Laws of Chemical Combination

Law of Conservation of Mass

Law

There is no measurable change in the mass during a chemical reaction

The sum of the masses of reactants is equal to the sum of the masses of the products

Example

How many grams of carbon dioxide are formed when 12.0 g of carbon combine with 32.0 g of oxygen?

solution


12.0 g	32.0 g	44.0 g

Example

If 5.0 g of magnesium is burned producing 6.0 g of magnesium oxide, what mass of oxygen was used?

solution


5.o g	1.0 g	6.0 g

Note the bold characters; to balance the , there must be

Law

Every compound has a fixed elemental composition by mass

Calculations are probably common sense

We can use experimental data

Example

A sample of water decomposes to form of oxygen and of hydrogen. Find the percentage of hydrogen and oxygen in of water.

solution

In absence of experimental data, we can use molar mass:

Example

Determine the percentage composition of oxygen in potassium chlorate () (List of Polyatomic Ions)

solution