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NYAMIRA DISTRICT CHEMISTRY PRACTICAL QUESTIONS
CONFIDENTIAL
INSTRUCTIONS
Each candidate should be provided with:
- About 1g of malleic acid – solid P
- A clean metallic spatula
- Bunsen burner
- 500ml distilled water in a wash bottle
- Six test-tubes in a rack
- One test tube holder
- 2 boiling tubes
- About 1g of AlCl3 – solid M
- One blue and one red litmus paper
- One volumetric flask (250ml)
- One pipette 25cm3
- One pipette filter
- One label
- Solid G – oxalic acid (exactly 3g) in a stoppered container
- 50ml or 100ml measuring cylinder
- 100cm3 beaker
- One thermometer
- One stopwatch/clock
- About 0.2g NaHCO3 solid
- 100ml of solution H
- One burette (50ml)
- 2 conical flasks
Access to:-
- 0.2M Pb(NO3) Solution supplied with a dropper
- 0.2M Ba(NO3)2 Solution supplied with a dropper
- 0.1M KI Solution supplied with a dropper
- 2M NaOH Solution supplied with a dropper
- 2M NH3(aq) Solution supplied with a dropper
- Acidified K2CV2O7 Solution supplied with a dropper
Preparation instruction
– Dissolve 6.4g of KMnO4 in 400cm3 2M H2SO4 and top to 1litre using distilled water
1. You are provided with:
- 0.0238 Moles (equivalent to 3g) of solid G
- Solution H, 0.04M acidified potassium manganate (VII)
You are required to:
I. Determine the enthalpy of solution of solid G
II. The number of moles of water of crystallization in solid G
Procedure I:-
Using a measuring cylinder place 50cm3 of distilled water into a 100cm3 of beaker.
Stir the water gently with a thermometer and take its temperature after every half-minute.
Record the reading in table I below. At exactly two minutes, add all solid G to the water
at once. Stir well and take the temperature of the mixture after every half minute up to
the fourth minute. Record your results in table I. Keep the solutions for procedure II below:
Table I
(a)
Time (min) | 0 | ½ | 1 | 1 ½ | 2 | 2 ½ | 3 | 3 ½ | 4 |
Temperature (oC ) | X |
(b) On the grid provided, plot a graph of time (x-axis) against temperature
(c) (i) On the graph, show the change in temperature T
(ii) Calculate :
The molar enthalpy of solution (H solution)
(Assume density of solution = 1g/cm3 and show the sign of H solution specific heat
capacity of solution = 4.2jg-1k-1)
Procedure II
Transfer the contents of the beaker into a 250ml volumetric flask. Rinse both the beaker
and the thermometer with distilled water and add to the volumetric flask. Add more distilled
water to eh mark.
Label this solution G
Fill the burette with solution H
Using a pipette and pipette filter, place 25.0cm3 of solution G into a conical flask. Warm the
mixture to about 60oC. Titrate the hot solution G with solution H until a permanent pink colour
persists (while shaking). Record your readings in table 2. Repeat the titration two more times
and complete table 2
Table 2.
Titre | I | II | III |
Final burette reading | |||
Initial burette reading | |||
Volume of solution H used (cm3) |
(e) Calculate the:
1. Average volume of H used
II. Number of moles of potassium manganate VII used
III. Number of moles of G in 25cm3 solution G given that 2moles of potassium manganate
(VII) reacted completely with 5moles of G
IV. Relative formula mass of G
(f) Formula of G has the form G. XH2 Determine the value of X in the formula given
the relative formula mass for G is 90.0 and atomic mass of Oxygen is16 and that
of Hydrogen is 1.0
2. You are provided with solid M and carry out the tests below write your observations and
inferences in the spaces
(i) To a dry boiling tube, place all solid M and add 12cm3 of distilled water and use the
solution for the tests below:-
(ii) To 2cm3 of solution, add both litmus papers
(iii) To 2cm3 of solution, add aqueous sodium hydroxide drop wise until excess
(iv) To 2cm3 of solution, add aqueous ammonia drop wise until in excess
(v) To 2cm3 of the solution, add 2 drops of aqueous potassium iodide
(vi) To 2cm3 of solution, add 3 drops of aqueous lead (ii)nitrate
(vii) To 2cm3 of solution, add 3 drops of aqueous Barium nitrate solution
2. B. You are provided with solid P. Carry out the test below. Write your observations and
inferences in the spaces provided:-
(a) Place one third of solid P on a metallic spatula and burn it using a Bunsen burner
(b) Place the remaining of solid P in a test-tube . Add about 6cm3 of distilled water and shake
the mixture (retain the mixture for use in test (c)
(c) (i) To 2cm3 of the mixture in (b) above add a spatula end full of NaHCO3 solid
(ii) To 2cm3 of the mixture, add 2cm3 of acidified potassium dichromate (VI) and warm
(iii) To 2cm3 of the mixture add two drops of acidified potassium manganese (VII) and shake well
NYAMIRA DISTRICT CHEMISTRY PRACTICAL ANSWERS
1. (a)
Time (min) | 0 | ½ | 1 | 1 ½ | 2 | 2 ½ | 3 | 3 ½ | 4 |
Temperature (oC ) | 19.0 | 19.0 | 19.0 | 19.0 | X | 16.0 | 15.0 | 15.0 | 15.0 |
Complete – 1mk
- 8 readings – 1mk- penalize – ½ of space not filled
- ½ for unrealistic values T 100 or 40
- ½ all constant t = 0 to t = 4
- ½ if T( T(2 ½ )
Decimal place – 1mk
– Accept whole number or to 1d.p of 0.5 or 0.0
Accuracy – 1mk S.V 2units
Trend – 1mk
Award ½ – where t = 0 – t – 1 ½ min = all constant
t = ½ – t ½ min – constant
Award ½ – t – 2 ½ to 4min –show a drop
(b) Graph
Ans – ½ – both axis correctly labelled
Scale = ½ – use more than ¾ big squares in both axis
Plotting -1
Labeling -1
3 mks
Penalize ½ inverted and scale to accommodate all plots
Plotting – all 8 points award 1mk
– 6pts & 7 award
– 5 award 0mk
Labelling – Award ½ for two straight lines.
