NAME:______DATE:______

2.6 How do you calculate percent composition? AHS Instructor Ms. Kasia Room 109

UNIT 2 CHEMICAL BONDING: COVALENT

2.8 How do you calculate the percent composition of an element in a compound?

AIM:

DO NOW: Please answer the following Regents question to the best of your ability.

What is the gram-formula mass of Ca3(PO4)2?

A) 310 g/mol

B) 248 g/mol

C) 279 g/mol

D) 263 g/mol

ELEMENT / # of ELEMENTS / ATOMIC MASS / TOTAL MASS OF EACH

TOTAL MOLECULAR MASS OF THE COMPOUND:

PERCENT COMPOSITION

Definition:

Formula

STEPS for PERCENT COMPOSITION

RULE / DESCRIPTION / EXAMPLE: What is the percent composition of K2CO3
1
2
3
4
5

LET’S TRY SOME

1.  What is the percentage of oxygen in potassium chlorate (KClO3)?

2.  What is the percentage of chlorine in potassium chlorate (KClO3)?

3.  What is the percentage of potassium in potassium chlorate (KClO3)?

NAME:______DATE:______

2.8 How do we calculate the percent composition? AHS Instructor Ms. Kasia Room 109

UNIT 2 CHEMICAL BONDING: COVALENT

2.8 Independent Practice

1.  What is the percent by mass of carbon and oxygen in CO2?

2.  What is the percent by mass of oxygen in Fe2O3?

3.  What is the percent composition of both Aluminum and oxygen n in the compound Al2(SO4)3?

4.  A sample of a substance containing only magnesium and chlorine was tested in the laboratory and was found to be composed of 74.5% chlorine by mass. It the total mass of the sample was 190.2 grams, what was the mass of the magnesium?

a. 24.3 g c. 70.9 g

b. 48.5 g d. 142 g

Show your work here:

5. In which compound is the percent composition by mass of chlorine equal to 42%?

a. HClO (gram-formula mass = 52 g/mol)

b. HClO2 (gram-formula mass = 68 g/mol)

c. HClO3 (gram-formula mass = 84 g/mol)

d. HClO4 (gram-formula mass = 100 g/mol)

Show your work here: