To find a percent: part X 100 Percent Composition To find a percent: part X 100 whole 1) Find the mass of each element in the compound and multiply masses by subscripts. (Find molar mass) 2) Divide by the total mass of the compound 3) Multiply by 100 to get percent Total mass of element X 100 Total mass of compound

Example 1 What percent of copper is in the compound Cu2S? Cu=2 x 63.55= 127.1 S= 1 x 32.07= 32.07 159.17 g 127.1 g x 100= 79.85 % Cu

Example 2 What percent of each element is in barium phosphate? HINT: YOU HAVE TO WRITE THE FORMULA FIRST!!! Remember the percentage should add up to 100

Example 2 Ba+2 PO4 -3 Ba3(PO4)2 write formula first Ba=3 x 137.328= 411.984 P= 2 x 30.974= 61.948 O= 8 x 15.999= 127.992 601.924g 411.984 x 100= 68.4% Mg 61.948 x 100 = 10.3% P 601.924 601.924 127.992 x 100 =21.3% O 601.924

Try these on your own Find the percent for all elements CuBr2 NaOH (NH4)2S N2S2 KMnO4