Question

Which of the following laboratory procedures best illustrates the law of conservation of mass?

Recording the rise in water level when a 25 g piece of wood is placed in 200 mL of water
Synthesizing 36 g of H2O plus leftover reactants by combining 4 g of H2 and 32 g of O2
Heating 32 g of S and 56 g of Fe to form 80 g of FeS plus unused reactants
Measuring precisely 0.495 g of sulfur powder

Answer 1

Synthesizing 36 g of H2O because the mass of the reactants add up to the mass of the product

Answer 2

Answer is: Synthesizing 36 g of H2O plus leftover reactants by combining 4 g of H2 and 32 g of O2.

m(H₂) + m(O₂) = m(H₂O).

4 g + 32 g = 36 g.

Conservation of mass: during chemical reaction no particles are created or destroyed, the atoms are rearranged from the reactants to the products.

Balanced chemical reaction: 2H₂ + O₂ → 2H₂O.

m(H₂) = 4 g; mass of hydrogen.

n(H₂) = 4 g ÷ 2 g/mol.

n(H₂) = 2 mol; amount of hydrogen.

m(O₂) = 32 g.

n(O₂) = 32 g ÷ 32 g/mol.

n(O₂) = 1 mol; amount of oxygen.

n(H₂) : n(O₂) = 2 mol : 1 mol according to balanced chemical reaction.