A commercial washing soda sample that is advertised as "hydrated sodium carbonate" is…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A commercial washing soda sample that is advertised as "hydrated sodium carbonate" is suspected of containing a significant fraction of inert mineral filler. A 2.845 g portion of the sample is dissolved in water, and the resulting solution is diluted to exactly 250.00 mL. A 25.00 mL aliquot of this solution is titrated with 0.0500 M hydrochloric acid, requiring 23.35 mL of the acid to reach the phenolphthalein endpoint.
(a) Using the titration data, calculate the number of moles of hydrated sodium carbonate present in the entire 250.00 mL volumetric flask.
(b) Determine the mass of hydrated sodium carbonate (Na2CO3·10H2O) in the original 2.845 g portion.
(c) Compute the percent purity of the washing soda sample.
(d) The student inadvertently allowed some carbon dioxide from the air to dissolve in the titration mixture before beginning the titration. Predict qualitatively whether this error would cause the calculated percent purity to be too high, too low, or unaffected, and justify your prediction.
(e) Suggest one procedural change that would minimize the error discussed in part (d), and briefly explain why it would be effective.