Mixture vs Compound: Heat Effect MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz covers the Practicals (Unit I) topic of mixtures versus compounds. It focuses on the heating observations of iron filings and sulphur powder, distinct properties, and separation methods. Complete the 10 questions below and submit to download your PDF solution key.
Understanding Mixtures vs Compounds: Heating Iron and Sulphur
In this practical, students observe the differences between a physical mixture of iron filings and sulphur powder compared to the chemical compound formed when they are heated together (Iron(II) sulfide). The experiment demonstrates how chemical properties change during a chemical reaction.
1. Properties of the Mixture (Before Heating)
When iron filings (grey) and sulphur powder (yellow) are mixed without heating, they retain their individual properties:
- Appearance: Heterogeneous; distinct grey and yellow particles are visible.
- Magnetic Separation: Iron filings can be separated using a magnet.
- Solubility in Carbon Disulphide (CS2): Sulphur dissolves in CS2, leaving iron behind.
- Reaction with Acid (HCl): Iron reacts to release Hydrogen gas (H2), which burns with a “pop” sound. Sulphur remains unreacted.
2. Properties of the Compound (After Heating)
When the mixture is strongly heated, a chemical reaction occurs to form Iron(II) sulphide (FeS). The properties change completely:
- Appearance: A hard, black, homogenous mass.
- Magnetic Separation: A magnet has no effect; iron has lost its magnetic property in the compound.
- Solubility in CS2: Neither iron nor sulphur dissolves.
- Reaction with Acid (HCl): The compound reacts to release Hydrogen Sulphide (H2S) gas, which smells like rotten eggs.
Key Differences Table
| Property | Mixture (Fe + S) | Compound (FeS) |
|---|---|---|
| Magnet Effect | Separates Iron | No separation |
| Solvent (CS2) Effect | Dissolves Sulphur | No effect |
| Gas with Dil. HCl | Hydrogen (Pop sound) | H2S (Rotten egg smell) |
| Heat Action | No new substance | Black mass formed |
Quick Revision Notes
- Heating the mixture is an exothermic process; the reaction continues even after removing the flame due to heat evolution.
- The ratio of iron to sulphur is fixed by mass in the compound (FeS) but variable in the mixture.
- Safety Note: H2S gas is toxic; avoid inhaling it directly. CS2 is highly flammable; keep away from flames.
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