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MIGORI – NYATIKE DISTRICT CHEMISTRY PRACTICAL QUESTIONS
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 and F will be provided by the council. Solid E is highly deliquescent and
should be handled cautiously
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
(i) Using a ruler, make 6 marks at 2cm length interval on the Magnesium ribbon provided.
(ii) 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.
(iii) Record in table I below. Place another piece of magnesium ribbon (2cm) to the same
solution and again note the time taken.
(iv) Repeat the procedure until all six pieces of magnesium ribbon have reacted with
the same solution initially placed in the beaker
(v) Complete the table I below:
Note: Keep the solution obtained in this experiment for use in procedure II
(a) 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) |
(b) (i) Plot a graph of total length of magnesium ribbon added against reciprocal of time (1/t)
for the reaction to go to completion
(ii) From your graph, determine the time taken when 4.5cm length of magnesium ribbon
reacts completely. (Show parts on the graph)
(iii) Write a chemical equation for the reaction between magnesium and sulphuric acid
(iv) 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 mole of sulphuric acid that were
used up during the reaction
(v) From your graph, state and explain the relationship between the length of magnesium
ribbon and the reciprocal of time (1/t)
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
(f) Table II
Titration | I | II | III |
Final burette reading (cm3) | |||
Initial burette reading (cm3) | |||
Volume of solution B (cm3) used |
(c) (i) Determine the average volume of solution B used
(ii) Calculate the number of moles of sodium hydroxide solution B used
(d) Calculate:
(i) The number of moles of sulphuric acid in 25.0cm3 of solution D
(ii) The number of moles of sulphuric acid in 100cm3 of solution D
(e) Determine the total number of moles of sulphuric acid in 50cm3
of solution A
(f) Calculate the concentration of the original sulphuric acid solution A in moles per litre
2. You are provided with solid E. Carry out the following tests and write your observations and
inferences in the table below:
(a) Place all the solid E in a boiling tube. Add about 15cm3 of distilled water and shake
vigorously for about 2 minutes
b) (i) divide the solution into five equal portions in five different clean test tubes.
(i) To the first portion, add 2M ammonia solution drop wise until in excess
ii) To the second portion add 2M Sodium hydroxide solution drop wise until in excess
iii) To the third portion add 4 drops of 2M Lead (II) nitrate solution
iv) To the fourth portion, add 4 drops of 0.2M silver nitrate solution, then add 2M ammonia
solution drop wise, until in excess
(v) 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:-
3. You are provided with solid F. Carry out the tests below. Write your observations and inferences
in the spaces provided
(a) Place about a half of solid F on a metallic spatula and burn it using a Bunsen burner flame
(b) Place the remaining of solid F in a boiling tube. Add about 10cm3of distilled water and
shake the mixture well.
(c) (i) Divide the mixture obtained into three portions.
(ii) To the first portion, add a small amount of solid sodium hydrogen carbonate
(iii) To the second portion, add about 1cm3 of acidified potassium dichromate (VI)
and warm
(iv) To the third portion, add two drops of acidified potassium magnate (VII)
MIGORI –NYATIKE DISRTICT CHEMISTRY PRACTICAL ANSWERS
1. (a)
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 (S–) t | 0.00667 | 0.00526 | 0.00444 | 0.0033 | 0.00233 | 0.002 |
CT – 2
D – 1
A – 1
T – 1
S = ½
P = 1
C = 1
(ii) 1 = 0.00510 √½ From the graph and must be shown. Showing. √½
t
t = 1 √½ = 196.5 seconds. √½
0.00510
(iii) Mg(s) + H2SO4(aq) MgSO4(s) + H2(g)
√½
1 : 1 With correct physical state.
(iv) Moles of Mg = 0.12
√½ = 0.005 moles √½
- 1mk
Moles of H2SO4 used = 0.005 moles (1 : 1)
(v) 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 |
Find burette reading (cm3) | 15.3 | 30.5 | 45.7 |
Initial burette reading | 0.0 | 15.3 | 30.5 |
Volume of solution B used (cm3) | 15.3 | 15.2 | 15.2 |
CT = 1
D = 1
AC = 1
PA = 1
TA = 1
5
(c) (i) 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
(ii) 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
(d) (i) Ans in c (ii)
√½ = C.A. √½ i.e. 0.007617 = 0.003809 moles
2 1 mk
(ii) Ans. in d (i) x 4 = C.A.
i.e o.003809 x 4 = 0.015236 moles. 1 mk
(e) 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
(f) Ans. in e x 1000 cm3 = C.A.
50 cm3
i.e. 0.020236 x 1000 = 0.40472 M
50
2. (a)Observations Inferences
Dissolves to form colourless solution . √½ Soluble salt or absence of coloured irons
i.e Fe3+, Fe2+, Cu2+
√½
1 mk
(b) (i) Observations Inferences
No white ppt. √½ Pb2+, Al3+ or Mg2+ absent
(½ mk) Or (½ mk)
NH+4, Na+, or K+ may be present. √½
(ii) Observations Inferences
No white ppt. √½ NH+4, Na+
√½ or K+ possibly present. √½
Or (1 mk)
(½ mk) Pb2+ Al3+, Zn2+ absent
1 ½ mks
(iii) Observations Inferences
White ppt. formed. √½ CO32-, SO42- Or Cl– present. √1
( ½ mk) (1 mk)
½ mks
(iv) Observations Inferences
White ppt. √ ½ dissolves in excess Cl-1 present. √1
ammonia √ ½ solution to form
colourless solution. (1 mk)
2 mks
(v) Observations Inferences
Golden yellow flame. √½ Na+ present. √1
(½ mk) (1 mk)
1 ½ mks
3. (a) Observations Inferences
Burns with yellow flame – Long chain hydrocarbon
sooty /smoky flame. √½ – Unsaturated organic compound. √½
Or
- Hydrocarbon with high C – H ratio
or
C = C or
C ≡ C
(b) Observations Inferences
Dissolves to form Polar organic compound/ soluble salt/ soluble comp. √1
colourless solution. √1
(1 mk) (1 mk)
2 mks
(c) (i) Observations Inferences
Effervescence /bubbles Presence of H+ / H3O+ – COOO. √½
/fizzing. √½
(½ mk) (½ mk)
1 mk
(ii) Observations Inferences
Orange colour remains Absence of R –OH. √½
the same / persists i.e
does not change green. √½
(½ mk) (½ mk)
1 mk
(iii) Observations Inferences
KMnO4 decolourized i.e
changes from C ═ C Or – C ≡ C −
purple to colourless√1 Or
Unsaturated organic compound. √1
(1 mk)