Mini Chemistry
Part of Mini EducationSwitch subject

Qualitative Analysis Notes

Learn and apply Qualitative Analysis Notes in the published Chemistry course sequence.

  • GCE A-Level H2 Chemistry 9476-2027
On this page

Using the Qualitative Analysis Notes: Orientation

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.
What the exam supplies

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.

Detailed Explanations

A. Workflow: writing a full QA answer

  1. Name the reagent and how it is added (dropwise / in excess / warm).
  2. State the observation (colour/precipitate/gas).
  3. 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.

Paper 4 reality check

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).

Worked Examples

Modelled example 1

Use Two Supplied-Note Columns to Identify Chloride

Core

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

  1. 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).

  2. 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

About 6 min

Problem

Dilute acid added to a solid produces a gas that turns limewater milky. Deduce the gas and the anion supported by the supplied-note context.

Try this before viewing the solution

Direct gas-test observation
Gas inference
Anion inference

Hints

Hint 1: observation first
Write what happens to limewater before naming the gas.
Hint 2: source ion
Then use the acid–anion reaction specified by the candidate set.
View solution step by step

  1. 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).

  2. 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

Find and correct the mistake

Learner answer

A question asks for the result of adding aqueous sodium hydroxide to an iron(III) solution. A learner writes only “Fe³⁺ is present.” Explain what is missing and write a complete response.

Try this before viewing the solution

Missing observation
In excess NaOH

View solution step by step

  1. 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.

  2. 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

4 marks

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

  1. Interpret gas A

    1 mark

    Method

    Identify chlorine from bleaching damp litmus paper.

    Reason

    The prescribed positive observation matches chlorine.

    Working

    Gas A: Cl₂(g).

  2. Interpret gas B

    1 mark

    Method

    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).

  3. State the assessment boundary

    2 marks

    Method

    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.

Challenge 5

Combine Cation and Anion Evidence from Fresh Portions

Minimal support

QA synthesis

One portion of an unknown solution releases a gas on warming with aqueous sodium hydroxide; the gas turns damp red litmus blue. A fresh portion, acidified with dilute nitric acid, gives a white precipitate with silver nitrate. Identify the cation and anion.

Try this before viewing the solution

Cation
Anion

Hints

Hint 1: first portion
Use the damp-litmus observation to identify the gas, then its source cation.
Hint 2: fresh portion
Use silver-halide colour only after checking the acid did not introduce a halide.
View solution step by step

  1. 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).

  2. 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).

  3. 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.

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.