Final answer:
The proportion by mass of carbon to oxygen in the carbon dioxide you exhale is the same as in any sample of carbon dioxide due to the Law of Multiple Proportions, always having a mass ratio of 2.66 grams of oxygen to 1 gram of carbon.
Step-by-step explanation:
The Law of Multiple Proportions states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in the ratio of small whole numbers. For carbon dioxide (CO2), if you have 24 grams of carbon, there would be 2.666 grams of oxygen for every gram of carbon, resulting in 64 grams of oxygen.
In carbon monoxide (CO), if the compound contains 2.666 grams of oxygen, there would be twice the mass of carbon, which equates to 12 grams of carbon. The proportion by mass of carbon to oxygen in the carbon dioxide you exhale is the same as in any sample of carbon dioxide because of the constant composition of compounds.
The mass ratio in CO2 will always be 2.66 grams of oxygen for every 1 gram of carbon.