Question

9. For each example, identify whether the
property described is chemical or physical.
Justify your answer in each case.
(a) Bronze metal has a shiny lustre.
(b) When silver nitrate is added to calcium
chloride, a cloudy solid (precipitate)
appears.
(c) Mercury is liquid at room temperature.

Answer 1

To identify whether the properties described are chemical or physical, it's essential to understand the distinction between the two:

- **Physical properties** are characteristics that can be observed or measured without changing the substance's chemical identity. They involve changes in state, appearance, or other physical attributes.
- **Chemical properties** involve the substance's ability to undergo changes that transform it into different substances. These are associated with chemical reactions and changes in composition.

Now, let's analyze each example:

(a) **Bronze metal has a shiny lustre.**
- **Property:** Physical
- **Justification:** The shiny lustre of bronze is a characteristic of its surface appearance. It can be observed without changing the substance itself. This property relates to the way light interacts with the surface of the metal, and it does not involve any chemical change.

(b) **When silver nitrate is added to calcium chloride, a cloudy solid (precipitate) appears.**
- **Property:** Chemical
- **Justification:** The formation of a cloudy solid (precipitate) indicates a chemical reaction between silver nitrate and calcium chloride, resulting in the creation of a new substance (the precipitate). This property reflects a change in chemical composition, distinguishing it as a chemical property.

(c) **Mercury is liquid at room temperature.**
- **Property:** Physical
- **Justification:** The fact that mercury is liquid at room temperature is a physical property related to its state of matter. This can be observed without changing the substance, and it reflects the physical characteristics of mercury rather than its ability to undergo a chemical change.

In summary:
(a) Physical - shiny lustre
(b) Chemical - formation of precipitate
(c) Physical - liquid state at room temperature