Percent Composition Worksheet



How to find the Percent Composition of a Substance!

Example 1:

To find the percent composition of red M&M’s in a bag of 200 M&M’s, if there are 26 red, you would use this formula.

Mass of Sample x 100 = Percent Composition

Total mass in the sample

So, in the M&M’s problem:

26 red x 100 = 13%

200 total

Example 2:

Find the percent composition of copper (Cu) in CuBr2.

Mass of Cu in the compound x 100 = Percent Composition

Total Mass of CuBr2 Compound

63.546 grams x 100 = 28.4%

223.354 grams

Percent Composition Practice

Find the percent compositions of all of the elements in the following compounds:

1) CuBr2

Cu: ___________

Br: ___________

2) NaOH

Na: ___________

O: ___________

H: ___________

3) (NH4)2S

N: ___________

H: ___________

S: ___________

4) N2S2

N: ___________

S: ___________

5) KMnO4

K: ___________

Mn: ___________

O: ___________

6) HCl

H: ___________

Cl: ___________

7) Mg(NO3)2

Mg: ___________

N: ___________

O: ___________

7) (NH4)3PO4

N: ___________

H: ___________

O: ___________

P: ___________

8) Al2(SO4)3

Al: ___________

S: ___________

O: ___________

Percent Composition Worksheet – Answer Key

Find the percent compositions of all of the elements in the following compounds:

1) CuBr2

Cu: 28.4%

Br: 71.6%

2) NaOH

Na: 57.5%

O: 40.0%

H: 2.5%

3) (NH4)2S

N: 41.1%

H: 11.8%

S: 47.1%

4) N2S2

N: 30.4%

S: 69.6%

5) KMnO4

K: 25%

Mn: 35%

O : 40%

6) HCl

H: 3%

Cl: 97%

7) Mg(NO3)2

Mg: 16%

N: 19%

O: 65%

8) (NH4)3PO4

N: 28%

H: 8%

O: 43%

P: 21%

8) Al2(SO4)3

Al: 16%

S: 28%

O: 56%

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