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Unit 8: Chemical reactions

GRADE 6 – Unit 8: Chemical reactions — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 9 parts Lesson 1 of 13 1 quiz

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

GRADE 6 - Unit 8: Chemical reactions — HIA INTERNATIONAL notes: Distinguish chemical reactions from physical changes, detect reactions, test gases and describe neutralisation.Physical change — no new substance forms, so the change can usually be reversed.Chemical reaction — new s…

  • Reactants and products
  • Word equation
  • Conservation of mass
  • Metals and acid
  • Carbon dioxide
  • Testable question

Section 1 of 9Physical changes and chemical reactions

Physical change
  • Physical change no new substance forms, so the change can usually be reversed.
Chemical reaction
  • Chemical reaction new substances form and the change is usually hard to reverse.
Reactants and products
  • Reactants and products reactants are the starting substances and products are the new ones.
Word equation
  • Word equation shows reactants then products, for example magnesium + oxygen gives magnesium oxide.
Conservation of mass
  • Conservation of mass atoms are rearranged, not created or destroyed, so total mass stays the same.

Section 2 of 9Signs of a chemical reaction

ClueWhat you seeExample
Gas given offBubbles or fizzingMagnesium with hydrochloric acid
Colour changeNew colourBlack copper oxide with sulfuric acid gives blue copper sulfate
Heat producedTemperature risesZinc with hydrochloric acid
Reactant disappearsSolid is used upMagnesium ribbon in acid
PrecipitateA solid forms in a liquidSilver nitrate with calcium chloride gives silver chloride
pH changepH moves towards 7Neutralisation of an alkali

Section 3 of 9Burning and metals

Burning
  • Burning a substance reacts with oxygen to form an oxide.
Magnesium
  • Magnesium burns to form white magnesium oxide.
Carbon
  • Carbon burns to form carbon dioxide.
Rusting
  • Rusting iron reacts with oxygen and water to form rust, and both are needed.
Metals and acid
  • Metals and acid a metal reacts with an acid to give a salt and hydrogen.

Section 4 of 9Tests for gases

GasTestPositive result
HydrogenLit splintSqueaky pop
OxygenGlowing splintRelights
Carbon dioxideBubble through limewaterLimewater turns cloudy
  • Limewater
    • a solution of calcium hydroxide that forms a precipitate of calcium carbonate with carbon dioxide.

Section 5 of 9Preparing gases

Carbon dioxide
  • Carbon dioxide calcium carbonate with hydrochloric acid, or baking powder with vinegar.
Oxygen
  • Oxygen hydrogen peroxide with manganese dioxide or with apple, which contains chemicals that make it react.
Hydrogen
  • Hydrogen metal such as magnesium or zinc with hydrochloric acid.

Section 6 of 9Neutralisation

Neutralisation
Neutralisation acid and alkali reacting to give a neutral solution of pH 7.
Word equation
  • Word equation hydrochloric acid + sodium hydroxide gives sodium chloride + water.
Burette
  • Burette adds acid slowly to an alkali with universal indicator until green.
Uses
  • Uses antacids for indigestion, toothpaste, adding alkali to acid lakes and lime on acidic soil.

Section 7 of 9Investigating acids and alkalis

Testable question
  • Testable question it must be precise so that an experiment can answer it.
Fair test
  • Fair test change one variable, measure one variable and keep the others the same.
Reliability
  • Reliability repeat the test and calculate a mean, leaving out anomalous results.
Safety
  • Safety wear safety glasses and follow hazard warnings.

Section 8 of 9Key terms

TermMeaning
Chemical reactionA change that forms new substances.
ReactantA substance that takes part in a reaction.
ProductA new substance formed in a reaction.
PrecipitateAn insoluble solid formed when solutions react.
NeutralisationThe reaction of an acid with an alkali to give a neutral solution.
LimewaterA solution of calcium hydroxide used to test for carbon dioxide.
VariableSomething that can change in an investigation.
OxideA compound of an element with oxygen.

Section 9 of 9Exam technique

1
Thinking a physical change makes a new substance — melting and freezing are physical changes.
2
Saying bubbles always mean hydrogen — each gas must be tested.
3
Saying the mass changes in a closed reaction — mass is conserved.
4
Thinking fizzing means a strong acid — it shows a gas is made.
5
Forgetting rusting needs both oxygen and water.

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