MUMIAS DISTRICT CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

MUMIAS DISTRICT CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL

INSTUCTIONS.  

In addition to the apparatus and fittings found in the laboratory each candidate should have:

1. One 25ml pipette
   
2. One 3-way pipette filler
   
3. One 0-50m/s Burrette
   
4. Two 250m/s conical flask
   
5. One 100ml measuring cylinder
   
6. One 100ml glass beaker
   
7. One thermometer (-10^oC to 110^oC)
   
8. One stop watch / clock
   
9. One label
   
10. One 10m/s measuring cylinder
    
11. White tile
    
12. 250ml beaker
    
13. Stand and clamp
    
14. 10cm³ of solution A
    
15. 80cm³ of solution B
    
16. 160cm³ of solution C
    
17. 200cm³ distilled water supplied in wash bottle
    
18. 10cm³ Potassium manganate
    
19. 250cm³ 1.0M sulphuric acid
    
20. 75cm³ of solution X
    
21. About 0.5g of solid K
    
22. About 0.5g of solid F
    
23. One blue and one red litmus papers
    
24. One metallic spatula
    
25. Six dry and clean test-tubes
    
26. One boiling tube
    
27. About 0.5g Sodium hydrogen carbonate
    

ACCESS TO:

1. Source of heat (Bunsen burner)
   
2. Phenolphthalein indicator supplied with a dropper.
   
3. Solution Q (aqueous sodium sulphate) supplied with a dropper
   
4. Acidified lead II nitrate supplied with a dropper
   
5. Ethanol
   
6. Conc. H₂SO₄  
   

NOTE:

1. Solution A is 4.0m hcl
   
2. Solution B is 0.1m H₂C₂O₄.2H₂O
   
3. Solution C is 0.2m NaOH
   
4. Solution X is made by dissolving 5g of sugar (sucrose) in 100m/s distilled water
   
5. Potassium Manganate (VII) solution D is made by dissolving 3.16g of the solid in
   

600cm³ of distilled water and diluting to 1 litre.

1. Solid K is Zinc chloride
   
2. 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

 (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

 (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 65^oC, 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, 60^oC, 55^oC, 50^oC

and 45^oC to complete table 3 below:-  

Table 3

 (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 42.5^oC

 (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