Which one of the following laws explains the formation of both carbon monoxide and carbon dioxide from carbon and oxygen?

Introduction / Context:
Early chemists observed regular patterns in the way elements combine. These observations led to several fundamental laws of chemical combination. The existence of more than one compound formed by the same elements, such as carbon monoxide (CO) and carbon dioxide (CO2), is explained by one specific law. This question tests your knowledge of which law deals with such pairs of compounds.

Given Data / Assumptions:

• The elements involved are carbon and oxygen.
• The compounds considered are carbon monoxide (CO) and carbon dioxide (CO2).
• We must choose among several laws of chemical combination and Avogadro law.
• We assume a basic school level understanding of these laws.

Concept / Approach:
The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole number ratios. For carbon monoxide and carbon dioxide, the mass of oxygen that combines with a fixed mass of carbon is in a simple ratio of 1:2. The law of conservation of mass deals with total mass before and after reaction, the law of definite proportions covers constant composition of a single compound, the law of reciprocal proportions relates combining weights of three elements, and Avogadro law relates volume and number of moles of a gas.

Step-by-Step Solution:
Step 1: Consider carbon monoxide (CO), where one atom of carbon combines with one atom of oxygen. Step 2: Consider carbon dioxide (CO2), where one atom of carbon combines with two atoms of oxygen. Step 3: For a fixed mass of carbon, the mass of oxygen in CO is proportional to one oxygen atom, and in CO2 it is proportional to two oxygen atoms. Step 4: The ratio of masses of oxygen that combine with a fixed mass of carbon in the two compounds is therefore 1:2, a simple whole number ratio. Step 5: This observation matches directly the statement of the law of multiple proportions. Step 6: Hence, the formation of carbon monoxide and carbon dioxide from carbon and oxygen is explained by the law of multiple proportions.

Verification / Alternative check:
Textbooks usually illustrate the law of multiple proportions using examples like carbon monoxide and carbon dioxide or different oxides of nitrogen. In each case, comparing the mass of one element that combines with a fixed mass of the other shows simple whole number ratios. For CO and CO2, experimental data confirm that the mass of oxygen per unit mass of carbon follows a 1:2 ratio. Other laws of combination do not focus on multiple compounds of the same two elements, which confirms that the correct law here is the law of multiple proportions.

Why Other Options Are Wrong:
Law of conservation of mass: States that total mass remains constant in a chemical reaction, but does not specifically address multiple compounds of the same elements.
Law of reciprocal proportions: Deals with three elements and how they combine with each other, not with two compounds of the same pair of elements.
Law of definite proportions: Explains that a given compound has a fixed composition, but does not compare two different compounds of the same elements.
Avogadro law: Relates gas volume to number of moles at constant temperature and pressure, and does not concern mass ratios in compound formation.

Common Pitfalls:
Some students confuse the law of definite proportions with the law of multiple proportions because both involve ratios and composition. The key difference is that the law of definite proportions applies to one compound, while the law of multiple proportions compares two or more compounds formed by the same elements. Remember that the words multiple proportions themselves hint at more than one compound, which fits the situation with carbon monoxide and carbon dioxide.

Final Answer:
The formation of carbon monoxide and carbon dioxide from carbon and oxygen is explained by the law of multiple proportions.