Question

If 31.9 mg of a compound containing only carbon and hydrogen is burned in oxygen and yields 87.7 mg of CO₂ and 71.8 mg of H₂O, how much oxygen is used up?

O 100 mg
O 250 mg
O 127.6 mg
O 27 mg

Answer 1

To find out how much oxygen was used up, we use the conservation of mass. By subtracting the mass of the compound from the mass of the products, we find that 127.6 mg of oxygen was used up during combustion.

Step-by-step explanation:

To calculate the amount of oxygen used up during the combustion of a compound containing only carbon and hydrogen, we need to use the law of conservation of mass. This law states that mass is neither created nor destroyed in a chemical reaction. Therefore, the mass of the reactants (the compound containing carbon and hydrogen plus the oxygen) must equal the mass of the products (CO₂ and H₂O).

First, we need to convert the mass of CO₂ and H₂O from milligrams to grams to use the molar masses accurately. We have 87.7 mg of CO₂ and 71.8 mg of H₂O, which are 0.0877 g and 0.0718 g respectively. The total mass of the products is 0.0877 g + 0.0718 g = 0.1595 g.\

The original mass of the compound was 31.9 mg or 0.0319 g. Using the conservation of mass, if we subtract the mass of the original compound from the mass of the products, we get the mass of the oxygen that was used. So, 0.1595 g - 0.0319 g = 0.1276 g of oxygen.

Converting this back to milligrams, we multiply by 1000 to get 127.6 mg of oxygen that was used up during the reaction.