**ex. 1:**percent composition of AgOH (assume there is 1mol)

total MM (molar mass): 107.9 + 19.0 + 1.0 = 127.9

MM of Ag: 107.9 (same numerical value as the atomic mass)

MM of O: 16.0

MM of H: 1.0

% Ag: 107.9g/mol / 127.9g/mol x 100% = 84%

% O: 19.0g/mol / 127.9g/mol x 100% = 15%

% H: 1.0g/mol / 127.9g/mol x 100% = 1%

Check: 84% + 15% + 1% = 100%*

*the percentages should add up to or very close to 100%

**ex. 2:**percent composition of CO2 (assume there is 1mol)

total MM: 12.0 + 16.0(2) = 44.0g/mol

MM of C: 12.0g/mol

MM of O: 32.0g/mol

% C: 12.0g/mol / 44.0g/mol x 100% = 27.3%

% O: 32.0g/mol / 44.0g/mol x 100% = 72.2%

Check: 27.3% + 72.2% = 100%

**ex. 5:**percent composition of O in Cu2CO3

total MM: 123.5g/mol

MM of O: 48.0g/mol

% O: 48.0g/mol / 123.5g/mol x 100% = 39%

**ex. 4:**a compound contains 5.1 g of Cl, 22.0g of c, an unknown mass of O, & the total mass is 44.1g. Calculate % composition.

Mass of O: 44.1g-5.1g-22.0g = 17.0g

% Cl: 5.1g / 44.1 g x 100% = 11.6%

% O: 17.0g / 44.1g x 100% = 38.6%

% C: 22.0g / 44.1g x 100% = 49.9%

Check: 11.6% + 38.6 % + 49.9% = 100.1 %

Links to get you started:

http://chemistry.about.com/od/workedchemistryproblems/a/mass-percent-worked-problem.htm

http://www.ausetute.com.au/percentc.html

http://www.youtube.com/watch?v=qzUMKWhWKm8

**(THE BEST LINK!)**

http://www.youtube.com/watch?v=CSuZVJ8TA40&feature=related

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