MATUNGU DISTRICT CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

MATUNGU DISTRICT CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL

INSTRUCTIONS.

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 250 m/s conical flask
   
5. One stop watch /clock
   
6. One 250ml glass beaker
   
7. One 100ml measuring cylinder
   
8. One 100ml glass beaker
   
9. One thermometer (-10 to 110^oC)
   
10. One label
    
11. One piece of white paper
    
12. One measuring cylinder (10mls)
    
13. Six dry clean test tube on test-tube tack
    
14. One boiling tube
    
15. One clean dry metallic spatula
    
16. 250cm³ distilled water in wash bottle
    
17. One filter paper (dry)
    
18. One filter funnel
    
19. One glass rod
    
20. About 0.5g sodium hydrogen carbonate supplied in a stoppered bottle
    
21. 0.5g of solid F (accurately measured)
    
22. About 130cm³ of sodium thiosulphate (0.25M sodium thiosulphate, solution D)
    
23. About 30cm³ of 2.0M HCl (solution E)
    
24. About 0.5g solid T
    
25. About 0.5g solid X
    
26. About 180cm³ of solution B
    
27. About 80cm³ of solution A
    

Access to:

1. Phenolphthalein indicator supplied with a dropper
   
2. Bunsen burner (source of heat)
   
3. Acidified potassium manganate (VII) solution
   
4. Concentrated sulpuric acid
   
5. Ethanol in a stoppered bottle
   

NOTE:

1. Solid X – Oxalic acid
   
2. Solid T – Calcium Chloride
   
3. Solution A – 0.5M NaOH
   
4. solution B – 0.5M HCl
   
5. Solid F – ZnCO₃ (Zinc carbonate)
   

Question 1.

You are provided with:

• Solution A, sodium hydroxide
• Solution F, 0.2g of a carbonate (MCO₃)
• Solution B, 0.5M Hydrochloric acid
• Phenolphthalein indicator

You are required to:

(a) Standardize solution A with solution B

Using a pipette and a pipette filler place 25.0cm³ of solution A into a 250ml conical flask

Add 2-3 drops of phenolphthalein indicator

 Record your results in table 1 below

 Repeat the procedure two more items and complete table 1

Table 1

(a) Calculate the average volume of solution B used

 (b) (i) Determine the moles of sodium hydroxide used

 (ii) Calculate the molarity of Sodium hydroxide

Procedure II

• Place all the 0.2g of solid F into a 250cm³ beaker.

• Measure 100cm³ of the 0.5M hydrochloric acid solution using 100cm³ measuring cylinder and add it to the solid in the beaker.
• Shake well until effervescence stops; label this solution C
• Pipette 25.0cm³ of solution C into a 250cm³ conical flask
• Add 2-3 drops of Phenolphthalein indicator
• Titrate solution C against solution A
• Repeat the procedure and complete table II below:

Table II

Calculate the:

(a) Average volume of solution A used

(b) Number of moles of hydrochloric acid that was in the 25cm³ of solution C used

(c) (i) Number of moles of the Carbonate in 0.2g

(ii) Relative formula of the carbonate solid F

QUESTION 2

You are provided with:

• Solution D, 0.25M Sodium thiosulphate

• Solution E, 2.0M Hydrochloric acid

You are required to:

Determine the effect of temperature on rate of reaction.

Procedure:

-Place 50cm³ of solution D in 100ml glass beaker provided and record its steady temperature.

– Mark a cross (x) on a piece of white paper and place the beaker containing the thiosulphate on it.

– Measure 5cm³ of solution E and add it to the beaker with the thiosulphate and swire

carefully not to pour the content.

– Start a stop watch immediately the last drop of acid is added

– Look through the solution and note the time taken for the mark to become invisible

– Repeat the procedure with the thiosulphate heated to 30^oC, 40^oC, 50^oC and 60^oC

Record your results in table III below:

Table III

(a) Use your results to plot a graph of ¹/_t against temperature

(b) From your graph, determine the time taken if the temperature of the solution is 318K

(c) Explain how the rate of reaction changes with increase in temperature

QUESTION 3

Procedure 1:

You are provided with solid T.

