SOTIK DISTRICT CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS

SOTIK DISTRICT CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL  

Requirements:

In addition to the equipment, apparatus and chemical found in the chemistry

laboratory each candidate will require the following:  

• About 100cm³ of solution L
  
• About 100cm³ of solution N
  
• A burette
  
• A pipette
  
• 3 conical flasks
  
• 4.0g of solid K
  
• Thermometer
  
• Distilled water
  
• Test tube holder
  
• 3 boiling tubes
  
• Phenolphthalein indicator
  
• Filter paper
  
• Filter funnel
  
• Source of heat
  
• 1g of solid x
  
• 10ml measuring cylinder
  
• 2M HNOз
  
• Seven test tubes
  
• Stirring rod
  
• 2M NaOH
  
• 2M NH₄OH
  
• 2M HCL
  
• 0.5M lead (II) nitrate
  
• 0.5M barium chloride
  

NOTES

-Solution L is prepared by dissolving 5g of NaOH in a litre of distilled water

-Solution N is prepared by dissolving 9.84g of C₂H₂O₄.2H₂O in a litre of distilled water (oxalic acid)

-Solid K is potassium chlorate

-Solid X is a mixture of copper (II) oxide and zinc sulphate in the ratio 1:1

1.  You are provided with:-  

(i) Solution L containing 5g per litre of sodium hydroxide

(ii) Solution N containing 9.84g per litre of oxalic crystals of formula C₂H₂O₄.X H₂O  

(iii) You are required to determine the number of moles of water of crystallization X in

one mole of oxalic acid (C₂H₂O₄. XH₂O)

(iv) You are required to determine the number of moles of water of crystallization X; in one

mole of oxalic acid (C₂H₂O4. XH₂O)  

Procedure

(i) Fill the burette with solution N.

(ii) Pipette 25cm³ of solution L into 250cm³ conical flask and add 2 drops of phenolphthalein

indicator to it and titrate with solution N.

(iii) Record your results in the table below  

(iv) Repeat the experiment twice to obtain consistent readings and complete the table  

Table 1

(a) Calculate the average volume of solution N used

 (b) Determine:-

(i) The concentration of sodium hydroxide in one litre of solution L

(Na =23, O= 16, H= 1)

(ii) Write the equation of the reaction taking place

(iii) The number of moles of anhydrous carbohydrates oxalic acid in one litre of the

solution N  

(iv) The relative formula mass of anhydrous oxalic acid, solution N (C = 12, H=1, O = 16) (v) The number of moles of water of crystallization in one mole of oxalic acid

2.  You are provided with solid K, a boiling tube and a thermometer. You are required to determine the solubilities of solid K, at various temperatures.

Procedure:-  

1. Carefully transfer all the 4.0g of solid K into a clean boiling tube and add 10cm³ of distilled water from a burette.  

(b) Heat the boiling tube and its contents gently with shaking until all the solid dissolves.

(Do not spill the solution during heating.) Stop heating when all the solid dissolves.

See the diagram below:-  

(c) Gently stir the solution using the thermometer and record the temperature at which

crystals appear. (The crystals appear as small shining particles)

(d) Using a burette add 2.5cm³ of water to the solution and heat until all the solid dissolves.

  Repeat procedure(c)

(e) Repeat the experiment each time adding 2.5cm³ of distilled water from a burette.

Record the results in the table below:-  

(i) Complete the table by filling in the row for solubility of K and temperature at

which crystals appear

(ii) On the grid provided, draw the graph of solubility of K versus temperature  

(iii) At which temperature is solubility 24/100g of water?  

(iv) If a solution containing 30g of K at 85^oC is cooled to 60^oC

 (a) At which temperature will crystals first appear?

 (b) What would be the total mass of the crystals obtained when the solution finally

cools to 60^oC  

 (c) What is the solubility of K at 75^oC  

3.  You are provided with solid X which is a mixture of two solids. Carry out the following tests

to identify the cations and anions present in the mixture.

(a) Add about 10cm³ of water, stir and then filter. Keep both the residue and the filtrate for

further reactions.2O)

P

(b) Place the residue in a boiling tube and add dilute nitric acid and warm. Divide the solution

  into two portions  

 (c) To the 1^st portion add NaOH_(aq) till in excess

(d) To the 2^nd portion add aqueous ammonia till in excess

(e) Divide the filtrate into 5 portions. To the 1^st portion add dilute HCl

(f) To the 2^nd portion add lead (II) Nitrate solution

(g) To the third portion add Barium Chloride solution

(h) To the 4^th portion add sodium hydroxide solution till in excess  

(i) To the 5^th portion add aqueous ammonia till in excess

SOIK DISTRICT CHEMISTRY PRACTICAL ANSWERS

1.  TABLE I

a)Complete table penalize ½ for inverted table and arithmetic errors

b) Use of decimal tied to the 1^st and 2^nd rows  

c) Accuracy ±0.2 s.v √
^½
± 0.1 sv√1

d) Principles of averaging as shown below

e) Final answer ± 0.2s.v ± 0.1 s.v√1  

a)T₁+T₂+T₃√
^½

3

= correct answer√
^½ (2d.place) (transferred to the table)

b)i)  5
√ ^½

  40

=0.125 moles per litre

  ii)COOHCOOH_(aq) + 2 NaH_(aq) COONaCOONa_(aq) +2H₂O_(l)√
^½ balanced  

√
^½ s.symbols

OR

  C₂H₂O_4(aq) +2 Na₂O_4(aq) +C₂Na₂O₄(aq) 2H₂O(l)

iii) Moles of NaOH = 25X0.125
√

  1000

  = 0.003125

 Moles of C₂H₂O₄ = 0.003125 X 1

  2

  = 0.0015625

Ans in (a) 0.00015625

1000cm³ 1000×0.0015625 √^½

Ans in (a)

= Correct answer √^½

V) C₂H₂O₄ X H₂O = answer in (iv) √^½

18x = Ans (iv) – 90√^½

  x = Ans (iv) – 90
√^½

  18

 = Correct answer √^½ (whole number)  

2.  Table 1

• ½ mk each correct entry
  
• Penalize 1 mk if 1 d. place is not used consistently in the last row.
  
• Penalize ½ mark for temperature below 400c and 1000c to a maximum of 1mark.  
  
• Penalize 1 mark if there is no trend.
  

(ii) Graph

• Labeling (½ mark) – Title, axes, correct units.
  
• Scale (½ mark) – more than on both axes.
  
• Plotting (1mark) – All points plotted correctly.
  
  • Curve(1mark) – Smooth curve passing through at least 3 correctly plotted points.
    

(iii) ½ mark

1. 1 mark
   
2. 1mark Read from candidates graph and credited only if within  0.1 the S.V
   
3. 1 mark
   

3.   (a)