Answer to Question #224551 in General Chemistry for thor#5684

Question

25.00 mL of an aqueous 0.10 M CaCO₃ solution is titrated with a 0.20 M HCl solution at room temperature, using methyl orange as the indicator. The color of the solution changed from the initial yellow color to a shade of orange when 23.15 mL of the titrand was added.

a).    Using the above titration result, explain the difference between the endpoint and equivalence point for a titration.

b).   Aqueous solutions of CaCO₃ are considered as primary standards while HCl solutions can be used only as secondary standards. Briefly explain why.

What will be the volume of HCl required for the above titration if phenolphthalein was used as the indicator? Write balanced chemical equations for the titration

Answer 1

The point in the titration process where the chemical reaction in the titration mixture ends is called equivalence point. The point in the titration process which is indicated by color change of the indicator is called endpoint. It is the point where the analyte has completely reacted with the titrant.

A primary standard is one which is prepared to a known concentration with a high degree of precision and confidence.

$Volume= 23.15$

CaCO₃ (s) + 2 HCl (aq) → CaCl₂ (aq) + H₂O (l) + CO₂ (g)