HESI A20
HESI A2 Chemistry Practice Test
1. A molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass. This is a statement of _____.
- A. The law of multiple proportions
- B. The law of conservation of mass
- C. The law of conservation of energy
- D. The law of constant composition
Correct answer: D
Rationale: The statement that a molecule of water contains hydrogen and oxygen in a 1:8 ratio by mass is an example of the law of constant composition. This law states that all samples of a given chemical compound have the same elemental composition. In the case of water (H2O), no matter where you obtain a sample of water, it will always be composed of hydrogen and oxygen in a 1:8 ratio by mass. The law of multiple proportions deals with compounds that can be formed by the combination of elements in different ratios. The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted.