A laboratory technician receives a 4.000 g sample of a white crystalline solid that…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A laboratory technician receives a 4.000 g sample of a white crystalline solid that is thought to be primarily sodium chloride (NaCl) contaminated with a small amount of insoluble silica (SiO2). The technician dissolves the entire sample in distilled water, filters the mixture, dries the residue thoroughly, and records a mass of 0.250 g for the solid remaining on the filter paper.
(a) Describe, in prose form, the chemical reasoning that allows the technician to use the filtration data to assess the composition of the original sample.
(b) Calculate the mass percentage of sodium chloride in the original sample, reporting your answer to the correct number of significant figures.
(c) Identify one key assumption inherent in the procedure that could lead to systematic error if it is violated, and explain how that violation would affect the calculated percent purity.
(d) Propose an additional experimental test or measurement that could be performed on the filtrate to provide supporting evidence for the calculated percent purity. Justify how the results of your proposed test would confirm or challenge the value obtained in part (b).