Final answer:
Jodi should measure the mass of the reactants, including charcoal and oxygen, before starting the combustion reaction to comply with the Law of Conservation of Mass. The initial mass is used for comparison with the mass of the products, ensuring that no matter is lost, only transformed.
Step-by-step explanation:
To test the Law of Conservation of Mass by burning a sample of charcoal, Jodi should measure the mass of the reactants before starting the reaction. This includes weighing the charcoal and the oxygen that will react with it. According to the law, the total mass before the reaction (charcoal + oxygen) must equal the total mass of the products (carbon dioxide, water vapor, and ash) after the reaction. This law suggests that the matter is neither created nor destroyed, only transformed. When charcoal burns in oxygen, it may appear that mass is lost because the products, carbon dioxide and water vapor, may not be visible as they are released into the atmosphere. However, if Jodi were able to capture and measure all the products, she would find that the mass remains constant.
It is important for Jodi to measure the mass when the charcoal and oxygen are contained and before combustion occurs in order to have an accurate initial value for comparison with the mass of the products after the reaction.