Chemistry: Law of Conservation of Mass and Law of Constant Proportions

Laws of Chemical Reactions

• The law of conservation of mass states that mass cannot be created or destroyed in a chemical reaction.

Law of Constant Proportions

• Many compounds are composed of two or more elements in the same proportions, regardless of their source or preparation method.
• The ratio of the mass of hydrogen to the mass of oxygen in water is always 1:8, regardless of the source of water.
• Similarly, in ammonia, nitrogen and hydrogen are always present in the ratio 14:3 by mass, regardless of the method or source.

Atomic Theory

• John Dalton's atomic theory states that the smallest particles of matter are atoms, and that elements are always present in definite proportions by mass in a chemical substance.

Chemical Formulae

• A chemical formula represents the composition of a compound in terms of the symbols of the elements present.
• The formula of calcium hydroxide is Ca(OH)2, indicating two hydroxyl (OH) groups joined to one calcium atom.

Molecular Mass

• Molecular mass is the sum of the atomic masses of all the atoms in a molecule of a substance, expressed in atomic mass units (u).
• Examples of molecular mass calculations include water (H2O) and nitric acid (HNO3).

Formulae of Compounds

• The formula of sodium carbonate is Na2CO3.
• The formula of ammonium sulphate is (NH4)2SO4.

Exercises

• Write down the formulae of: • Sodium oxide • Aluminium chloride • Sodium sulphide • Magnesium hydroxide

Test your knowledge of the fundamental principles of the law of conservation of mass and the law of constant proportions in chemistry. Understand the concepts behind mass conservation and the consistent proportions of elements in compounds.