1. Percent Composition

2. Molar Mass Calculate the Molar Mass of H 2 O 1 mole of H 2 O contains 2 mols H and 1 mol O. The mass of 2 moles H = 2 mol(1.008 g/mol)= 2.016 g The mass of 1 mole O = 1 mol(15.999 g/mol) = 15.999 g The mass of 1 mole of H 2 O = 15.999 g + 2.016g =18.015g The molar mass of H 2 O is 18.015 g/mol

3. Percent Composition What is the percent composition of Hydrogen in H 2 O? 2.016 g/mol 18.015 g/mol = 0.1119 x 100% = 11.19%

4. Important Factors What is the percent composition of Hydrogen in H 2 O? 2.016 g/mol 18.015 g/mol = 0.1119 x 100% = 11.19% 1.Significant figures 2.Units 3.Showing your work!!!!

5. Sig Fig rules again All zeros at the end after a decimal point are significant, leading zeros are never significant 0.0010 All nonzero numbers are significant 1234 All zeros between significant numbers are significant 1001 If there is a decimal point at the end all numbers are significant 1000. If there is no decimal point ending zeros are NOT significant 1000

6. Addition and Subtraction Sig Fig Rules When adding you keep the number of decimal places of the number with the smallest number of decimal places. 2.5 + 2.50 = 5.0 When multiplying your answer has to have the number of sig figs and the value with the least number of sig figs in the equation 2.5 x 2 = 5 not 5.0