Question 11A 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]

Question

Accepted Answer

Element% compositionAt. wt.Relative no. of atomsSimplest ratioAl10.502710.5027\dfrac{10.50}{27}2710.50​ = 0.3880.3880.387\dfrac{0.388}{0.387}0.3870.388​ = 1K15.13915.139\dfrac{15.1}{39}3915.1​ = 0.3870.3870.387\dfrac{0.387}{0.387}0.3870.387​ = 1S24.83224.832\dfrac{24.8}{32}3224.8​ = 0.7750.7750.387\dfrac{0.775}{0.387}0.3870.775​ = 2O100 - (10.50 + 15.1 + 24.8) = 49.61649.616\dfrac{49.6}{16}1649.6​ = 3.13.10.387\dfrac{3.1}{0.387}0.3873.1​ = 8Simplest ratio of whole numbers = Al : K : S : O = 1 : 1 : 2 : 8Hence, empirical formula is AlKS2O8 or AlK(SO4)2

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

Stoichiometry — Percentage Composition — Empirical & Molecular Formula — Chemical Equations — Question 11

Question 11