Salt analysis

Salt analysis means finding the one anion (acid radical) and the one cation (basic radical) in an inorganic salt you are given. You work in a fixed order: preliminary tests, anion tests, cation group tests, then a confirmatory test for each ion. In the CBSE Class 12 practical exam it is worth 8 of the 30 marks (CBSE Curriculum 2026-27).

This guide follows Unit 7 of the NCERT Laboratory Manual Chemistry Class XII (NCERT Lab Manual XII, Unit 7). Where your school's method differs, follow your teacher.

Quick answers

• Order: preliminary tests (colour, smell, dry heating, flame test, borax bead), anions (dil. H₂SO₄ group, conc. H₂SO₄ group, sulphate and phosphate), cations (group zero to VI), confirmatory tests.
• Group reagents: zero: none (NaOH test for NH₄⁺); I: dil. HCl; II: H₂S in dil. HCl; III: NH₄OH with NH₄Cl; IV: H₂S with NH₄OH; V: (NH₄)₂CO₃ with NH₄OH; VI: none (Na₂HPO₄ test for Mg²⁺).
• The key rule: test the groups in order and stop at the first group that gives a precipitate.
• Marks (CBSE Class 12): salt analysis 8 marks; class record and viva 4 marks, out of 30.

Which ions are in the CBSE syllabus

CBSE 2026-27 Class 12 practical K is "Determination of one anion and one cation in a given salt", insoluble salts excluded (CBSE Curriculum 2026-27):

• Cations: Pb²⁺, Cu²⁺, Al³⁺, Fe³⁺, Mn²⁺, Ni²⁺, Zn²⁺, Co²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Mg²⁺, NH₄⁺
• Anions: CO₃²⁻, S²⁻, SO₃²⁻, NO₃⁻, NO₂⁻, Cl⁻, Br⁻, I⁻, SO₄²⁻, PO₄³⁻, CH₃COO⁻, C₂O₄²⁻

Aim

To detect one cation and one anion in the given salt.

Apparatus and reagents

Boiling tubes, test tubes, a measuring cylinder, a test tube stand and holder, a delivery tube, corks and filter paper, as NCERT lists them. You also need a platinum wire, a watch glass, a burner, lime water, a glass rod, a wash bottle of distilled water, and H₂S (NCERT makes the gas in a Kipp's apparatus). The reagents are named in each test below.

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Theory

A precipitate forms when the ionic product of a salt exceeds its solubility product (K_sp). The ionic product is controlled by the common ion effect: a shift in equilibrium when you add a substance that supplies an ion already present (NCERT Chemistry Class XI, Unit 6). Each group reagent sets conditions where only that group's ions exceed their K_sp, which is called selective precipitation (LibreTexts, Separation of cations in groups).

Procedure: preliminary tests

NCERT says these tests are not conclusive, but they give clues and take about 10 to 15 minutes.

Physical examination

A white salt means these ions are probably absent. A smell of ammonia hints at NH₄⁺; vinegar hints at acetate.

Dry heating test

Heat about 0.1 g of dry salt in a dry test tube for a minute. Note the colour hot and cold.

Flame test

Clean the platinum loop in conc. HCl and a non-luminous flame until it gives no colour. Dip it in a paste of the salt in 2 to 3 drops of conc. HCl and hold it in the flame. HCl is used because metal chlorides are volatile.

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Borax bead test

Only for coloured salts. Make a clear, colourless borax bead on the hot platinum loop, touch it to a little salt and heat again. In the oxidising flame: Cu²⁺ green hot, blue cold; Mn²⁺ light violet; Fe³⁺ yellowish brown hot, yellow cold; Ni²⁺ violet hot, reddish brown cold.

Procedure: anion analysis

Step I: dilute H₂SO₄ group

Take 0.1 g of salt in a test tube and add 1 to 2 mL of dilute H₂SO₄. Watch in the cold, then warm.

Step II: concentrated H₂SO₄ group

If Step I is negative, warm 0.1 g of salt with 3 to 4 drops of conc. H₂SO₄.

