State law of reciprocal proportion with an example.

Law of reciprocal proportions

• The ratio of the masses in which two different elements combine separately with a fixed mass of a third element is either the same as or a simple multiple of the ratio of the masses in which they combine.

Example

• The methane is formed when $3\mathrm{g}$ of carbon reacts with $1\mathrm{g}$ of hydrogen.
• Water is formed when $8\mathrm{g}$ of oxygen reacts with $1\mathrm{g}$ of hydrogen to form water.
• Their ratio masses is $\mathrm{C}:\mathrm{O}=3:8$
• Carbon dioxide is formed when $12\mathrm{g}$ of carbon reacts with $32\mathrm{g}$ of oxygen.
• Their ratio masses is $\mathrm{C}:\mathrm{O}=12:32=3:8$
• When carbon and oxygen combine, their mass ratios are equal to when they do so separately with a constant mass of hydrogen.