Question 1A
A is a solution containing 5.00 g of HNO3 in 500 cm3 of solution.
B is a solution of NaOH of unknown concentration.
- Put A into the burette and titrate it with 20.0 cm3 or 25.0 cm3 portions of B using methyl orange as indicator. Repeat the titration to obtain concordant titre values. Tabulate your results and calculate the average volume of acid used.
- From your results and the information provided, calculate the:
- concentration of A in mol dm-3;
- concentration of B in mol dm-3;
- concentration of B in g dm-3;
- mass of NaNO3 formed, if 250 cm3 of NaOH were neutralized.
Equation of the reaction is:
HNO3 (aq) + NaOH (aq) NaNO3 (aq) + H2O (l)
{Molar mass of NaOH = 40 g mol-1; NaNO3 = 85 g mol-1]
Observation
In part (a), majority of the candidates correctly carried out the titration experiment. However, few of them could not tabulate their results well.
In part (b), majority of the candidates calculated the concentrations of A and B in mol dm-3 correctly. Also, majority of them also calculated concentration of B in g dm-3.
The expected answers include:
(a) Two concordant titres
Averaging(b)
(i)
(ii)
(iii)
(iv)
