BUTERE DISTRICT CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

BUTERE DISTRICT CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL

INSTRUCTIONS

Each student should be provided with:

1. 100 cm³ of solution M₂
   
2. 80 cm³ of solution M₁
   
3. 50 cm³ of solution M₃
   
4. Pipette (25 ml)
   
5. Burette (50 mls)
   
6. Methyl Orange indicator with a dropper
   
7. Two conical flasks
   
8. Filter funnel
   
9. Measuring cylinder (10 mls)
   
10. Measuring cylinder (50 mls)
    
11. Thermometer (-10 to 110⁰c)
    
12. 100 mls plastic beaker
    
13. 3 test tubes in a test tube rack
    
14. 1 Boiling tube
    
15. Solid W. (One spatula full)
    

Access to:

1. 2M NaOH(_aq) with a dropper
   
2. 2M NH₃ (_aq) with a dropper
   
3. 1M BaCl₂ with a dropper
   
4. 2M HNO₃ with a dropper
   
5. Distilled water in a wash bottle
   

Note:

1. Solution M₁ is prepared by mixing 53g of Sodium Carbonate and 42g of Sodium Chloride solid and dissolved to make one litre solution.
   
2. M₂ is 1M Hydrochloric acid.
   
3. M₃ is 1M Sodium Hydroxide.
   
4. Solid W is Aluminium Nitrate
   

1. You are provided with the following solutions:-

 – M₁ containing 95g of a mixture of sodium carbonate and sodium chloride per litre of solution.

 – M₂ which is 1M HCL.

 You are to determine the percentage of sodium chloride in the mixture.

Proceed as follows:

Pipette 25 cm³ of M₁ and titrate with M₂ from burette using 3 – 4 drops of methyl orange

indicator. Stop titrating when a permanent pink colour appears. Repeat the experiment and

complete the table below.

TABLE 1

 a) Determine the average volume of M₂ used. Show your workings.

 b) Determine the number of moles of M₂ used.

 c) Write down an ionic equation for the substances that react.

 d) Determine the number of moles of the base used.

 e) Calculate the concentration of sodium carbonate.

 f) Determine the mass of sodium carbonate in 1 litre of the solution.

(Na = 23, C = 12, O = 16)

g) Determine the percentage of sodium chloride in the mixture.

2. You are provided with the following solutions:-

 – 1 M HCl solution M₂

 – 1 M NaOH solution M₃

 You are expected to determine the molar heat of neutralization of hydrochloric acid.

Proceed as follows:

Measure 23 cm³ of M₂ and put in a 100 ml beaker. Measure its temperature and record in the

table below under first column. By use of a measuring cylinder measure 5 cm³ of M₃ and to M₂ in

the beaker. Stir with the thermometer and record the final steady temperature. Continue adding

5 cm³ at a time and recording the temperature till 35 cm³ has been added, complete the table

below.

a) TABLE II

b) Plot a graph of temperature (vertical axis) against volume of NaOH added.

c) From your graph determine:-

(i) Volume of 1M NaOH needed to neutralize 23 cm³ of 1M HCl

(ii) Rise in temperature ∆T.

 d) Calculate the amount of heat evolved in the above reaction. Take specific heat capacity of

solution to be 4.2. J/g/k, density of solution. 1g/cm³.

e) Calculate the number of moles of HCl used.

f) Hence determine the Molar heat of neutralization of hydrochloric acid.

3. You are given solid W. Carry out the tests below and answer accordingly.

 a) Take a spatula endful of W and put in a boiling tube. Add about 8cm³ of water and shake.

Keep the mixture for the tests below.

b) To about 2 cm³ of solution of W add sodium hydroxide (2M NaOH) drop wise till in excess.

c) To about 2 cm³ of solution W, add Ammonia solution (2M NH_2aq) drop wise till in excess.

d) To about 2 cm³ of solution W, add about 5 drops of Nitric acid (HNO_{3 (aq)}) followed by 2 drops

of Barium chloride.

BUTERE DISTRICT CHEMISTRY PRACTICAL ANSWERS

 TABLE 1

1. Complete table

Penalties

• Unrealistic burette reading.
  

• Arithmetic error
  
• Inverted table.
  

N/B Penalize ½ mk each to a max. of ½ mk

2. Use of decimal.

 – Consistent 1 d.pt. or 2 d.pt. –

 – If 2 d.pt. the last digit must be zero or five.

 – Otherwise award 0

 – Accept the consistency of zero.

3. Accuracy

 – Tied to the school value.

 – Check any of the titre readings.

(i) If any of them is within + 0.1 from S.V. award

(ii)If within + 0.2 unit award – (½ mk).

