Thursday, January 24, 2013Percent Composition

Students will be able to:Calculate the percent composition of

chemical compounds.

The percent composition tells us the % by mass of each type of element in a compound.

To find % comp by mass, you take the mass of the element in the compound and divide by the total mass of the compound

the percentage by mass of each element in a compound

100compound of mass total

element of masscomp %

First Determine molar mass of Cu2SCu: 2x 63.5 = 127S: 1 x 32 = 32 mass = 159g/mol

Find the % composition of Cu2S.

%Cu =2*63.5 g Cu159 g Cu2S

100 =79.8% Cu

100 =%S =32 g S

159 g Cu2S 20.2% S

How many grams of copper are in a 38.0-gram sample of Cu2S?

(38.0 g Cu2S)(0.798) = 30.3 g Cu

Cu2S is 79.8% Cu

100 =%H2O = 36.0 g147.0 g

24.5%H2O

Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O?

Determine the percent composition of Mn(SO4)2.

How many grams of manganese are in a 500g sample of Mn(SO4)2?

What percent of PO5 is phosphorous?