Question 1
1. Solution P is a sample of contaminated HCl. Solution Q is 0.100 moldm-3 NaOH. Titration of 25.0 cm3 portions of Q with P phenolphthalein as indicator gave the following results.
The results are recorded in the table below.
Burette readings / cm3 |
1 |
2 |
3 |
Final reading |
|
44.30 |
34.80 |
Initial reading |
0.00 |
- |
10.70 |
Volume of A used/cm3 |
24.80 |
24.60 |
|
- (i) Complete the table.
- From your results and the information provided, calculate the:
- concentration of HCl in P, in mol dm-3;
- amount of HCl in 6.15 dm3 of P
(ii) Calculate the average volume of A used.
Calculate the amount od calcium trioxocarbonate (IV) in grammes, needed to neutralize the 6.15 dm3 of P according to the following equation:
CaCO3(aq) + 2HCl(aq) CaCl2(aq) + H2O (l) + CO2(g)
[ Molar mass of CaCO3 = 100 ]
[15 marks]
Observation
This question was compulsory for all candidates. Candidates’ performance in the question was average.
In part (a), majority of the candidates were able to complete the titration table and calculate the average volume of P used.
In part (b), majority of the candidates could not calculate the concentration of HCl in P, in mol dm-3. Also, they could not calculate the amount of HCl in 6.15 dm3 of P.
In part (c), majority of the candidates could not calculate the amount of calcium trioxocarbonate (IV) in grammes, needed to neutralize the 6.15 dm3. of P.
The expected answers include:
(a) (i)
Burette Reading / cm3 |
1 |
2 |
3 |
Final Reading |
24.80 |
44.30 |
34.85 |
Initial Reading |
0.00 |
19.70 |
10.70 |
Volume of A used / cm3 |
24.80 |
24.60 |
24.10 |
(ii) From the equation of reaction:
(iii)
