**(sometimes the percentage may not add up to 100% because of the rounding. If the percent is somewhere near 99.9% its ok.)**

**Ex.1 What is the percentage composition of NaCl?**

First we need the following:

Total Molar Mass of NaCl: 58.5g/mol

Molar Mass of Na: 23.0 g/mol

Molar Mass of Cl: 35.5 g/mol

Then we do the calculations like so:

% of Na =

__23 g/mol__x 100% = 39.3%

58.5 g/mol

% of Cl =

__35.5 g/mol__x 100% = 60.7%

58.5 g/mol

Total percentage: 100%

**Ex.2 What is the percentage composition of ZnSO3?**

Total Molar Mass of ZnSO3: 145.5 g/mol

Molar Mass of Zn: 65.4 g/mol

Molar Mass of S: 32.1 g/mol

Molar Mass of O: 16.0 x 3 = 48.0 g/mol

% of Zn =

__65.4 g/mol__x 100% = 44.9 %

145.5 g/mol

% of S =

__32.1 g/mol__x 100% = 22.1%

**145.5**

**g/mol**

% of O =

__48.0 g/mol__x 100% = 33.0%

145.5 g/mol

Total percentage: 100.0%

**Ex. 3 What is the percentage composition of Zn3(PO4)2?**

Total Molar Mass of Zn3(PO4)2: 386.2 g/mol

Molar Mass of Zn3: 65.4 x 3 = 196.2 g/mol

Molar Mass of P: 31.0 x 2 = 62.0 g/mol

Molar Mass of O: 16.0 x 8 = 128.0 g/mol

% of Zn =

__196.2 g/mol__x 100% = 50.8%

386.2 g/mol

% of P =

__62.0 g/mol__x 100% = 16.1%

386.2 g/mol

% of O =

__128.0 g/mol__x 100% = 33.1%

386.2 g/mol

Total percentage: 100%

**Ex. 4 If a compound contains 54 grams of Al, 36 grams of C, 56 grams of N, some amount of O, and has a total molar mass of 226 grams, what is the percentage composition?**

First, we need to find the molar mass of the amount of O. To do this we do:

226 - 54 - 36 - 56 = 80 <--- this is the molar mass of O.

% of Al =

__54.0 g/mol__x 100% = 23.9%

226.0 g/mol

__% of C =__

__36.0 g/mol__x 100% = 15.9%

226.0 g/mol

% of N =

__56.0 g/mol__x 100% = 24.8%

226.0 g/mol

% of O =

__80.0 g/mol__x 100% = 35.4%

226.0 g/mol

Total percentage: 100%

**Ex. 5 If a compound contains 21.6 grams of B, 57.0 grams of F, 80.8 grams of Ne, some amount of He, and has a total molar mass of 179.4, what is the percentage composition?**

What is the molar mass of He?

179.4 - 21.6 - 57.0 - 80.8 = 20 <--- this is the molar mass of He.

% of B =

__21.6 g/mol__x 100% = 12.0%

179.4 g/mol

% of F =

__57.0 g/mol__x 100% = 31.8%

179.4 g/mol

% of Ne =

__80.8 g/mol__x 100% = 45.0%

179.4 g/mol

% of He =

__20.0 g/mol__x 100% = 11.1%

179.4 g/mol

Total percentage: 99.9%

(In this case, the total percentage was not 100% but was 99.9%. It is just a 0.1% difference and not that big of a deal. This is the result due to rounding.)

Video similar to Ex 2 & 3:

Video almost similar to Ex. 4 & 5

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