Step III: sulphate and phosphate

If Steps I and II are negative, test the water extract for SO₄²⁻ (BaCl₂) and PO₄³⁻ (ammonium molybdate). For a water-insoluble salt NCERT uses a sodium carbonate extract: 1 g salt boiled with 3 g Na₂CO₃ in 15 mL water for 10 minutes, then filtered.

Confirmatory tests for anions

Brown ring test: to 1 mL of salt solution add 2 mL of conc. H₂SO₄ slowly, mix and cool under the tap. Pour freshly prepared FeSO₄ solution slowly down the side of the tube without shaking.

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Anion equations

• Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂
• Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (milky); CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂ (clears)
• Na₂S + H₂SO₄ → Na₂SO₄ + H₂S; (CH₃COO)₂Pb + H₂S → PbS + 2CH₃COOH
• Na₂SO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂
• K₂Cr₂O₇ + H₂SO₄ + 3SO₂ → K₂SO₄ + Cr₂(SO₄)₃ (green) + H₂O
• NaCl + H₂SO₄ → NaHSO₄ + HCl; HCl + NH₃ → NH₄Cl (white fumes)
• NaCl + AgNO₃ → AgCl + NaNO₃; AgCl + 2NH₄OH → [Ag(NH₃)₂]Cl + 2H₂O
• NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃; 4HNO₃ → 4NO₂ + O₂ + 2H₂O
• 6FeSO₄ + 3H₂SO₄ + 2HNO₃ → 3Fe₂(SO₄)₃ + 4H₂O + 2NO; FeSO₄ + NO → [Fe(NO)]SO₄ (brown ring)
• (COONa)₂ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂ + CO
• CaCl₂ + Na₂C₂O₄ → CaC₂O₄ + 2NaCl
• Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Procedure: cation analysis

Original solution (O.S.)

Make a clear solution of the salt. Try each solvent in order, hot if needed, and move on only if the salt does not dissolve: water, dil. HCl, conc. HCl, dil. HNO₃, then aqua regia (conc. HCl and conc. HNO₃, 3:1).

Group zero: NH₄⁺

Heat 0.1 g of salt with 1 to 2 mL of NaOH. A smell of ammonia and white fumes with a rod dipped in HCl show NH₄⁺.

Groups I to VI

(As³⁺ is in the NCERT table but not in the CBSE cation list.)

The group separation logic

1. Add dil. HCl to the O.S. A white precipitate means group I (PbCl₂). If none, go on.
2. Pass H₂S through the same acidified solution. A precipitate means group II. Black means Cu²⁺ or Pb²⁺.
3. If none, take fresh O.S. NCERT heats it with 2 to 3 drops of conc. HNO₃ to oxidise any Fe²⁺ to Fe³⁺. Cool, add solid NH₄Cl, then excess NH₄OH. Reddish brown precipitate is Fe³⁺; gelatinous white is Al³⁺.
4. If none, pass H₂S through that ammoniacal solution. White means Zn²⁺, flesh coloured (buff) means Mn²⁺, black means Ni²⁺ or Co²⁺.
5. If none, take fresh O.S., add NH₄Cl, excess NH₄OH, then (NH₄)₂CO₃. A white precipitate means group V.
6. If none, test for Mg²⁺.

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Lead is listed in both groups I and II. PbCl₂ dissolves in hot water, so some Pb²⁺ can stay in solution and come down later as black PbS.

The conditions decide what precipitates. In group II the acid keeps S²⁻ low, so only sulphides with very low K_sp (CuS, PbS) come down; in group IV the ammonia raises S²⁻ enough for ZnS and MnS (LibreTexts). In group III, NH₄⁺ from NH₄Cl suppresses the ionisation of NH₄OH, so only the least soluble hydroxides, Fe(OH)₃ and Al(OH)₃, precipitate.

Confirmatory tests for cations

NCERT runs these on the group precipitate, dissolved as directed.

