Percent Composition Worksheet



Unit 2-Percent Composition

Percent composition is the percent by mass of each element found in a compound.

Example: What percent of iron(III) hydroxide, Fe(OH)3, is oxygen?

Step 1: Find the molar mass of the compound.

1 mol Fe = 55.85 g

3 mol O = 3 × 16.00 g = 48.00 g

3 mol H = 3 × 1.008 g = 3.024 g

Molar Mass Fe(OH)3 = 106.87 g/mo

Step 2: Find the percentage by dividing the part by the whole and multiplying by 100.

[pic]×100 % = 44.91% oxygen

Solve the following.

1. What percent of magnesium bromide, MgBr2, is magnesium?

2. What percent of glucose, C6H12O6, is carbon?

3. What percent of Zn3(PO4)2 is zinc?

4. What percent is Cu of CuCO3 is Cu?

5. What percent is of CuCl2 Cu?

6. What percent of AgNO3 is silver?

7. Which has the higher percent of aluminum, Al2O3 or Al(NO3)3?

8. Why is knowledge of percent composition important in the mining process?

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Part II-Find the percent compositions of all of the elements in the following compounds and name all compounds:

9) CuBr2

Cu: ___________

Br: ___________

10) NaOH

Na: ___________

O: ___________

H: ___________

11) (NH4)2S

N: ___________

H: ___________

S: ___________

12) N2S2

N: ___________

S: ___________

13) KMnO4

K: ___________

Mn: ___________

O: ___________

14) HCl

H: ___________

Cl: ___________

15) Mg(NO3)2

Mg: ___________

N: ___________

O: ___________

16) (NH4)3PO4

N: ___________

H: ___________

O: ___________

P: ___________

17) Al2(SO4)3

Al: ___________

S: ___________

O: ___________

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