WAEC Standard for Answering Chemistry Practical (Titration).

  A is a solution of potassium tetraoxomanganate (VII).
B is a solution of iron(II)chloride containing 4.80 g of the salt in 250 cm3 of solution.

  1. Put A into the burette. Pipette 20.0 cm3 or 25.0 cm3 of B into a conical flask, add 20.0 cm3 of H2SO4 (aq) and titrate with A. Repeat the titration to obtain concordant titre value.

Tabulate your results and calculate the average volume of A used.

The equation of the reaction is:

MnO4-(aq) +  5Fe2+ (aq) + 8H+ (aq)       –>        Mn2+(aq) + 5Fe 3+ (aq) +  4H2O (l)

(b) From your results and information provided, calculate the:

  1. concentration of B in moldm-3;
  2. concentration of A in moldm-3;
  3. number of mole of Fe2- in the volume of B pipetted.

[ FeCl2 = 127 gmol-1 ][20 marks]

The expected answers include:

(a)        Two concordant titres  = 8 marks
Averaging                   =  2 marks