litre (Fe, = 56, S = 32,
O = 16, N =1 4, H = 1) (2 marks)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Find the number of moles of solution C used. (1 mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
iv) Given the ionic equation for the reaction is
5Fe2+(aq) + MnO4-(aq) + 8H+(aq) 5Fe3+(aq) + Mn2+(aq) + 4H2O(l);
Find the number of moles of solution A used. (1 mark)
(v) Determine the concentration of the Potassium manganate (VII), solution A in moles per litre. (2 marks)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- You are provided with solid Q. Carry out the tests below and record your observations and inferences in the table below.
- Place half a Spatula full of solid Q in a clean dry test-tube and heat gently then Strongly.
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
ii). Place the remaining solid Q in a boiling tube and add about 5cm3 of distilled water and shake well. Divide the resulting mixture into four portions for the tests below.
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
a). To the first portion add Sodium hydroxide solution dropwise until in excess.
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
b). To the second portion add 2-3 drops of dilute Sulphuric (VI) acid
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
c). To the third portion add aqueous ammonia dropwise until in excess
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
d). To the fourth portion add 2-3 drops acidified barium nitrate solution
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
- You are provided with solid L. carry out the tests below on L and record the observations and inferences in the spaces provided.
- Place half of solid L in a boiling tube and add about 5cm3 of distilled water
(i)
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
Divide the solution into two portions and carry out the tests below.
(ii). To the first portion add 2-3 drops of acidified potassium manganate (VII).
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
(iii). To the second portion add Sodium carbonate provided (1 mark)
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
(b). Place the remaining solid L in metallic spatula and ignite it.
|
Observations |
Inferences |
|
(1 mark) |
(1 mark) |
MARKING SCHEME
- Table I/procedure I
- Complete table – (1mark)
5 values -1mk
3-4 values ½ mk
1-2 values 0 mk
Accuracy (1mk)
Compare the first value with teachers value I within range ±2 units award 1 mark otherwise award 0 mark if outside the range
Trend – (1mk)
Continuous decrease in time (1mk)
Graph (3mk)
Scale – ½ mk
Occupy at least 8 squares on both axes
Labelling axes – ½ mk
Both axes labelled correctly showing correct variables- ½ mk
(Units may or may not be given. But if given must be correct. Otherwise penalize fully for wrong units
Plotting 1 mk
4-5 correctly plotted points -1mk
2-3 correctly plotted points – ½ mk
Shape/curve-1mk
Smooth curve – 1mk - Correct showing on graph√1 1mk. Correct reading from graph – (1 mark)
- Rate of reaction increase with increase in temperature√ 1mk
- Complete table – (1mark)
Procedure II
Table
Complete Table (C.T- 1 mark
C.T with 3 titrations 1 mark
C.T with 2 titrations 1 mark
C.T with 1 0 mark
Penalties
- Inverted table penalize ½ mk
- Wrong arithmetic ½ mk
- Unrealistic values below 1cm3 and above 50cm3 penalize ½ mk
NB/ penalize to a maximum of ½ mk
Decimal place (D.P) (1mk)
- Values to 1 d.p or 2 d.p of 25, 50, 75 i.e
- 2nd d.p should be 0 or 5
Accuracy (A) – 1mk
- If any value is within the range ±0.1 of school value award 1 mk
- If any value is within the range of ±0.2 of school value award ½ mk
Principle of averaging (P.A) – 1mk
- Average value that are ±0.2 of each other (1mk)
Final answer/accuracy (F.A) – 1mk
- Compare the averaged value with school value.
- If within range of ±01 1mk, if range of ±0.2 ½ mk
(ii). RFM of (NH4)2SO4. FeSO4. 6H2O = 392
.∴concentration= 19.6/392√1
= 0.05moles√1 (2mks)
(iii). Moles of C used =
.(0.05 x 25)/1000 √1/2 = 0.00125 moles√1/2
(iv). Moles of A used = 1/5 x 0.00125√1/2
= 0.00025 moles √1/2
(v) Average tire → 0.00025 moles
1000cm3 →
.(0.00025 x 1000√1 )/(Average tutre )= correct answer √1
2.(i).
|
Observation |
Inference |
(Any 2 ( ½ x 2) (1mk |
(Any one for 1 mark) |
(iii).
|
Observation |
Inference |
|
|
(a).
|
Observation |
Inference |
|
White ppt 1/2 soluble in excess 1/2 |
Zn2+,Pb2+, Al3+ present 1 (3 ions 1 mk) (2 ions ½ mark 1 ion 0mk Correctly inferred
|
(b).
|
Observation |
Inference |
|
No white precipitate |
Zn2+, Al3+ present 1
|
(c)
|
Observation |
Inference |
|
White precipitate 1/2 soluble in excess 1/2 (1mk) |
Zn2+ 1Present (1mk)
|
(d).
|
Observation |
Inference |
|
White precipitate formed 1 (1mk) |
SO42- present 1 (1mk)
|
3.(a)
(i)
|
Observation |
Inference |
|
Solid dissolve 1/2 to form colourless solution 1/2 |
Polar substance 1
|
(ii).
|
Observation |
Inference |
|
Decolourize potassium manganite (VII) / potassium manganite (VIII) change from purple to colourless |
C = C/-C C present any for 1 mk |
(iii).
|
Observation |
Inference |
|
Effervescence/bubbles/fizzing (1mk) |
R-COOH/H+/H3O+ present (1mk) |
(b).
|
Observation |
Inference |
|
Burns with yellow/smoky/sooty/luminous flame (1mk) |
C = C / -C C- present (1mk) |
CONFIDENTIAL
- Apart from the laboratory fittings supply the following
- 100cm3 solution A - 0.02M Acidified potassium manganite (VII) (H+/KMnO4)
- 100cm3 Solution B - 0.05M Oxalic acid
- 100cm3 Solution C - containing 4.9g of (NH4)2SO4 FeSO4.6H2O in 250cm3 of solution)
- 50ml measuring cylinder
- 5 Test tubes
- 1 boiling tube
- 250ml glass beaker
- Thermometer
- Stopwatch
- Burette
- Pipette
- Two conical flasks
- About 1g of solid Q (ZnSO4)
- Distilled water
- About 0.5g of solid L (oxalic acid)
- Litmus papers
- Metallic spatula
- Means of Heating
- 1g sodium carbonate
Access to
- 1 M Sodium hydroxide solution
- 1M Ammonia solution
- 5M Barium Nitrate solution – Acidified
- 1M sulphuric (VI) acid
- Acidified potassium Manganate (VII)
NB
0.02M of H+/KMnO4 is prepared by dissolving 3.16g of KMnO4 in 400cm3 of 2M H2SO4. Add distilled water to make 1 litre of solution.
Download Chemistry Paper 3 Questions and Answers - Arise and Shine Pre Mock Exams 2023.
Tap Here to Download for 50/-
Get on WhatsApp for 50/-
Why download?
- ✔ To read offline at any time.
- ✔ To Print at your convenience
- ✔ Share Easily with Friends / Students