How can I find the percent compositions of Al2(SO4)3?

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Answer 1 · 2014-05-29T00:01:58

To find the percent composition of Al₂(SO₄)₃, you divide the total mass of each atom by the molecular mass and multiply by 100 %.

% by mass = #"mass of component"/"total mass"# × 100 %

Mass of 2 Al atoms = 2 Al atoms × #(26.98"u")/(1"Al atom")# = 53.96 u.

Mass of 3 S atoms = 3 S atoms × #(32.06"u")/(1"S atom")# = 96.18 u

Mass of 12 O atoms = 12 O atoms × #(16.00"u")/(1"O atom")# = 192.0 u

Mass of 1 Al₂(SO₄)₂ formula unit = (53.96 + 96.18 + 192.0) u = 342.1 u

% of Al = #"mass of Al"/"total mass"# × 100 % = #(53.96"u")/(342.1"u")# × 100 % =15.77 %

% of S = #"mass of S"/"total mass"# × 100 % = #(96.18"u")/(342.14"u")# × 100 % =28.11 %

% of O = #"mass of O"/"total mass"# × 100 % = #(192.0"u")/(342.14"u")# × 100 % =56.12 %