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Cation equations

• (NH₄)₂SO₄ + 2NaOH → Na₂SO₄ + 2NH₃ + 2H₂O; NH₃ + HCl → NH₄Cl
• Pb(NO₃)₂ + 2HCl → PbCl₂ + 2HNO₃; PbCl₂ + 2KI → PbI₂ + 2KCl; PbCl₂ + K₂CrO₄ → PbCrO₄ + 2KCl
• CuSO₄ + H₂S → CuS + H₂SO₄; Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ (deep blue)
• 2CuSO₄ + K₄[Fe(CN)₆] → Cu₂[Fe(CN)₆] + 2K₂SO₄
• FeCl₃ + 3NH₄OH → Fe(OH)₃ + 3NH₄Cl; 4FeCl₃ + 3K₄[Fe(CN)₆] → Fe₄[Fe(CN)₆]₃ + 12KCl; Fe³⁺ + SCN⁻ → [Fe(SCN)]²⁺
• AlCl₃ + 3NaOH → Al(OH)₃ + 3NaCl; Al(OH)₃ + NaOH → NaAlO₂ + 2H₂O
• ZnCl₂ + 2NaOH → Zn(OH)₂ + 2NaCl; Zn(OH)₂ + 2NaOH → Na₂ZnO₂ + 2H₂O; 2ZnCl₂ + K₄[Fe(CN)₆] → Zn₂[Fe(CN)₆] + 4KCl
• MnCl₂ + 2NaOH → Mn(OH)₂ + 2NaCl; Mn(OH)₂ + [O] → MnO(OH)₂ (brown)
• BaCO₃ + 2CH₃COOH → (CH₃COO)₂Ba + H₂O + CO₂; (CH₃COO)₂Ba + K₂CrO₄ → BaCrO₄ + 2CH₃COOK
• (CH₃COO)₂Sr + (NH₄)₂SO₄ → SrSO₄ + 2CH₃COONH₄
• (CH₃COO)₂Ca + (NH₄)₂C₂O₄ → CaC₂O₄ + 2CH₃COONH₄
• MgSO₄ + Na₂HPO₄ + NH₄OH → Mg(NH₄)PO₄ + Na₂SO₄ + H₂O

Worked example: copper(II) sulphate

Written the way a practical file records it, in the format of the NCERT specimen record.

Aim: To analyse the given salt for one anion and one cation.

Result: The given salt contains Anion: SO₄²⁻ and Cation: Cu²⁺. The salt is CuSO₄.

Groups III to VI were not tested, because the precipitate came in group II.

Precautions and safety

From NCERT's list, plus what these tests need (NCERT Lab Manual XII, Unit 7):

• Wear an apron, eye protection and gloves.
• Read every label; never use an unlabelled reagent.
• Never taste a chemical. To smell a gas, fan the vapour gently towards your nose.
• Never point a test tube at yourself or a neighbour while heating it or adding a reagent.
• Always add acid to water when diluting, never water to acid.
• Use the minimum quantity of each reagent, drop by drop.
• Use H₂S only in a fume cupboard or where your teacher directs. It is poisonous, can kill at high concentrations, and deadens your sense of smell, so its smell is no warning (OSHA, Hydrogen Sulfide Hazards).
• Concentrated H₂SO₄, HCl and HNO₃ are corrosive. Warm conc. H₂SO₄ tests gently.
• Nessler's reagent contains mercury, and lead and barium salts are toxic. Dispose of them as your teacher says, not down the sink.
• Rinse test tubes with distilled water between tests, and clean the platinum wire with conc. HCl before each flame test. Wash your hands when you finish.

Do these tests only in a school laboratory with a teacher present. None of them are safe to try at home.

