2. Percentage composition Indicates the relative amount of each element present in a compound.

3. Calculating percentage composition Step 1 : Calculate molar mass Step 2 : Divide the subtotal for each element’s mass by the molar mass. Step 3: Multiply by 100 to convert to a percentage.

4. Example 1 1. Calculate the molar mass of water, H 2 O. Step 1 – H- 2(1.01)= 2.02 O – 1(16.0)= 16.0 ________ 18.02

5. Step 2 2.02/18.02 X 100 = 11.21% 16.0 /18.02 X 100 = 88.79 % Water is composed of 11.21 % hydrogen and 88.79 % oxygen.

6. Example 2 Calculate the percentage composition of sucrose, C12H22O11.

7. Determine the percent composition (or percent by mass of sodium carbonate.

8. Na 2 CO 3 Na – 2(23.0) = 46 C - 1(12.0) = 12 O - 3(16.0) = 48 -------- 106g

9. Determine the percent composition (or percent by mass of sodium carbonate. Na 2 CO 3 Na – 2(23.0) = 46.0 46/106 x 100 = 43.4% C - 1(12.0) = 12.0 12/106 x 100= 11.3% O - 3(16.0) = 48.0 48/106 x 100 = 45.3% -------- ---------- 106.0g 100%,

10. Determine the percent composition o0f sodium oxalate.

11. Na 2 C 2 O 4 Na - 2(23.0) = 46 C - 2(12.0) = 24 O - 4(16.0) = 64 -------- 134g

12. Determine the percent composition o0f sodium oxalate. Na 2 C 2 O 4 Na - 2(23.0) = 46 46/134 x 100= 34.3% C - 2(12.0) = 24 24/134 x 100= 17.9% O - 4(16.0) = 64 64/134 x 100=47.8% -------- --------- 134g 100%

13. Determine the percent by mass of aluminum oxide.

14. Al 2 O 3 Al - 2(27.0)= 54 54/102 x 100= 52.9% O - 3(16.0)= 48 48/102 x 100= 47.1% ------ 102g

15. Calculate the mass of bromine in 50.0 g of potassium bromide. KBr K – 1(39.1) 39.1/119.1 x 100 = 32.8% Br – 1(80.0) 80/119.1 x 100 = 67.2 % ----------- 119.1g

16. Br – 1(80.0) 80/119.1 x 100 = 67.2 % 50g x 0.672= 33.6 g of Bromine