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11.4Unit 8: Chemical reactions

Detecting chemical reactions — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 7 parts Lesson 4 of 4 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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Lesson summary

11.4 Detecting chemical reactions — CHECKPOINT (CHEMISTRY) notes: Identify evidence for chemical reactions and test for hydrogen, carbon dioxide and oxygen.ClueExampleA gas is given offMagnesium and hydrochloric acid give hydrogen bubblesA reactant disappearsMagnesium ribbon is u…

  • Precipitate
  • Silver chloride
  • Risk assessment
  • Heating copper sulfate solution
  • Potassium and water
  • Glowing splint

Section 1 of 7Clues that a reaction has happened

ClueExample
A gas is given offMagnesium and hydrochloric acid give hydrogen bubbles
A reactant disappearsMagnesium ribbon is used up in acid
Colour changeBlack copper oxide and sulfuric acid give blue copper sulfate
Heat is producedZinc with hydrochloric acid warms the tube
pH changesNeutralisation of an alkali by an acid
A precipitate formsSilver nitrate and calcium chloride give solid silver chloride

Section 2 of 7Tests for gases

GasTestResult
HydrogenLighted splint at the mouth of the tubeSqueaky pop
Carbon dioxideBubble through limewaterLimewater turns cloudy
OxygenGlowing splint in the tubeSplint relights

Section 3 of 7Examples of gas-producing reactions

Hydrogen
  • Hydrogen magnesium + hydrochloric acid → magnesium chloride + hydrogen
Carbon dioxide
  • Carbon dioxide baking powder and vinegar, or calcium carbonate and hydrochloric acid
Oxygen
  • Oxygen hydrogen peroxide with apple or manganese dioxide

Section 4 of 7Precipitates

Precipitate
Precipitate a solid formed when two solutions react
Silver chloride
  • Silver chloride silver nitrate + calcium chloride → silver chloride + calcium nitrate
Limewater
  • Limewater calcium hydroxide + carbon dioxide → calcium carbonate + water
  • The solid calcium carbonate makes limewater cloudy.

Section 5 of 7Safety

Safety
Risk assessment
  • Risk assessment carry one out before any reaction
Heating copper sulfate solution
  • Heating copper sulfate solution do not boil it as harmful fumes are given off
Potassium and water
  • Potassium and water teacher demonstration only

Section 6 of 7Key terms

TermMeaning
PrecipitateSolid formed when two solutions react.
LimewaterCalcium hydroxide solution that turns cloudy with carbon dioxide.
Glowing splintSplint with a glowing end used to test for oxygen.
Squeaky popResult of the hydrogen test.
EffervescenceFizzing as a gas is made.

Section 7 of 7Exam technique

1
Saying bubbles always mean hydrogen — each gas needs its own test.
2
Putting the splint inside the tube for the hydrogen test instead of at the mouth.
3
Saying a colour change is not a reaction clue.
4
Confusing a precipitate with a solution.

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