Questions
Instruction to Candidates:
- Answer ALL the questions in the spaces provided after EACH question in the question-paper.
- You are NOT allowed to start working with the apparatus for the first 15minutes of the 2¼ hours allowed for this paper. This time is to enable you read the question-paper and make sure you have ALL the chemicals and apparatus that you may need.
- Mathematical tables and silent electronic calculator may be used.
- ALL working MUST be clearly shown where necessary.
QUESTION 1.
You are provided with:
- Sulphuric acid solution A
- 0.5M sodium hydroxide solution B
- Magnessium ribbon labelled C
You are required to:-
- Investigate the rate of reaction between solution A and metal C
- Determine the concentration of sulphuric acid in moles per litre
Procedure I
- Using a ruler, make 6 marks at 2cm length interval on the Magnesium ribbon provided. Cut the magnesium ribbon into 2 cm long pieces.
- Transfer 50cm3 of acid solution using a measuring cylinder into a clean dry 100ml beaker.
Place 2cm length piece of magnesium ribbon into the beaker with the acid and immediately
start the stop watch/clock. Shake gently and note the time taken for the piece of
magnesium ribbon to react completely. - Record in table I below. Place another piece of magnesium ribbon (2cm) to the same solution and again note the time taken.
- Repeat the procedure until all six pieces of magnesium ribbon have reacted with
the same solution initially placed in the beaker - Complete the table I below:
Note: Keep the solution obtained in this experiment for use in procedure II- Table I
Piece of magnesium added 1 2 3 4 5 6 Length of magnesium added (cm) 2 4 6 8 10 12 Time taken t(second) Reciprocal of time 1/t(s-1) -
- On the grid provided, plot a graph of total length of magnesium ribbon added against reciprocal of time (1/t) for the reaction to go to completion. (3 marks)
- From your graph, determine the time taken when 4.5cm length of magnesium ribbon to react completely. (1 mark)
- Write a chemical equation for the reaction between magnesium and sulphuric acid. (1 mark)
- Given that the mass of solid V, which reacted was 0.12g and that atomic mass of magnesium is 24.0g, determine the number of moles of sulphuric (VI) acid that were used up during the reaction. (1 mark)
- From your graph, state and explain the relationship between the length of magnesium ribbon and the reciprocal of time (1/t) (1 mark)
- Table I
Procedure II
Place all the solution obtained in procedure I in a clean 100ml measuring cylinder.
Add distilled water to make 100cm3 of solution. Transfer all the solution into a beaker
and shake well. Label it solution D. Fill the burette with solution B. Pipette 25.0cm3
of solution D into a conical flask. Add 2-3drops of phenolphthalein indicator and titrate
with solution. Record your results in the table II below. Repeat the titration two more times
Table II
Titration | I | II | III |
Final burette reading (cm3) | |||
Initial burette reading (cm3) | |||
Volume of solution B (cm3) used |
(4 marks)
-
- Determine the average volume of solution B used . (1 mark)
- Calculate the number of moles of sodium hydroxide solution B used. (1 mark)
- Calculate:
- The number of moles of sulphuric acid in 25.0cm3 of solution D. (1 mark)
- The number of moles of sulphuric acid in 100cm3 of solution D. (1 mark)
- Determine the total number of moles of sulphuric acid in 50cm3 of solution A. (1 mark)
- Calculate the concentration of the original sulphuric acid solution A in moles per litre. (1 mark)
QUESTION 2.
You are provided with solid E. Carry out the following tests and write your observations and
inferences in the table below:
- Place all the solid E in a boiling tube. Add about 15cm3 of distilled water and shake vigorously for about 2 minutes.
Observation Inferences - Divide the solution into five equal portions in five different clean test tubes.
- To the first portion, add 2M ammonia solution drop wise until in excess.
Observation Inferences - To the second portion add 2M Sodium hydroxide solution drop wise until in excess.
Observation Inferences - To the third portion add 4 drops of 2M Lead (II) nitrate solution.
Observation Inferences - To the fourth portion, add 4 drops of 0.2M silver nitrate solution.
Observation Inferences - Clean one end of the glass rod provided. Dip the clean end of the glass rod in the fifth portion. Remove the end and heat it in the non-luminous part of a Bunsen burner flame. Note the colour of the flame and record below.
Observation Inferences
- To the first portion, add 2M ammonia solution drop wise until in excess.
QUESTION 3.
You are provided with solid F. Carry out the tests below. Write your observations and inferences
in the spaces provided
- Place about a half of solid F on a metallic spatula and burn it using a Bunsen burner flame.
Observation Inferences - Place the remaining of solid F in a boiling tube. Add about 10cm3 of distilled water and shake the mixture well.
Observation Inferences - Divide the mixture obtained into three portions.
- To the first portion, add a small amount of solid sodium hydrogen carbonate.
Observation Inferences - To the second portion, add about 1cm3 of acidified potassium dichromate (VI) and warm.
Observation Inferences - To the third portion, add two drops of acidified potassium magnate (VII)
Observation Inferences
- To the first portion, add a small amount of solid sodium hydrogen carbonate.
Confidential
INSTRUCTIONS.
Apart from the normal fittings in the laboratory, each candidate will need the following chemicals and apparatus.
- 500ml of distilled water supplied in a wash bottle
- 50ml burette
- 25ml
- a pipette filler
- 2 conical flasks (250ml)
- Source of heat (means of heating)
- Stop watch/clock
- A ruler
- 100ml measuring cylinder
- 50ml measuring cylinder
- Complete retort stand
- 12cm long magnesium ribbon labelled C
- 100ml of solution A (sulphuric acid)
- 80ml of solution B (Sodium hydroxide soltn.)
