Question

A salt has the following % composition — Al = 10.50%, K = 15.1%, S = 24.8% and the remaining oxygen. Calculate the empirical formula of the salt. [Al = 27, K = 39, S = 32, O = 16]

August 2, 2024

Answer

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Al	10.50	27	= 0.388	= 1
K	15.1	39	= 0.387	= 1
S	24.8	32	= 0.775	= 2
O	100 – (10.50 + 15.1 + 24.8) = 49.6	16	= 3.1	= 8

Simplest ratio of whole numbers = Al : K : S : O = 1 : 1 : 2 : 8

Hence, empirical formula is AlKS₂O₈ or AlK(SO₄)₂

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