Question

Which of the following is NOT a property of a pure substance?

1. Heterogeneous in chemical aggregation
2. Homogenous in chemical aggregation
3. Homogenous in composition
4. Invariable in chemical aggregation 

Answer 1

Correct Answer - Option 1 : Heterogeneous in chemical aggregation

Explanation:

Pure substance - 

• A pure substance is one that is uniform and invariable in chemical composition.
• A pure substance can exist in more than one phase, but its chemical composition must be the same in each phase.

Examples of Pure substances :

• liquid water and water vapor form a system with two phases, the system can be regarded as a pure substance because each phase has the same
• composition implies a Homogeneous composition.  
• A uniform mixture of gases can be regarded as a pure substance provided it remains a gas and doesn’t react chemically.
• Air can be regarded as a pure substance as long as it is a mixture of gases because it is Homogeneous in chemical aggregate
• If the mixture of gases forms a liquid phase on cooling, the liquid would have a different composition than the gas phase, and becomes Heterogeneous in chemical composition and the system would no longer be considered a pure substance.​