Place a spatula full of solid T in a clean boiling tube then add about 10cm³ of distilled water.

Shake the mixture for about 1 minute then filter. Divide the filtrate into 4 portions.

(a) To the first portion add about 2cm³ of sodium hydroxide (solution A)

 (b) To the second portion add about 2cm³ of 2.0M hydrochloric acid

(c) To the third portion, add a few drops of phenolphthalein indicator

(d) To the fourth portion dip a clean glass rod and place the soaked end of the glass rod

onto a non-luminous flame

Procedure 2:

You are provided with solid X. Carry out the tests below and record your observation and

inferences in the table below:

Place one spatula end full of solid X in a boiling tube and add about 10cm³ of distilled water.

Shake well and use for the tests below:

 (a) To the 2cm³ of solution in a test-tube, add one spatula end full of sodium hydrogen carbonate

 (b) To 2cm³ of solution, add three drops of acidified potassium manganate (VII) solution

(c) Place about 5cm³ of ethanol in a test tube and add drops of concentrated sulphuric acid

then add a spatula end full of solid X. warm the mixture carefully. Shake well and pour

the mixture into 20cm³ of water in a beaker

CONFIDENTIAL Requirements:-

1. Solution X₁, acidified potassium manganate (VII) solution. It is prepared by dissolving
   

3.16g of KMnO₄ in 400cm³ of 2M H₂SO₄. add distilled water to make it up to 1litre solution

1. Solution X₂, 0.1M Iron (II) Sulphate
   

–It is prepared by dissolving 20.8G of Iron (II) Sulphate in1litre of distilled water, add

a few drops of concentrated sulphuric (VI) acid, to avoid oxidation.

1. Solution X₃ contains 3.45g of sodium nitrite in 1 litre of solution
   
2. Solid M – Potassium nitrate
   
3. Solid Y – (Oxalic acid)
   

1. You have been provided with:

 (i) Solution X₁, acidified Potassium manganate (VII) solution

 (ii) Solution X₂, 0.1M FeSO₄

 (iii) Solution X₃, Sodium Nitrite

You are required to:

1. Standardize solution X₁, using X₂
2. Use experimental results to write ionic equation for the reaction between manganate

(VII) ions and nitrate ions

Procedure I:-

1. Fill the burette with solution X₁
2. Pipette 25cm³ of solution X₂ into 250ml conical flask
3. Titrate solution X₂ with solution X₁ until a pink colour just appear
4. Record your results in table 1:

TABLE 1

Calculations:

(a) Calculate the average volume of solution X₁ used

(b) Calculate the number of moles of Fe²⁺ in 25cm³ of solution X₂ used

(c) If the ratio MnO₄-: Fe²⁺ is 1:5, calculate the concentration of MnO₄ ions in moles per dm³

Procedure II:

1. Rinse the conical flask and refill the burette with solution X₁
2. Pipette 25cm³ of X₃ into a clean conical flask
3. Warm this solution to about 50^oC (Note: Be accurate with temperature)
4. Titrate the solution in (iii) above against solution X₁ from the burette to a pink colour
5. Record your results in table II.

Calculations:

1. Calculate the average volume of X₁ used
2. Calculate the number of moles of :

 (i) Sodium nitrite in one litre of solution (Na = 23, N = 14, O = 16)

 (ii) Nitrite ions in 25cm³ of solution X₃ used

 (iii) Moles of solution X₁ used

(c) (i) Work out the approximate ratio Mno₄-: NO^–₂

(ii) Write down the ionic equation for the reaction between acidified manganate

(VII) ions and nitrite ions

2. You are provided with solid M. You are required to:

 (i) Carry out test on solid M

 (ii) Record your observations and inferences accordingly.

Procedure:-

1. (i) Dissolve solid M in 15cm³ of distilled water. Divide the resulting solution into six portions.

