Question

A hydrated salt contains Cu = 25.50%, S = 12.90%, O = 25.60% and the remaining % is water of crystallization. Calculate the empirical formula of the salt. [Cu = 64, S = 32, O = 16, H = 1]

August 2, 2024

Answer

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Cu	25.50	64	= 0.398	= 1
S	12.90	32	= 0.403	= 1.01 = 1
O	25.60	16	= 1.6	= 4.020 = 4
H₂O	100 – (25.50 + 12.90 + 25.60) = 36	18	= 2	= 5.025 = 5

Hence, Simplest ratio of whole numbers = Cu : S : O : H₂O = 1 : 1 : 4 : 5

Hence, empirical formula is CuSO₄.5H₂O

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