Mixture vs Compound: Appearance MCQs Quiz | Class 9

This Class IX Science (Code 086) quiz covers Unit I: Practicals, specifically focusing on the topic of Mixtures versus Compounds. The questions explore key distinctions such as homogeneity vs heterogeneity, visual appearance, and physical properties. Test your understanding of how to distinguish between a physical mixture and a chemical compound, then click Submit to see your score and download the detailed PDF answer sheet.

Understanding Mixtures and Compounds

In Class 9 Science, distinguishing between mixtures and compounds is a fundamental concept in the “Matter Around Us Is Pure” chapter and related practicals. A key aspect of this distinction is the visual appearance and the uniformity of the substance.

1. Homogeneity vs. Heterogeneity

The primary visual difference often lies in uniformity:

  • Homogeneous: The substance has a uniform composition throughout. You cannot see the separate boundaries of the constituents. Compounds (like pure water) and true solutions (like sugar in water) are homogeneous.
  • Heterogeneous: The substance has non-uniform composition. You can often see the distinct particles or layers. Mixtures can be heterogeneous (like sand and iron filings) or homogeneous (like alloys), but most simple mechanical mixtures are heterogeneous.

2. Key Differences Table

Feature Mixture Compound
Composition Variable ratio of constituents Fixed ratio by mass
Properties Constituents retain their original properties Properties are entirely different from constituents
Separation Can be separated by physical methods (magnet, filtration) Can only be separated by chemical or electrochemical methods
Melting Point Variable, no sharp melting point Fixed, sharp melting point
Formation Physical change (no new substance) Chemical change (new substance formed)

3. Iron and Sulfur Experiment

A classic practical involves iron filings and sulfur powder:

  • Mixture: Greyish-yellow powder. Iron retains magnetic properties (attracted to magnet). Sulfur dissolves in carbon disulfide.
  • Compound (Iron Sulfide): Black solid obtained after heating. Non-magnetic. Neither constituent retains its original properties.

Quick Revision Points

  • Compounds always have a definite formula (e.g., H2O, FeS).
  • Mixtures do not have a specific chemical formula.
  • Formation of a compound usually involves absorption or release of energy (heat/light).
  • Formation of a mixture involves little to no energy exchange.

Extra Practice Questions

1. If a substance melts at a sharp, specific temperature, is it likely a mixture or a compound?
Answer: Compound.

2. Air is considered a mixture. Why?
Answer: Its composition varies slightly by location and its components (N2, O2) retain their properties.

3. Is brass a compound?
Answer: No, brass is an alloy, which is a homogeneous mixture of copper and zinc.

4. When water boils, does it become a new compound?
Answer: No, it undergoes a physical change from liquid to gas, remaining H2O.

5. Can you separate salt from water using filtration?
Answer: No, salt water is a homogeneous mixture; evaporation or distillation is required.