Question 1A
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.
- 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:
- concentration of B in moldm-3;
- concentration of A in moldm-3;
- number of mole of Fe2- in the volume of B pipetted.
[ FeCl2 = 127 gmol-1 ][20 marks]
Observation
In part (a), majority of the candidates tabulated the titration table correctly and calculated the volume of A used.
In part (b), majority of the candidates calculated the concentrations of A and B in moldm-3 correctly. Some candidates lost marks to wrong unit while majority of them did not understand the concept of mole ratio.
The expected answers include:
(a) Two concordant titres = 8 marks
Averaging = 2 marks
