STANDARD GRADE CHEMISTRY CALCULATIONS

Calculation of empirical composition.

The formula of compounds can be determined by experiment. The empirical formula is the simplest formula of the compound.

Worked example.

Analysis of an oxide of copper shows that it contains 3.175 g of copper and 0.4 g of oxygen. What is the empirical formula of this compound?

Step 1. Write the symbols for the elements Cu O

Step 2. Show the mass,or percentage, of each element. 3.175 0.4

Step 3. Divide each by the R,A.M. of the element

= 0.05 0.025

3.175

63.5

0.4

16

Step 4. Divide each answer by the smallest

= 2 1

0 .05

0.025

0 .05

0.025

Step 5. Write the formula Cu2O

Calculation of empirical composition.

Calculations for you to try.

1. Calculate the empirical formula for the compound which contains 2.40g of carbon and 0.60g of hydrogen.

Symbols of the elements C H

Mass of each element 2.400.60

Divide each by its RAM 2.40/12 0.60 /1

= 0.2 0.6

Divide each answer by smallest 0.2/ 0.2 0.60 /0.2

= 1.0 3.0

Empirical formula = CH3.

Standard Grade Chemistry

Standard Grade Chemistry

2. Analysis of a compound showed that it contained 40% calcium,

12% carbon and 48% oxygen by mass.

Calculate the empirical formula of the compound.

Symbols of the elements Ca C O

% of each element 40 12 48

Divide each by its RAM 40/40 12 /12 48/16

= 1 1 3

Empirical formula = CaCO3.