Why is understanding density important when identifying unknown substances?

• A. Because density changes with the color of a substance.
• B. Because density determines the chemical reactivity of a substance.
• C. Because density is the only property needed to identify any substance.
• D. Because density is a unique physical property that can help distinguish one substance from another.

Answer: (D)

Verified step by step guidance

1. Understand that density is defined as the mass of a substance divided by its volume, expressed as \(\text{density} = \frac{\text{mass}}{\text{volume}}\).
2. Recognize that density is a physical property, meaning it does not change regardless of the amount of substance present, making it useful for identification.
3. Know that different substances have characteristic densities, so measuring the density of an unknown sample can help narrow down what the substance might be.
4. Realize that density is unique to each substance under specific conditions (temperature and pressure), so it can serve as a fingerprint to distinguish substances.
5. Note that while density is helpful, it is not the only property used for identification, but it is a reliable and straightforward physical property to measure.