Answer to Question #26769 in Chemistry for Gertrude Holztler

Question

In an experiment to determine the percentage composition of an oxide, the element is allowed to burn in air and the oxide formed is collected. Describe how we can determine the mass of the oxygen in the air that was reacted.

Answer 1

Burning of an element in air can be described by a reaction:

El + O₂ = ElO₂

The amount of moles of each participant of the reaction describes by a ratio:

n = m/M
where m - mass, grams
M - molar mass, grams/mole.
So, knowing the mass and a molar mass of an element, we can calculate the amount of moles. The moles ratio in a reaction is being described by coefficients. By the coefficient ratio of the reaction members we can calculate the needed amount of O₂:
m = nM