Question 1
D is 0.050 mol dm-3 HCl.
E is a saturated solution of Ca(OH)2 at room temperature
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Put D into the burette and titrate it against 20.0 cm3 or 25.0 cm3 portions of E using methyl orange as indicator. Repeat the titration to obtain concordant titre values.
Tabulate your results and calculate the average volume of D used.
The equation for the reaction is:
Ca(OH)2 + 2HCl → CaCl2 + 2H2O -
From your results and the information provided, calculate the solubility of Ca(OH)2 at room temperature in:
- moles per dm3 (mol dm-3);
- grammes per dm3 (g dm-3).
- What volume of distilled water must be added to 500 cm3 of E in order to reduce the concentration of ca2+ ions to one quarter of its original value? [H = 1.0, O = 16.0, Ca = 40.0]
Observation
This question was well attempted, and performance of the candidates was good.
In part (a), majority of the candidates correctly carried out the titration experiment.
In part (b), majority of the candidates were able to calculate the solubility of Ca(OH)2 at room temperature.
In part (c), majority of candidates were able to determine the volume using C1V1 = C2V2.
The expected answers include:
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Two concordant titres = 8 marks
Averaging = 2 marks
(c).
