Which of the following does not illustrate the law of multiple proportions?
A. H₂O₂ and H₂O
B. CO₂ and CO
C. Na₂O and Na₂O₂
D. H₂O and D₂O
Answer (2)
Option D: H₂O and D₂O does not illustrate the law of multiple proportions because both compounds consist of the same elements in the same ratio despite the difference in isotopes. In contrast, the other options show different compounds that maintain the ratio of elements required by the law. Therefore, D is the best choice for this question.
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The law of multiple proportions is a fundamental principle in chemistry, formulated by John Dalton in the early 19th century. It 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 a ratio of small whole numbers.
Let's analyze each of the given options to determine which one does not illustrate the law of multiple proportions:
A. H₂O₂ and H₂O - Both are compounds of hydrogen and oxygen. In water (H₂O), the ratio of hydrogen to oxygen by mass is approximately 2:16, while in hydrogen peroxide (H₂O₂), it is approximately 2:32. The ratio of the masses of oxygen that combine with a fixed mass of hydrogen is 16:32 or 1:2, which is a simple whole number ratio. This does illustrate the law of multiple proportions.
B. CO₂ and CO - Both are compounds of carbon and oxygen. In carbon dioxide (CO₂), the ratio of oxygen to carbon by mass is approximately 32:12, while in carbon monoxide (CO), it is 16:12. The ratio of the masses of oxygen that combine with a fixed mass of carbon in CO₂ to CO is 32:16 or 2:1, which is a whole number ratio. This also illustrates the law of multiple proportions.
C. Na₂O and Na₂O₂ - These are compounds of sodium and oxygen. In sodium oxide (Na₂O), the ratio of the mass of sodium to oxygen is approximately 46:16, while in sodium peroxide (Na₂O₂), it is 46:32. The ratio of the masses of oxygen that combine with a fixed mass of sodium is 16:32 or 1:2, which is a simple whole number ratio. This illustrates the law of multiple proportions.
D. H₂O and D₂O - These represent water molecules where hydrogen (H) is replaced by deuterium (D), an isotope of hydrogen. The compounds have identical compositions in terms of chemical formula since deuterium is simply a heavier isotope of hydrogen, not a different element. As a result, there is no difference in mass ratios of different elements but only isotopic variation. This does not represent the law of multiple proportions, as the law requires different compounds formed by two elements, not isotopes of the same element.
The correct choice that does not illustrate the law of multiple proportions is D. H₂O and D₂O .