Record your observations

 (ii) Add 3-4 drops of Lead nitrate to the first portion

(iii) Add 3-4 drops of Barium nitrate solution to the second portion

(iv) Add 3-4 drops of sodium hydroxide solution to the third portion

 (v) Dip a glass rod into the fourth portion. Heat the end of glass rod dipped into the solution

in a non-luminous flame

(vi) Add 4 drops of acidified manganate (VII) to the fifth portion and warm the mixture

Q3.

1. Solid Y-1spatulaful

2. Solid Z-1spatulaful

3. 6 test tubes

4. 1 red + 1blue litmus papers

5. Metallic spatula

6. pH paper

3. (a) You are provided with solid Y

You are required to:

1. Carry out the test described below on solid Y
2. Record your observations and inferences
3. Test for any gas (es) produced

Procedure-

1. Place a spatula of solid Y into a boiling
2. Add about 15cm³ of distilled water and shake well
3. Divide the resulting solution into five portions
4. Use a universal indicator paper to test portion one of the solution

 (v) Add a spatula of sodium carbonate to the second portion

(vi) Add three drops of Potassium manganate (VII) solution to the 3^rd portion

(vii) Add three drops of bromine water to the 4^th portion. Warm the mixture if necessary

(viii) Place 2cm³ of ethanol in a test-tube. Add 2 drops of concentrated Sulphuric (VI) acid

and then a spatula end full of solid Y. Shake well and warm the mixture carefully, pour

the warm mixture into 25cm³ of cold water in a beaker and note the smell

Matungu District CHEMISTRY PRACTICAL ANSWERS

Question 1.

Table 1

Distributed as follows:

(i) Complete table

 Values must be ±0.2 of each other

(ii) Decimal place

Values should be n 1d.p or 2d.p consistently used.

(iii) Accuracy

Compare the school value to any of the readings and award as follows:

If ±0.1 award 1mk

± 0.2 award ½mk

Outside 0.2 award 0mk

(iv) Principle of averaging

• Award 1mk for consistent value only.
  
• Penalize ½mk for rounding of the answer to 1d.p unless it divides exactly.
  
• In consistent values averaged award 0mk
  

(v) Final answer value to the school to compare the average value to the school value:-

If ±0.1 award 1mk

If ±0.2 award ½mk

If outside award 0mk

Calculations

(a) Titre 1 + Titre II + Titre III = Answer

3

(b) NaOH_(aq) + HCl_(aq) NaCl_(aq) + H₂O_(l)

Mole ratio 1 :1

0.5M 0.5M

25 x 0.5 = 0.0125 moles

1000

(c) Mole ratio

NaOH : HCl = 1 :1

Molarity of NaOH is 0.5M

Table II

Marking should be done as in table 1.

Calculations

(a) ) Titre 1 + Titre II + Titre III = Answer

3

(b) 1000 = 0.5moles

100cm³ = ?

100 x 5 = 0.05moles

1000

100cm³ = 0.05moles

25cm³ = ?

25 x 0.05

100

= 0.0125moles

(c) mole ration 1:2

Moles of carbonate = ½ x 0.0125 = 0.00625moles

(d) 125

Question 2

Table III

Marks should be distributed as follows :

(i) Complete table

– Incomplete table with more than 5value ½mk

(ii) Decimal

• Accept whole numbers for time
  

– ¹/_t must be decimals not fractions

(iii) Trend in time

• Accept reducing values for time
  

(iv) Trend in ¹/_t

(b) The value given must shown on the graph

– Conversion of 318K to ^oC is very important before reading form the graph.

GRAPH

• Labeleling ½ mk for both axes
  
• Scale ½ k (at least ¾ pg)
  
• Plotting 1mk
  
• Shape 1mk (should be a curve)
  

(c) As the temperature is increased the time taken for the reaction to take place is reduced

due to high collision of particles hence the rate of reaction will be high.

Rate of reaction is directly proportional to increase in temperature.

Question 3

Procedure 1

Procedure 2