Question

1. If 12.7 g of a substance reacts completely with 7.89 g of oxygen to form carbon dioxide and water, what mass of carbon dioxide is produced if 3.24 g of water is also produced?

2. A solid, pure substance containing just carbon and hydrogen is found to contain 24.4g of carbon and 3.07 g of hydrogen. How many grams of carbon will be in a 5.14 g sample of the solid?

Answer 1

1. According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.

So, 12.7 g of a substance + 7.89 g of oxygen = mass of carbon dioxide + 3.24 g of water

or, Mass of carbon dioxide = 12.7 g + 7.89 g - 3.24 g = 17.35 g

2. Mass of C = 24.4 g; Mass of H = 3.07 g; Percentage of C = 24.4/(24.4 +3.07) x 100= 88.82 %

In second sample, Mass of sample = 5.14 g; Percentage of C = 88.82 %

thus mass of C = (5.14 x 88.82)/100 = 4.57 g