MIGORI – NYATIKE DISTRICT CHEMISTRY PRACTICAL QUESTIONS and Answers

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.  

1. 500ml of distilled water supplied in a wash bottle
   
2. 50ml burette
   
3. 25ml
   
4. a pipette filler
   
5. 2 conical flasks (250ml)
   
6. Source of heat (means of heating)
   
7. Stop watch/clock
   
8. A ruler
   
9. 100ml measuring cylinder
   
10. 50ml measuring cylinder
    
11. Complete retort stand
    
12. 12cm long magnesium ribbon labelled C
    
13. 100ml of solution A (sulphuric acid)
    
14. 80ml of solution B (Sodium hydroxide soltn.)
    
15. 100ml empty beaker
    
16. Funnel
    
17. Sand paper
    
18. 3g of solid E
    
19. 1g of solid F
    
20. Means of labeling
    
21. Six clean test tubes in a test tube rack
    
22. 3 boiling tubes in a rack
    
23. Metallic spatula
    
24. About 0.2g of sodium hydrogen carbonate
    
25. Glass rod.
    

Access

1. 2M Ammonia solution supplied with a dropper
   
2. 2M Sodium hydroxide solution supplied with a dropper
   
3. 2M Lead (II) Nitrate supplied with a dropper
   
4. 0.2M Silver Nitrate solution supplied with a dropper
   
5. Acidified potassium dichromate (VI) supplied with a dropper
   
6. Acidified Potassium Manganate (VII) supplied with dropper
   

N/B

1. 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

1. 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.  

1. 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

(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

(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

 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) + H₂SO_4(aq) MgSO_4(s) + H_2(g)
√½

1 : 1 With correct physical state.

  (iv) Moles of Mg = 0.12
√½ = 0.005 moles √½

1. 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

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 CO₃^2-, SO₄^2- 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)