Which best describes a compound such as sodium chloride? a) a pure substance that can be separated into different elements by physical means b) a mixture of two common substances that can be separated by chemical means c) a mixture of two common elements that can be separated by physical means d) a pure substance that can be separated into different elements by chemical means.
The correct answer and explanation is:
The correct answer is:
d) a pure substance that can be separated into different elements by chemical means.
Explanation:
Sodium chloride (NaCl) is a classic example of a compound, which means it is a pure substance made up of two or more elements chemically bonded together. In this case, sodium chloride consists of sodium (Na) and chlorine (Cl) atoms bonded in a fixed ratio of 1:1.
- Pure substance:
Sodium chloride is considered a pure substance because it has a uniform and definite composition throughout. Every sample of sodium chloride contains sodium and chlorine atoms combined in the same proportion and structure. - Compound vs. mixture:
A compound is different from a mixture. Mixtures contain two or more substances physically combined, and the components can usually be separated by physical means (like filtration or distillation). Sodium chloride is not a mixture; it’s a compound, where atoms are chemically bonded. - Separation by chemical means:
The elements in sodium chloride are chemically bonded, meaning you cannot separate sodium from chlorine by simple physical processes. Instead, breaking sodium chloride into its elements requires chemical reactions such as electrolysis, where electrical energy breaks the ionic bonds between sodium and chlorine ions. - Why other options are incorrect:
- Option a says sodium chloride can be separated into elements by physical means, which is false because physical means (like filtration or evaporation) do not break chemical bonds.
- Option b suggests sodium chloride is a mixture of two substances, which is incorrect; it is a compound, not a mixture.
- Option c says it is a mixture of elements separable by physical means, which is also incorrect for the same reasons.
In summary, sodium chloride is a pure compound formed by a chemical combination of sodium and chlorine, and separating it into its elements requires chemical methods, making option d the best description.