– ½ for extrapolation
(b) (i) T = correct reading
(ii) Heat of solution = MCT
= 50g x 4.2Jg-1K-1 x 4.5K
= -50 x 4.2 x 45J
= –50 x 4.2 x 4.5 KJ
1000
Hsoln = ?
0.0238moles = -50 x 4.2 x4JKJ
1000
1mole= ?
= -50 x 4.2 x 4.5 KJ/mol–
1000 x 0.0238
= -Ans
Penalized if H – sign is + and not –ve (total 3mks)
TABLE 2
Titre | I | II | III |
Final burette reading | 24.4 | 24.5 | 24.3 |
Initial burette reading | 0.0 | 0.0 | 0.0 |
Volume of solution H used (cm3) | 24.4 | 24.5 | 24.3 |
Conditions:- A complete table …
3 consistent titrations 1ms
2 titrations done and are consistent…1mk
3 inconsistent titrations done and averaged 0mk
only 1 titration done…………….0mk
Penalty:
(i) Penalize ½mk for inverted table.
(ii) Penalize ½mk to unrealistic titre values e.g. volume cm3 unless explained.
(iii) Penalize ½mk for wrong arithmetic.
B- Use of decimals ….1mk
(Tied to 1st and 2nd rows)
Conditions
- Accept 1 decimal place / point if used consistently.
- Accept 2 decimal points , however the 2nd decimal point must be either 0.0 or 5.
Penalty
- Penalize fully if decimals are not used consistently
(C) Accuracy ….1mk
(i) Conditions (i) If any of the volume used is within 0.1cm3 of the school value (S.V)…
(ii) If there is one value within 0.2cm3 of the school value (S.V)… ( ½mk)
(D) Principles of averaging…..1mk
Conditions
- If 3 titrations done are consistent and averaged….
- If 3 titrations done and 2 are consistent and averaged ….1mk
- If 2 titrations done and are consistent and averaged….1mk
- If titration done …1mk
- If 3 titrations done and are inconsistent and averaged ….0mk
- If 2 consistent titrations averaged…0mk
- If 3titrations are done and are consistent but are averaged …..0mk
(E) Final answer …..1mk
Conditions
- If the answer of the titre value is within 0.1cm3 of the school value (S.V) award….1mk
- If the answer of the titre value is within 0.2cm3 of the school value …. ½mk
- If the answer is not within 0.2cm3of the school value (S.V) award….0mk
(e) Average volume of solution H used
24.5 + 24.4 + 24.3 = 24.4
3
II. 24.4 x 0.04 = 0.000976
1000
III. 5/2 x 0.000976 = 0.00244 (penalize ½ for wrong units)
IV. 3
250 x 0.00244
25
= 3 = 122.95
0.0244
= 123(no units) penalize for units
(f) 123-90 = 33
16 + (2×1) = 18x = 33
x = 33/18 = 1.833
x = 2
2. (a) (i)
(ii)
Observation | Inference |
– Blue litmus turns red. – No effect on litmus paper. | – Presence of H+/H3O in the solution. – Solution is acid (1 mk) |
Observation | Inference |
– White ppt. soluble in excess. (1 mk) | – Pb2+, Zn2+, Pb3+ present. (1 mk) |
(iii)
(iv)
Observation | Inference |
– White ppt. persisted insoluble in excess | – Al3+ or Pb2+ probably present |
(v)
Observation | Inference |
– Mixture remains colourless/ No yellow ppt. seen. (1 mk) | – Pb2+ absent (1glim). – Al3+ present |
(vi)
Observation | Inference |
– White ppt. seen. (1 mk) | – SO42-, CO32-, SO32- absent – Cl- is present (probably present) |
(B(b)
Observation | Inference |
– Solid melts forming a colourless and ignites /burns with Smoky / sooty flame. (1 mk) | – Low compound organic compound/presence of or –C C (accept absence of saturated organic compound). (1 mk) |
Observation | Inference |
– Dissolves in water forming colourless solution | – Solution compound /polar compound |
(c) (i)
Observation | Inference |
– Effervescence/ fizzling/bubbles of a colourless gas. – No effect on litmus paper. | Presence of – COOH/ H+/H3O+ ions. Solution is acid . (1 mk) |
(ii)
Observation | Inference |
– The solution remained orange. | – Absence of R-OH. (1 mk) |
(iii)
Observation | Inference |
Solution turns from purple to colourless solution is decolourised (1 mk) | – Presence of of –C C- |