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2hInorganic Chemistry

Chemical tests — Edexcel Modular - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 8 of 8 1 quiz

📚 Edexcel Modular - OL (Chemistry) Hub / Topical Revision
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Lesson summary

Chemical tests Edexcel O Level Modular Chemistry notes: describe tests for these gases: - hydrogen - oxygen - carbon dioxide - ammonia - chlorine.Gases can be compressed because particles are far apart.Gas pressure increases with temperature.Air is a mixture of gases, not a compo…

  • Chemical tests Edexcel O Level Modular Chemistry: what to do next
  • Give / State / Name
  • Evaluate / Assess
  • Keywords the mark scheme looks for in this lesson
  • How to get full marks (examiner guidance)
  • Link ideas

Section 1 of 7Process & sequence

1
Note the colour of the solution first.
2
Add the reagent named in the question.
3
Record exactly what you see, including any precipitate colour.
4
Test in excess reagent if the question asks.
5
Name the ion from the observations.
  • Observe first
  • Add reagent
  • Record observation
  • Name the ion

Section 2 of 7Keep going

Chemical tests Edexcel O Level Modular Chemistry: what to do next

These Chemical tests Edexcel O Level Modular Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Chemical tests Edexcel O Level Modular Chemistry understanding with the practice questions below, then reread any Chemical tests Edexcel O Level Modular Chemistry point you were unsure about before moving on.

1
Practice: Chemical tests Edexcel O Level Modular Chemistry practice questions
2
Previous lesson: 2g Acids, bases and salt preparations — Notes
3
Next lesson: 3a Energetics — Notes
4
Course: Edexcel Modular – OL (chemistry) — all units
5
Official syllabus: Pearson Edexcel International GCSEs

Chemical tests Edexcel O Level Modular Chemistry revision notes

Section 3 of 7Compare

Properties and tests of gases
GasFormula% in airTestPositive resultUse
OxygenO₂21%Glowing splintRelightsBreathing, hospitals, welding
Carbon dioxideCO₂0.04%Bubble through limewaterLimewater turns milkyFire extinguishers, fizzy drinks
HydrogenH₂TraceLighted splintSqueaky popFuel, balloons (old)
NitrogenN₂78%—Puts out flameFood packaging
ChlorineCl₂NoneDamp litmus paperBleached whiteCleaning water
HeliumHeTrace——Balloons, airships

Section 4 of 7Key terms

Section 5 of 7Syllabus checklist

1
describe tests for these gases: - hydrogen - oxygen - carbon dioxide - ammonia - chlorine.
2
describe how to carry out a flame test
3
know the colours formed in flame tests for these cations:
  • Li+ is red
  • Na+ is yellow
  • K+ is lilac
  • Ca2+ is orange-red
  • Cu2+ is blue-green
4
describe tests for these cations:
  • NH4+ using sodium hydroxide solution and identifying the gas evolved
  • Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution
5
describe tests for these anions:
  • Cl−, Br− and I− using acidified silver nitrate solution
  • SO42− using acidified barium chloride solution
  • CO32− using hydrochloric acid and identifying the gas evolved
6
describe a test for the presence of water using anhydrous copper(II) sulfate
7
describe a physical test to show whether a sample of water is pure

Section 6 of 7Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Section 7 of 7Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Gas · Oxygen · Carbon dioxide · Hydrogen · Nitrogen · Density · Diffusion · Test
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

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