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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  

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(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

Titration

1

2

3

Final burette reading (cm3)

   

Initial burette reading (cm3)

   

Volume of solution N used (cm3)

   

 

(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:-  

Total volume of water (cm3)

10.00

12.50

15.00

17.50

20.00

22.50

Mass of solid K (g)

4.00

4.00

4.00

4.00

4.00

4.00

Solubility of K in g/100g of water

40.00

  

22.90

 

17.78

Temperature at which crystals appear ( oC)

      

(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 85oC is cooled to 60oC

 (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 60oC  

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

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 1st portion add NaOH(aq) till in excess

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

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


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

(g) To the third portion add Barium Chloride solution

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

(i) To the 5th 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 1st and 2nd 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

  C2H2O4(aq) +2 Na2O4(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) – 90½

  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)

Observations

Inferences

  • Black residue √½
    • Colourless solution as filtrate √½

X

(b)

  • Blue solution formed√½
  • No effervescence √½

 

CU2+ may be present √½

HCO3 , CO 3½ absent the two

(c )

  • Blue ppt √½
  • Insoluble in excess √½

 

CU 2+ may be present √½

(d)

  • Blue ppt½
  • Soluble to give a deep blue solution½

 

CU 2+ Present

(e) – No white ppt 1

Image From EcoleBooks.comImage From EcoleBooks.comAg+ pb 2+ absent ( for two) CO3 HCO
3  

(f) – White ppt ½

Image From EcoleBooks.comCl , SO4 may be present 1

(g) – White ppt ½

SO4 present ½

 

(h) – White ppt ½

– Soluble in excess √½

Image From EcoleBooks.com

Zn,  Al3+ may be present

(i) – White ppt ½

– Soluble in excess

Zn 2+ Present.

 


 




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