(iii) If outside + 0.2 unit award zero.

4. Principle of Averaging.

 (i) 3 consistent values average –

 (ii) 2 consistent values averaged – (½ mk)

 (iii) Otherwise award 0.

Penalties

 (i) Answer should be at least 2 d.p. unless divided exactly.

 b) No. of moles M₂ = ans(a) x 1
1

1000

Correct ans. 1

 c) 2H⁺ (aq) + CO₃^2-(aq) H₂O(l) + CO₂(g)

1. Balancing = ½ mk
   
2. States (correct) = ½ mk
   

1. Moles of base = ½ x ans. (b) 1 mk
   

= correct answer 1 mk

1. Concentration = answer in (d) x 1000
   1 mk
   

   25
   

= Correct answer 1 mk

f) Mass of Na₂CO₃ = 106 x ans. (e) 1 mk

= Correct answer 1 mk

 g) Mass of NaCl = 95 – ans. (f) (½)

% of NaCl = 95 – ans. (f) x 100

95

= Correct answer ½

2. a) TABLE 2

(i) Complete table 1 mk

(ii) Accuracy to S.V. 1 mk

(iii) Decimal 1 mk

(iv) Trend. 1 mk

 b) Graph

 c) (i) – Shown in graph (½ mk)

– Correct reading (½ mk)

(ii) ∆T shown in graph – (½ mk )

Correct answer from graph – (½ mk)

 d) ∆H = MC∆T = (23 + c(i) x 4.2 x c (ii) 1 mk

 Correct answer

 e) Moles = 1 x 23
½ = 0.023 moles  ½

1000

 f) Molar heat = 1 x ans. (d) 1

ans. (e)

= Correct answer. 1

CALCULATIONS

b. (i) Moles of soltn P = average titre x 0.2 ½ mk

1000

= correct Ans. ½mk

b. (ii) NaOH_(aq) + HCL_(aq) Nacl _(aq) + H2O _(l)

Mole ratio= NaOH: HCl is 1:1

Moles of NaOH soln S = 1 x Ans. b(i) ½mk

1

= corr. Ans.

b. (iii) 25cm³ soltn. S = Moles in Ans. b(ii)

100cm³ soltn. S = ?

= 100 x Ans. b(ii) ½mk

25

=Correct Ans. ½mk

(c) 100cm³ soltn S Moles in Ans. b(iii)

200cm³ Soltn S 200 x moles in Ans. b(iii) ½mk

100

moles in 25cm³ NaOH = 200 x moles in Ans. b.(iii) ½mk

100

= 2 x moles n Ans. b(iii)

= Correct Ans. ½mk

(f) Moles of R in 25cm³ = Ans. (e)

Moles of R in 1000 = ?

= 1000 x Ans (e) ½mk

25

= corr. Ans. ½mk

(g) (i) Molar mass of H₂SO₄ = 49 x 1

Moles in (f)

= Corr. Ans.

(g) (ii) Let R.A.M of A be equal to a

 2 + a = Ans. g(i)

a = Ans. g(i) – 2

= Corr. Ans.

2. (a) Table III…………………………………….. .

– Distributed as follows:-

Complete table …………………

– All columns filled 1mk

– Any 4 correctly filled ½mk

– Otherwise penalize fully

Accuracy……………..

Compare candidate’s initial temperature with S.V; if with  0.2 units award 1mk,

otherwise penalize fully.

Trend……………………1mk

Award 1mk for, increase then constant

(b) Award 4mks distributed as follows

Correct labelling……………1mk

Correct plotting……………1mk

Curve/line…………………….1mk

Appropriate scale…………1mk

. 4mks

(c) (i) Award 1mk for correct reading

(ii) Highest temperature-initial temp = corr.ans.

(d) Heat change = MCT (½mk)

= corr Ans (½mk)

(e) No. Vol. from highest temp change

(f) Moles used = vol. in (e) x 10

1000

= Corr. Ans.

 Moles in (f) produce heat change (d)

I mole = ?

= 1 x Heat change in (d)

Moles in (f)

= Correct answer (½mk)

3. (a) Observations Inferences

– Dissolves ½mk to form a colourless – Absence of coloured ions e.g. Cu²⁺, Fe²⁺, Fe³⁺

Solution ½mk

i) To the first portion, add Nitric acid followed by Barium nitrate solution.

 Observations Inferences

ii) To the second portion, add Nitric acid, followed by lead(ii) Nitrate solution

 Observations Inferences

iii) To the third portion, add a few drops until in excess

 Observations Inferences

iv) To the fourth portion, add a few drops until in excess

 Observations Inferences