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Question

Aluminum can be determined gravimetrically by reaction with a solution of 8-hydroxyquinoline (C9H7NO). The net ionic equation is:

Al³⁺ (aq) + 3C₉H₇NO^- (aq) = Al(C₉H₆ON)₃ (s) + 3H⁺ (aq)

A mass of 18.29 g of Al(C₉H₆ON)₃ (459.45 g/mol) was obtained by precipitating all of the Al³⁺ from a solution prepared by dissolving 4.91 g of a mineral. What is the mass percent of aluminum (26.98 g/mol) in the mineral sample?

Answer 1

Al³⁺ (aq) + 3C₉H₇NO^- (aq) = Al(C₉H₆ON)₃ (s) + 3H⁺ (aq)

moles Al(C₉H₆ON)₃ (s) = 18.29 g x 1 mol / 459.45 g = 0.03981 moles

moles Al = 0.03981 mols Al(C₉H₆ON)₃ (s) x 1 mol Al / 1 mol Al(C₉H₆ON)₃ (s) = 0.03981 mols Al

grams Al = 0.03981 mols Al x 26.98 g Al / mol Al = 1.074 g Al

% by mass Al = 1.074 g / 4.91 g (x100%) = 21.9% (to 3 sig. figs.)