8.6 Going Deeper: Enrichment & Exam Preparation

Matter in Everyday Life

Sorting Your Surroundings Your kitchen is a chemistry set: salt and sugar are compounds, gold jewellery is an element, brass handles and steel utensils are mixtures (alloys), the air is a mixture, and the water in your glass is a compound. Once you can spot which is which, the material world clicks into place.

Quick Reference

Type Made of Separated by Example
Element One kind of atom Cannot be broken down Gold, oxygen, iron
Compound Elements chemically joined, fixed ratio Only chemically Water, salt, sugar
Mixture Substances just mixed, own properties kept Physically Air, seawater, brass
Test Mixture Compound
Composition Variable Fixed ratio
Properties Those of components Brand new
Made by Mixing (physical) Chemical change
Separation Physical methods Chemical only

Memory Tricks & One-Page Revision

Revision Card

  • Matter → pure substances (elements, compounds) + mixtures.
  • Element: one kind of atom; can’t be broken down (gold, oxygen).
  • Compound: elements chemically combined in a fixed ratio; new properties (water = H:O = 2:1; salt = Na:Cl = 1:1).
  • Mixture: components keep their properties; no chemical reaction; physically separable. Uniform (air, seawater) or non-uniform (salad, sand+water).
  • Alloys (steel, brass, bronze) are uniform mixtures of metals.
  • Iron + sulfur mixed = mixture (magnet pulls iron out); heated = iron sulfide compound (no magnet effect, rotten-egg gas with acid).
  • Minerals: mostly compounds, a few native elements.
  • Not matter: light, heat, electricity, thoughts.

Spot the Mistake

Find the Flaw

  1. “Air is a compound because it has oxygen and nitrogen joined together.” — False: air is a mixture — the gases aren’t chemically joined and can be separated physically.
  2. “Water has the same properties as hydrogen and oxygen.” — False: a compound’s properties are completely different (water puts out fires!).
  3. “A compound can be separated into its elements by filtering or evaporation.” — False: compounds need a chemical change to break apart, not a physical one.

Test Your Reflexes

A quick-fire drill: a substance appears. Is it an Element, a Compound, or a Mixture? Build a streak!

Element, compound, or mixture?
Classify each substance.
Score 0 · Streak 0

Exam Corner: CBSE-Style Practice

Mixed Practice (objective, short, long, HOTS)

Objective type (1 mark each)

  1. A substance that cannot be broken down into anything simpler is an ______.
  2. In water, hydrogen and oxygen atoms combine in a fixed ratio of ______.
  3. Stainless steel, brass and bronze are examples of ______ (uniform mixtures of metals).

Short answer (2 marks each)

  1. Give two differences between a mixture and a compound.
  2. Why does lime water turn milky when left open to the air?

Long answer (3 marks each)

  1. In Activity 8.5, how can you tell the iron-sulfur mixture apart from the iron sulfide compound? Give the magnet and acid tests.
  2. Classify each as element, compound or mixture: carbon dioxide, aluminium, seawater, sodium chloride, brass, oxygen.

HOTS (Higher Order Thinking)

  1. A + B → C, where A and B cannot be broken down chemically. What are A, B and C, and which has a fixed composition?
  2. Can a substance be both an element and a compound at the same time? Explain.

Assertion–Reason (Choose: (a) both true, R explains A; (b) both true, R doesn’t explain A; (c) A true, R false; (d) A false, R true.)

  1. Assertion (A): Water has very different properties from hydrogen and oxygen.   Reason (R): In a compound, the elements combine chemically to form a new substance.
  1. element.
  2. 2 : 1 (hydrogen : oxygen).
  3. alloys.
  4. (Any two) A mixture has variable composition; a compound has a fixed ratio. A mixture keeps its components’ properties and can be separated physically; a compound has new properties and needs a chemical change to separate.
  5. The carbon dioxide in the air reacts with the calcium hydroxide in lime water to form insoluble white calcium carbonate, which makes it look milky.
  6. Magnet test: a magnet pulls the iron out of the mixture (Sample A) but has no effect on iron sulfide (Sample B). Acid test: the mixture gives odourless hydrogen (“pop”); iron sulfide gives hydrogen sulfide (rotten-egg smell). So A is a mixture, B is a compound.
  7. Elements: aluminium, oxygen. Compounds: carbon dioxide, sodium chloride. Mixtures: seawater, brass.
  8. A and B are elements (can’t be broken down); C is a compound formed from them, and C has a fixed composition.
  9. No. An element is made of one kind of atom and cannot be broken down; a compound is two or more elements chemically joined. A substance is one or the other, never both.
  10. (a) — Both true and R explains A: chemical combination forms a new substance, so the compound’s properties differ from its elements’.

Glossary

Key Terms

  • Mixture: two or more substances mixed, keeping their properties; no chemical reaction.
  • Uniform / non-uniform mixture: evenly distributed (invisible components) vs visibly separate.
  • Alloy: a uniform mixture of metals (steel, brass, bronze).
  • Pure substance: matter of a single kind of particle; an element or a compound.
  • Element: the simplest substance; made of one kind of atom; can’t be broken down.
  • Compound: elements chemically combined in a fixed ratio, with new properties.
  • Mineral: a natural solid of fixed composition; usually a compound, sometimes a native element.