Qualitative Analysis Notes
Use the supplied qualitative-analysis tables to draw conclusions from a sequence of tests.
On this page
Qualitative Analysis (QA) marks come from writing observations clearly and then making a justified inference. Most mark loss happens when students write the ion name with no observation.
Use this with Paper 4 Skills: Planning, MMO, PDO, ACE and the Practical and QA (A Level) hub so method, data, and evaluation marks stay aligned.
When to use this page
- Night before Paper 4 to refresh core QA wording.
- During timed practice when you keep losing marks for vague observations.
- Right before checking your practical answer script for missing inference steps.
The official Qualitative Analysis Notes are included in the Paper 4 question paper. Other books and laboratory notebooks are not permitted. Learn how to navigate the tables and interpret evidence; do not spend revision time reproducing every row from memory.
Definitions (Must Know)
A. Observation
An observation is what you see (colour change, precipitate colour, gas produced).
B. Inference
An inference is the conclusion you draw from observations (which ion/gas is present).
C. “In excess”
In excess means enough reagent has been added that some remains after reaction (used to test whether a precipitate dissolves).
D. Acidify
To acidify means add a dilute acid first (as instructed) to remove interfering ions before adding the test reagent.
Key Ideas (What Earns Marks)
- Write: reagent added → observation → inference (in that order).
- Use examiner words: “forms a precipitate”, “dissolves in excess”, “effervescence”, “pungent gas”.
- If a gas forms, name the gas and give the confirmatory test + observation.
- If the protocol says “acidify”, state the acid used and then add the test reagent.
Detailed Explanations
A. Workflow: writing a full QA answer
- Name the reagent and how it is added (dropwise / in excess / warm).
- State the observation (colour/precipitate/gas).
- State the inference (ion/gas).
Mini example (halide test):
- Add dilute HNO₃(aq), then add AgNO₃(aq). A white precipitate forms. The anion is Cl⁻.
Because marks are awarded for the observation, therefore you should never write only “Cl⁻ present” with no precipitate/colour statement.
The 9476 carry-out exclusions are specific: hexane, sulfur dioxide gas, nitrite ions, sulfite ions, 2,4-DNPH, phosphorus(V) chloride and phenol. Results from the supplied notes may still need to be interpreted.
B. Quick reminders (high-frequency mark points)
- Acidify before AgNO₃(aq) (halides) and before Ba²⁺ (sulfate) if the question tells you to.
- Excess NH₃(aq) dissolves Cu(OH)₂(s) to give a deep blue solution (complex formation).
- Fe²⁺ precipitates often darken on standing (oxidation in air).
Practise the reagent, observation and inference sequence on unknown cations, anions and gases, with results from the 9476 Qualitative Analysis Notes.
Unknown 1: a solution of one cation. Nothing tested yet.
- Reagent added to this portion
- 0.00 cm³
- Portions tested
- 0
- Tests done
- 0
- Still possible
- 11
Try this
0 of 4 doneTest an unknown cation until only one ion in the Notes fits. (not done yet)
Some cations need both reagents: Al³⁺ and Zn²⁺ both give a white ppt. that dissolves in excess NaOH(aq), but only Zn(OH)₂ dissolves in excess NH₃(aq).
Test an unknown anion until only one ion in the Notes fits. (not done yet)
Each anion test is specific: a halide precipitates with acidified Ag⁺, sulfate with acidified Ba²⁺, a carbonate fizzes with acid and a nitrate gives ammonia with Al and NaOH(aq).
Identify an unknown gas with the tests for gases. (not done yet)
One test can mislead: SO₂ also turns limewater milky, so CO₂ needs limewater and SO₂ needs acidified potassium manganate(VII).
Add Ba(NO₃)₂(aq) to the carbonate without acidifying it first. (not done yet)
Barium carbonate is also a white ppt., so a carbonate could pass for a sulfate. Acidifying with nitric acid first removes carbonate as CO₂.
Worked Examples
Modelled example 1
Use Two Supplied-Note Columns to Identify Chloride
Problem
After acidification with dilute HNO₃(aq), an unknown gives a white precipitate with AgNO₃(aq). The precipitate dissolves in dilute NH₃(aq) to give a colourless solution. Deduce the anion.
Study the worked solution
Use precipitate colour
Method
Match the white precipitate to silver chloride.Reason
The supplied halide table gives white, pale-cream and yellow for AgCl, AgBr and AgI respectively.
Working
White precipitate supports AgCl(s).
Use ammonia solubility
Method
Confirm chloride because the precipitate dissolves in dilute ammonia.
Reason
Silver chloride is soluble under this supplied-note condition, strengthening the colour inference.
Working
Inference: Cl - aq.
Guided practice 2
Build a Complete Carbonate Evidence Chain
Problem
Try this before viewing the solution
Hints
Hint 1: observation first
Hint 2: source ion
View solution step by step
Separate observation and gas inference
Method
Record effervescence and limewater turning milky, then identify carbon dioxide.Reason
A named gas is an inference; the milky limewater is the confirming observation.Working
Gas: CO₂(g).Infer the anion
Method
State carbonate ions in the supplied-note context.Reason
Carbonate releases carbon dioxide on acidification.Working
Inference: CO₃²⁻; hydrogencarbonate would need to remain a candidate if included by the question.
