A 4.78-g sample of aluminum completely reacts with oxygen to form 6.67 g of aluminum oxide. What is the mass percent composition of aluminum in aluminum oxide?

1 Answer
Oct 30, 2015



The percent composition of aluminium in the

resulting oxide will be the ratio between the mass of aluminijm and the total mass of the oxide, multiplied

by #100#.

#"% Al" = m_"Al"/m_"oxide" xx 100#

In your case, you know that a #"4.78-g"# sample of aluminium reacts completely with excess oxygen to form an

unknown aluminium oxide.

Moreover, you know that this oxide has a mass of #"6.67 g"#.

Since all the luminium that initially reacted with the oxygen is now a part of the oxide, you can say that its

percent composition in the oxide will be

#"% Al" = (4.78color(red)(cancel(color(black)("g"))))/(6.67color(red)(cancel(color(black)("g")))) xx 100 = 71.664%#

Rounded to three sig figs, the

answer will be

#"% Al" = color(green)(71.7%)#