Matter is neither created no destroyed in a chemical reaction. This means that in all reactions, mass of reactants is always equal to the mass of the products.

An experiment to prove the above law

• Aim: to illustrate the conservation of mass by reacting hydrochloric acid with sodium hydroxide solution
• Requirements: glass beaker, sodium hydroxide solution ,hydrochloric acid solution, test tubes ,bromothymol blue, weighing chemical balance
• Procedure:

• weigh a clean, dry glass beaker on a chemical balance
• pour 20ml sodium hydroxide solution into a beaker
• add a few drops of bromothymol blue solution to the contents of the beaker and record the colour
• add 20ml o hydrochloric acid solution to the contents of the beaker. If there is no colour change, add a few more drops of hydrochloric acid solution. Record the colour change, the final colour must be green.
• Record the final mass of the beaker

• Observation:

A white precipitate is observed as soon as the two liquids are mixed hence a salt called sodium chloride.

• Conclusions:

• The white precipitate shows the formation of a new substance as a result of the chemical reaction
• The weight of the new substance formed is equal to the original weigt taken before the reaction.
• This therefore means that there is no change of mass as the sodium hydroxide solution reacts with the hydrochloric acid solution.

NaOH(aq) + HCl (aq                             NaCl(aq) + H2O(l)