Common misconception 3
Correct an Inference-Only QA Answer
Learner answer
Try this before viewing the solution
View solution step by step
Restore the evidence
Method
State that aqueous sodium hydroxide added dropwise forms a red-brown precipitate, insoluble in excess.Reason
The observation is the marked experimental result that supports the ion name.Working
Reagent → colour/state → excess behaviour.Make the inference
Method
Then state that the pattern is consistent with Fe³⁺.Reason
The supplied cation table links that full pattern to iron(III).Working
Complete answer: red-brown precipitate, insoluble in excess; Fe³⁺ present.
Examiner practice 4
Interpret Supplied Gas Results Within the 9476 Boundary
Examination question
Supplied observations state that gas A bleaches damp litmus paper and gas B decolourises aqueous acidified potassium manganate(VII). Identify both gases and explain what the supplied notes do—and do not—require a 9476 candidate to do. [4 marks]
Try this before viewing the solution
View solution step by step
Interpret gas A
1 markMethod
Identify chlorine from bleaching damp litmus paper.
Reason
The prescribed positive observation matches chlorine.
Working
Gas A: Cl₂(g).Interpret gas B
1 markMethod
Identify sulfur dioxide from decolourisation of acidified potassium manganate(VII).
Reason
The supplied gas-test table links that observation to sulfur dioxide.
Working
Gas B: SO₂(g).State the assessment boundary
2 marksMethod
Use supplied notes to interpret given evidence, but do not infer that every listed test must be carried out.
Reason
9476 specifically excludes candidates from being required to carry out tests involving sulfur dioxide gas or sulfite ions.
Working
Interpretation is in scope; excluded practical performance is not.
Self-mark with the mark scheme
Compare your response with each mark point. Select a point only when your response contains that evidence.
Self-mark both gas identities and both parts of the supplied-notes boundary.
Challenge 5
Combine Cation and Anion Evidence from Fresh Portions
QA synthesis
Try this before viewing the solution
Hints
Hint 1: first portion
Hint 2: fresh portion
View solution step by step
Infer the cation
Method
Identify ammonia from damp red litmus turning blue, then infer ammonium ions.Reason
Ammonium ions release ammonia on warming with aqueous hydroxide.Working
NH₄ + (aq) + OH-(aq) → NH₃(g) + H₂O(l).Infer the anion
Method
Identify the white precipitate as silver chloride and infer chloride ions.Reason
Nitric acid does not add halide; white is the supplied colour for AgCl(s).Working
Ag + (aq) + Cl-(aq) → AgCl(s).Combine the evidence
Method
Report ammonium and chloride as the ions supported in the unknown.Reason
Fresh portions keep the cation and anion procedures from contaminating each other.Working
Supported solute: ammonium chloride.
Common Mistakes
- Writing inference-only (naming the ion) without giving the observation that earns the mark.
- Forgetting ‘in excess’ outcomes (especially for cations with NaOH/NH₃).
- Naming a gas but omitting the confirmatory test and observation.
Use the Practical and QA topic check to practise and check your understanding.
Exam Tips
- Use the examiner format: reagent + observation + inference. Don’t write inference-only.
- For gases, include the confirmatory test and the key word observation (e.g. ‘limewater turns milky’).
- When results are given, you are tested on interpretation even if the test is ‘not required to carry out’.
Mind Stretchers
Mind stretcher 1Extension
An unknown solution forms a white precipitate when NaOH(aq) is added dropwise. The precipitate dissolves in excess NaOH(aq). When NH₃(aq) is added, a white precipitate forms and dissolves in excess to give a colourless solution. Identify the cation.
Show Hint
List observations first, then eliminate candidates only when the supplied evidence distinguishes them.
Show Answer
Mark scheme:
- Zn²⁺ (white Zn(OH)₂(s) dissolves in excess NaOH(aq) and in excess NH₃(aq)).
Mind stretcher 2: Avoiding an overconfident inferenceExtension
Question. An unknown gives a white precipitate with aqueous sodium hydroxide that dissolves in excess. Explain why this does not identify one cation and name the next supplied-note test needed to distinguish the possibilities.
Show Hint
List observations first, then eliminate candidates only when the supplied evidence distinguishes them.
Show Answer
The result is consistent with Al³⁺ or Zn²⁺ (and Cr³⁺ is excluded by its grey-green precipitate). Test a fresh portion with aqueous ammonia: Zn²⁺ gives a white precipitate soluble in excess, whereas Al³⁺ gives a white precipitate insoluble in excess. The inference should remain non-unique until that evidence is obtained.
Syllabus and review details
- GCE A-Level H2 Chemistry 9476-2027 · 9476-2027
9476 (2027), complete syllabus
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