TRANS MARA DISTRICT CHEMISTRY PRACTICAL QUESTIONS

CONFIDENTIAL

INSTRUCTIONS

Each candidate should have :

• 80 cm³ of solution T
  
• 100 cm³ of solution S
  
• Exactly 1.5g of solid V
  
• 250cm³ beaker (glass)
  
• 1 label
  
• 1 pipette
  
• 1 burette
  
• 100cm³ measuring cylinder
  
• 1.2g
  
• 120cm³ plastic beaker
  
• A stop clock /watch
  
• About 1.0g of solid J
  
• 1 boiling tube
  
• 1 metallic spatula
  
• 1 glass rod
  
• 5 test tubes
  
• 1 filter paper
  

Access to:

• Phenolphthalein
  
• 2m lead (II) nitrate
  
• 0.05 M sodium thiosulphate
  
• Distilled water
  
• 20% volume hydrogen peroxide
  
• Source of heat ( Bunsen burner)
  

Notes:

• 20% 20 volume peroxide is prepared by diluting 20cm³ of 20v hydrogen peroxide
  

to make 100cm³

• solution T is 1.0 hydrochloric acid and is made by dissolution 86cm³ of 35-37% hydrochloric acid diluted to 1litre of solution
  
• solution S is 0.5m sodium hydroxide
  
• solid V is exactly 1.5g of sodium carbonate ( anhydrous)
  
• solid J is potassium iodide
  
• solid M is 1.2g magnesium powder
  
• solution K is 0.02m copper (II) sulphate
  

1. You are provided with the following :

• 1.0M Hydrochloric acid; solution T.
• 0.5M sodium hydroxide; solution S
• Anhydrous sodium carbonate of unknown mass: solid V.

You are required to determine the mass of sodium. Carbonate that was used in the experiment.

Procedure

Measure 60cm³ portion of 1m hydrochloric acid using a measuring cylinder and transfer

it to 100cm³ beaker. Add all sodium carbonate (solid V) to the acid in the beaker and

stir gently. Leave the mixture for 3 minutes until there is no effervescence transfer

the mixture into a clean 100ml measuring cylinder and add distilled water to make

100cm³ of the solution. Transfer all the solution into 250cm³ beaker and shake

well, label this solution W.

Fill the burette with solution S.

Pipette 25.0cm³ of solution W and transfer to a conical flask. Add 2-3 drops of phenolphthalein indicator and titrate with solution S. Records your results in table I below.

Repeat the titration to get two more concordant values.

 Table I

Transfer the mixture into a clean 100ml- measuring cylinder and add distilled water to

make 100cm³ of the solution.

 (a) Determine the average volume of solution S used.

 (b). Calculate the number of moles of sodium hydroxide (solution S) used.

(c). Find the number of moles of hydrochloric acid in 25cm³ of solution W.

 (d). Determine the number of moles of hydrochloric acid in 100cm³

 (e). Calculate the number of moles of hydrochloric acid in the original 60cm³ of solution.

 (f). Calculate the number of moles of hydrochloric acid that reacted with sodium

carbonate.

(g). Determine the mass of sodium carbonate that reacted with the acid. (Na= 23, C= 12, 0= 16).

2. You are provided with the following.

 (i). 1.2g Magnesium powder, solid M

 (ii). 0.02M copper (ii) sulphate, solution K

You are required to determine the molar enthalpy of displacement for the reaction

between

magnesium powder and copper (II) sulphate solution.

Procedure

Measure out 100cm³ of solution K into a plastic beaker.

Measure the temperature of this solution at every minute for four minutes. Add the entire amount of solid M to the contents of the plastic beaker at the fourth minute. Stir with the thermometer. Record the temperature after every half-a- minute in table II below.

Table II

(a). Draw the graph of temperature (^oC) against time, t (in minutes) ) Use your graph to

get the temperature rise.

 (b). Calculate the heat lost by the solution

 (Specific heat capacity of solution = 4..2Jg ^-1K^-I, density of solution = 1g/cm³)

(c). Write an ionic equation for the reaction.

(d). Calculate the number of moles of :

(i). Copper (ii) ions in the original solution.

(ii). Magnesium added to the copper (ii) sulphate solution

(iii). Copper (II) ions displaced by magnesium powder.

(Mg = 24, Cu = 63.5, S = 32, O = 16)

(e). Calculate the molar heat of displacement of copper (II) ions by magnesium powder.

(f). Comment on the value of the molar heat if ion powder had been used instead magnesium

powder . Explain.

(a). (i)You are provided with solid J.

(ii). To the filtrate above, dip a clean metallic spatula and burn a drop of the filtrate

on it with a non-luminous flame.

(iii). Divide the filtrate into two equal populations.

I. To the 1^st portion add 2m lead (ii) nitrate.

II. To the second portion add 3 -5 drops of 20% 20 – Volume hydrogen peroxide

(iv). To the resulting mixture in (ii) above, add about 1cm³ of sodium thiosulphate

solution Q. From the tests carried out above identify.

(i). Cation

(ii). Anion