Question

Prove law of conservation of mass.

Answer 1

The law of conservation of mass, states that during a chemical reaction, the total mass of the products must be equal to the total mass of the reactants. In other words, mass cannot be created or destroyed during a chemical reaction but is always conserved.

As an example, consider the reaction between silver nitrate and sodium chloride.

AgNO₃(aq)+NaCl(aq)⟶NaNO₃(aq)+AgCl↓

• These two compounds will dissolve in water to form silver chloride and sodium nitrate. The silver chloride does not dissolve in water, so it forms a solid that we can filter off.
• When we evaporate the water, we can recover the sodium nitrate formed. If we react 58.5 grams of sodium chloride with 169.9 grams of silver nitrate, we start with 228.4 grams of materials.
• After the reaction is complete and the materials are separated, we find that we have formed 143.4 grams of silver chloride and 85.0 grams of sodium nitrate, giving us a total mass of 228.4 grams for the products.
• So, the total mass of reactants equals the total mass of products, proof of the law of conservation of mass.