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MUMIAS DISTRICT CHEMISTRY PRACTICAL QUESTIONS
CONFIDENTIAL
INSTUCTIONS.
In addition to the apparatus and fittings found in the laboratory each candidate should have:
- One 25ml pipette
- One 3-way pipette filler
- One 0-50m/s Burrette
- Two 250m/s conical flask
- One 100ml measuring cylinder
- One 100ml glass beaker
- One thermometer (-10oC to 110oC)
- One stop watch / clock
- One label
- One 10m/s measuring cylinder
- White tile
- 250ml beaker
- Stand and clamp
- 10cm3 of solution A
- 80cm3 of solution B
- 160cm3 of solution C
- 200cm3 distilled water supplied in wash bottle
- 10cm3 Potassium manganate
- 250cm3 1.0M sulphuric acid
- 75cm3 of solution X
- About 0.5g of solid K
- About 0.5g of solid F
- One blue and one red litmus papers
- One metallic spatula
- Six dry and clean test-tubes
- One boiling tube
- About 0.5g Sodium hydrogen carbonate
ACCESS TO:
- Source of heat (Bunsen burner)
- Phenolphthalein indicator supplied with a dropper.
- Solution Q (aqueous sodium sulphate) supplied with a dropper
- Acidified lead II nitrate supplied with a dropper
- Ethanol
- Conc. H2SO4
NOTE:
- Solution A is 4.0m hcl
- Solution B is 0.1m H2C2O4.2H2O
- Solution C is 0.2m NaOH
- Solution X is made by dissolving 5g of sugar (sucrose) in 100m/s distilled water
- Potassium Manganate (VII) solution D is made by dissolving 3.16g of the solid in
600cm3 of distilled water and diluting to 1 litre.
- Solid K is Zinc chloride
- Solid F is oxalic acid
Question 1
You are provided with:
- Aqueous Hydrochloric acid solution A
- Solution B containing 6.3g of dibasic acid, H2C2O42H2O in 500cm3 of solution.
- Aqueous sodium hydroxide solution C
- Phenolphthalein indicator
You are required to:
(a) Standardize the sodium hydroxide solution C
(b) Use the standardized solution C to determine the concentration of solution A
Procedure 1
- Fill the burette with solution B
- Using a pipette and pipette filler, place 25.0cm3 of solution C into a 250ml conical flask.
- Add 2-3 drops of Phenolphthalein indicator
- Titrate solution B against solution C
- Repeat the procedure and complete table 1 below:
Table 1
I | II | III | |
Final burette readings (cm3) | |||
Initial burette readings (cm3) | |||
Volume of solution B used (cm3) |
(a) Calculate the average volume of solution B used
(b) Calculate the concentration of the dibasic acid ( C = 12, H = 1, O = 16)
(c) Calculate the molarity of solution C
Procedure 2
- Using a 100cm3 measuring cylinder, measure 90cm3 of distilled water and place
it into a 250cm3 beaker.
- Add 10cm3 of aqueous hydrochloric acid solution A
- Using a 10cm3 measuring cylinder, mix the solution well and label it solution D
- Fill a burette with solution D.
- Pipette 25.0cm3 of the solution C into a 250cm3 conical flask
- Titrate using phenolphthalein indicator
Record your results in table 2
Table 2
I | II | III | |
Final burette readings (cm3) | |||
Initial burette readings (cm3) | |||
Volume of solution D used (cm3) |
(a) Calculate the average volume of solution D used
(b) How many moles of hydrochloric acid were present in 100cm3 of solution D
(c) Calculate the molarity of the original solution A used
Question 2
You are provided with:
- 1.0M sulphuric acid
- Potassium manganate (VII) solution D
- Aqueous glucose, solution X
You are required to:
Determine the rate of reaction between acidified potassium manganate (VII) and aqueous
glucose at different temperatures.
Procedure
- Place 2cm3 of solution D into a 250ml beaker. Using a 100ml measuring cylinder,
add 50cm3 of 1.0M Sulphuric acid to the beaker containing solution D.
- Heat the mixture to about 65oC, add 15cm3 of solution X and start a stop watch immediately.
- Stir the mixture using a thermometer and note the time and temperature at which the
colour of the mixture changes from purple to colourless.
- Clean the beaker and repeat the procedure at temperatures, 60oC, 55oC, 50oC
and 45oC to complete table 3 below:-
Table 3
Temperature before mixing (oC) | 60 | 55 | 50 | 45 |
Temperature when solution becomes colourless (oC) | ||||
Time (seconds) | ||||
1/time (s-1) |
(a) Plot a graph of 1/t (y-axis) against the temperature at the point when the solution becomes
colourless
(b) From your graph, determine the time that the reaction would take if the temperature at
which the solution becomes colourless is 42.5oC
(c) Explain the shape of your graph
Question 3.
You are provided with:
- Solid K
Procedure
Carry out the tests below. Record your observations and inferences in the spaces provided.
