Question #67109

1 Answer
Stefan V.
May 15, 2015

The percent of aluminium in aluminium sulfate, #Al_2(SO_4)_3#, is 15.8%.

The percent composition of aluminium in aluminium sulfate refers to the amount of aluminium you get for every 100 g of aluminium sulfate.

You get the amount of aluminium by using moles and molar masses. Notice that 1 mole of #Al_2(SO_4)_3# dissociates to produce 2 moles of aluminium cations

#Al_2(SO_4)_3 -> color(red)(2)Al^(3+) + 3SO_4^(2-)#

This means that you have

#(color(red)(2) * 26.9815 cancel("g/mol"))/(342.15cancel("g/mol")) * 100 = color(green)("15.8%")#, where

#"26.9815 g/mol"# - the molar mass of aluminium;
#"342.15 g/mol"# - the molar mass of aluminium sulfate.

This means that you get 15.8 g of aluminium for every 100 g of aluminium sulfate.

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