Question 1A
A is 0.200 moldm3 of HCl.
C is a solution containing 14.3g of Na2CO3. XH2O in 500 cm3 of solution.
- Put A into the burette and titrate it against 20.0 cm3 or 25.0 cm3 portions of C using methyl orange as indicator. Repeat the titration to obtain consistent titre values.
Tabulate your results and calculate the average volume of A used.
The equation for the reaction is:
- From your results and the information provided, calculate the
(i) concentration of C in moldm-3;
(ii) concentration of C in gdm-3
(iii) molar mass of Na2CO3. xH2O;
(iv) the value of x in Na2CO3 . xH2O
[ H = 1.0; C = 12.0; O = 16.0; Na = 23.0] [21 marks]
Observation
This question tested the skills of acid – base titration. Majority of the candidates responded to the question.
In part (a), majority of the candidates were able to carry out the titration. In addition, they were able to determine the average volume of acid used
In part (b), majority of the candidates calculated the concentration of substance C in moldm-3 and in gdm-3 respectively. However, some candidates lost marks to their inability to round off their answers to three significant figures. They equally lost marks to wrong units.
Expected answers include:
(a) Two consistent/ concordant titres
Averaging
(b)