(a) Heat about half spatula end full of solid K in a clean test tube, heat gently then strongly.
Test any gas produced using blue litmus papers.
(b) Dissolve the remaining solid K in a boiling tube in about 10cm3 of distilled water and
use the solution for the tests below:
(i) To about 2cm3 of solution K, add aqueous potassium hydroxide dropwise until in excess
(ii) To about 2cm3 of solution K, add about 5cm3 of solution Q (aqueous sulphate)
(iii) To about 3cm3 of the solution K, add about 6cm3 of acidified lead II nitrate
You are provided with:
- Solid F
Procedure
Add about 10cm3 of distilled water into half spatula end full of solid F in a boiling tube
and shake thoroughly.
(c)To about 2cm3 of solution F, add the whole of sodium hydrogen carbonate
(d) To about 2cm3 of solution F, add about 5 drops of acidified potassium manganate (VII) then
warm the mixture.
(e) Place about 5cm3 of ethanol in a test-tube and add drops of concentrated sulphuric acid then
add the remaining solid F. Warm the mixture carefully. Shake well and pour the mixture into
20cm3 of water in a beaker
MUMIAS DISTRICT CHEMISTRY PRACTICAL ANSWERS
TABLE 1,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, (5 mks)
Distributed as follows:
i) Complete table (1 mk)
Values must be 0.2 of each other.
ii) Use of decimal (1 mk)
Values should be in 1d.p or 2d.p consistently used
iii) Accuracy (1 mk)
Compare the school value to nay of the readings and award as follows
IF 0.1 award 1 mk
IF 0.2 award ½ mk
Outside 0.2 award 0 mk
iv) Principle of averaging (1 mk)
- Award 1 mk for consistent values averaged
- Penalize ½ mk for rounding off the answer to 1d.p unless it divides exactly
- Inconsistent values averaged – award 0 mk
v) Final answer 1mk
– Compare the averaged value to the school value
If 0.1 award 1 mk
If 0.2 award ½ mk
If outside award 0 mk
CALCULATIONS
a) Titre 1 + Titre II + Titre III = Answer
3
b) RFM of acid = 2 + 2 912) + 4(16) + 2(2 + 16)
= 126
If 500cm3 contains 6.3 g
1000cm3 contains ?
6.3 x 1000 = 12.6dm3
Concentration = 12.6g/dm3
Or 0.1 M
c) Molarity of solution C
Acid : Alkali
1 : 2
If 1000cm3 contains 0.1 moles
25cm3 contains ?
25×0.1 = 0.0025 moles
1000
From mole ratio: 25cm3 of alkali contains
0.0025 x 2 = 0.005 moles
If 25cm3 alkali contains 0.005 moles
100cm3 alkali contains 0.005×1000
25
= 0.2 moles
Molarity = 0.2 M
Procedure 2
TABLE 2
Marking should be done as in table 1
CALCULATION
a) Titre I + Titre II + Titre III = answer
3
b) 25cm3 of NaOH contains 0.005 moles
Mole ration 1 : 1
Moles of acid = 0.005 moles
If Titre in (a) of solution D contains 0.005 moles
1000cm3 of solution D contains:
0.005 x 1000 = answer in moles
Titre in a
c) 10cm3 of A contains moles in (b) above
1000cm3 of A contains
Ans in b x 100 = Answer
10
NB This answer should be close or equal to 4.0M
Question 2
TABLE 3 (5 mks)
Distributed as follows
i) Complete table (1mk)
– Award 1 mk for completely filled table (at least 8 values)
ii) Use of decimals (2 mks)
- Use of decimals for temperature readings award 1 mk
- Use of correct decimals for time readings award 1 mk
NB Penalize ½ mk if i/t is given as fraction
iii) Trends
Trend for temperature 1mk (i.e. should be decreasing)
Trend for time 1 mk(should be increasing)
GRAPH
Should be distributed as follows:
- Labelling the axes ½ mk for both axes
- Scale ½ mk (at least ¾ pg)
- Plotting I mk
- Shape (accept a curve and award 1 mk)
Question 3
Test for solid K
Observations | Inferences | |
a) | – colorless liquid condenses at the cooler parts of the test tube – Cracking sound produced | – Presence of hydrated substance – Contains water of crystallization |
b)i) | – White precipitate soluble in excess | – Al3+, Zn2+ or Pb2+ ions present 3 stated 1mk, 2 stated ½ mk |
ii) | No white precipitate formed |
|
iii) | White precipitate formed
Test for solid F | Presence of SO2-4 or CL- Award 1 mk for any 2 Award ½ mk for any 1 10n given |
c) | Effervescence or bubbles produced | Presence of H+, H3O+, R-COOH |
d) | Decolorises acidified KMnO4 or turns KMnO4 to colourless | Presence of reducing agent C = C – C = C- Or ROH, SO3 |
e) | Fruity or sweet smell | R- COOH confirmed |