- 100ml empty beaker
- Funnel
- Sand paper
- 3g of solid E
- 1g of solid F
- Means of labeling
- Six clean test tubes in a test tube rack
- 3 boiling tubes in a rack
- Metallic spatula
- About 0.2g of sodium hydrogen carbonate
- Glass rod.
Access
- 2M Ammonia solution supplied with a dropper
- 2M Sodium hydroxide solution supplied with a dropper
- 2M Lead (II) Nitrate supplied with a dropper
- 0.2M Silver Nitrate solution supplied with a dropper
- Acidified potassium dichromate (VI) supplied with a dropper
- Acidified Potassium Manganate (VII) supplied with dropper
N/B
- Solution A is prepared by accurately measuring 27.5cm3 of concentrated
- Sulphuric acid, then adding it to 700ml of distilled water then topping it to one litre. Density of acid 1.84g/cm3
- Solution B is prepared by accurately measuring 20g of NaOH pellets and dissolving it in 800cm3 of distilled water then topping to one litre with distilled water.
- Solid E – sodium chloride
- Solid F – maleic acid
Marking Scheme
-
- Table 1
Piece of magnesium added 1 2 3 4 5 6 Length of magnesium added (cm) 2 4 6 8 10 12 Time taken t(second) 150 190 225 295 430 500 Reciprocal of time 1/t(s-1) 0.00667 0.00526 0.00444 0.0033 0.00233 0.002
Complete Table – 1
Decimal point – 1
Accuracy – 1
Trend – 1 - Graph:
Straight line graph of best fit
Label of axis = ½
Scale = ½
Plotting = 1
Line = 1- 1 = 0.00510 √½ From the graph and must be shown. Showing. √½
t
t = 1 √½ = 196.5 seconds. √½
0.00510 - Mg(s) + H2SO4(aq) → MgSO4(s) + H2(g) √½
1 : 1 With correct physical state. - Moles of Mg = 0.12/24 √½ = 0.005 moles √½ 1mk
Moles of H2SO4 used = 0.005 moles (1 : 1) - Increase in length of M of ribbon results in decrease in (1/t )√½
This is done to gradual decrease in the concentration of the acid. √½
Table II
Titration I II III Final burette reading (cm3) 15.3 30.5 45.7 Initial burette reading (cm3) 0.0 15.3 30.5 Volume of solution B (cm3) used 15.3 15.2 15.2
- 1 = 0.00510 √½ From the graph and must be shown. Showing. √½
-
- T1 + T2 + T3 √½ = C.A √½ 1 fall are consistent
3
OR
i.e 15..3 + 15.2 + 15.2 √½ = 15.233 cm3 √½
3 - Moles of sodium hydroxide = 15.233 x 0.5 = 0.007617
1000
i.e. Ans in c (i) x 0.5 √½ = C.A. √½
1000 1 mk
- T1 + T2 + T3 √½ = C.A √½ 1 fall are consistent
-
- Ans in c (ii) √½ = C.A. √½ i.e. 0.007617 = 0.003809 moles
2 1 mk - Ans. in d (i) x 4 = C.A.
i.e o.003809 x 4 = 0.015236 moles. 1 mk
- Ans in c (ii) √½ = C.A. √½ i.e. 0.007617 = 0.003809 moles
- Ans in b (iv) + Ans. d(ii) √½ = C.A
0.005 + Ans. d (ii) = C.A
i.e. 0.005 + 0.015235 = 0.020236 moles. 1 mk - Ans. in e x 1000 cm3 = C.A.
50 cm3
i.e. 0.020236 x 1000 = 0.40472 M
50
- Table 1
2 | ||||
a | Observations | Inferences | ||
Dissolves to form colourless solution | Soluble salt or absence of coloured irons i.e Fe3+, Fe2+, Cu2+ |
|||
b | i | Observations | Inferences | |
No white ppt. | Pb2+, Al3+ or Mg2+ absent NH+4, Na+, or K+ may be present. √½ |
|||
ii | Observations | Inferences | ||
No white ppt. | NH+4, Na+ √½ or K+ possibly present. √½ Or (1 mk) Pb2+ Al3+, Zn2+ absent |
|||
iii | Observations | Inferences | ||
White ppt. formed. | CO32-, SO42- Or Cl- present. | |||
iv | Observations | Inferences | ||
White ppt. √ ½ dissolves in excess ammonia √ ½ solution to form colourless solution. (1mk) |
Cl-1 present. √1 | |||
v | Observations | Inferences | ||
Golden yellow flame. | Na+ present. | |||
3 | ||||
a | Observations | Inferences | ||
Burns with yellow flame sooty /smoky flame. √½ |
- Long chain hydrocarbon - Unsaturated organic compound. √½ organic compound with high C – H ratio |
|||
b | Observations | Inferences | ||
Dissolves to form colourless solution. √1 |
Polar organic compound/ soluble salt/ soluble compound √1 | |||
c | i | Observations | Inferences | |
Effervescence /bubbles /fizzing. √½ | Presence of H+ / H3O+ , R- COOH. √½ | |||
ii | Observations | Inferences | ||
Orange colour remains the same / persists i.e does not change green. √½ |
Absence of R –OH. √½ | |||
iii | Observations | Inferences | ||
KMnO4 decolourized i.e changes from C ═ C Or - C ≡ C − purple to colourless√1 Or |
Unsaturated organic compound. √1 |
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