Common mistakes and how examiners spot them

• Testing every group. Once a group precipitates, stop and confirm. Results for later groups show the examiner you do not know the scheme.
• Writing "white ppt" as if it settles the question. PbCl₂, BaSO₄, AgCl, Al(OH)₃, ZnS, BaCO₃ and MgNH₄PO₄ are all white. The group and the reagent decide what it is.
• Reading milkiness after H₂S as group II. Fe³⁺ oxidises H₂S to sulphur, which looks milky white or pale yellow (2Fe³⁺ + H₂S → 2Fe²⁺ + S + 2H⁺). A group II precipitate is a black sulphide.
• Skipping the acid before BaCl₂. BaCO₃ and BaSO₃ are also white. Acidifying first dissolves them, so only BaSO₄ stays.
• Not boiling off H₂S before group III. If you use the group II solution for group III, leftover H₂S gives S²⁻ once NH₄OH is added, and group IV sulphides come down in group III.
• Adding NaOH all at once. Al(OH)₃ and Zn(OH)₂ dissolve in excess, so you miss the precipitate.
• No confirmatory test. Every ion in your result needs a "confirmed" line in the record.

Salt analysis viva questions

From the NCERT discussion questions at the end of Unit 7.

1. Why is dilute H₂SO₄ preferred over dilute HCl for testing anions? HCl is volatile and adds Cl⁻, so its fumes confuse the tests. H₂SO₄ is not volatile.
2. Can a glass rod replace the platinum wire in the flame test? No. Glass contains sodium, whose golden-yellow flame hides other colours.
3. CO₂ and SO₂ both turn lime water milky. How do you tell them apart? CO₂ is odourless. SO₂ smells of burning sulphur and turns acidified K₂Cr₂O₇ green.
4. What is the brown ring? Nitroso ferrous sulphate, [Fe(NO)]SO₄, formed at the junction of the two layers.
5. Why is NH₄Cl added before NH₄OH in group III? The common ion NH₄⁺ suppresses the ionisation of NH₄OH, keeping OH⁻ low, so only Fe(OH)₃ and Al(OH)₃ precipitate.
6. Why does ZnS not precipitate in group II? H⁺ from HCl suppresses the ionisation of H₂S, so S²⁻ stays too low for ZnS. Only very low K_sp sulphides like CuS precipitate.
7. Why is the O.S. heated with conc. HNO₃ before group III? To oxidise Fe²⁺ to Fe³⁺, which precipitates completely as Fe(OH)₃.
8. Why is AgNO₃ stored in dark bottles? Light decomposes it, depositing silver.
9. What is Nessler's reagent? An alkaline solution of potassium tetraiodomercurate(II), K₂HgI₄.
10. Why are group V ions tested in the order Ba²⁺, Sr²⁺, Ca²⁺? Ba²⁺ also gives white precipitates in the Sr²⁺ and Ca²⁺ tests, so it is ruled out first.

Try it in 3D

You can practise the wet tests on the free salt analysis virtual lab from Student Intelligence. The 3D bench and its controls work without signing in:

• Choose one of 12 salts, or "Salt X", which picks one of them at random and hides its name until you identify it.
• Pick any of 8 test tubes and add the salt, water, the original solution, or any of 20 labelled reagents.
• Heat the tube, hold a glass rod dipped in NH₄OH or HCl at its mouth, and do the flame test on the platinum wire.
• Each addition is worked out from the ions in the tube: precipitate colours, dissolving in excess, effervescence, fumes, the brown ring.
• Turn on See-through to watch the ions meet and form a precipitate. The bench turns all the way round.
• A short quiz and a few flashcards sit on the same page.

The bench covers 11 of the 13 CBSE cations (no Ni²⁺ or Co²⁺) and four anions: CO₃²⁻, Cl⁻, NO₃⁻ and SO₄²⁻. It uses H₂S water instead of H₂S gas from a Kipp's apparatus. The guided experiment, where the tutor walks you through the tests in NCERT's order, needs a free sign-in.

FAQ

What is the difference between a group reagent and a confirmatory test?

A group reagent precipitates a whole group under set conditions, like H₂S in dilute HCl for group II. A confirmatory test then picks out one ion, like the deep blue colour for Cu²⁺.

Why do we prepare an original solution?

The cation wet tests need the ions in solution. Try water first, then the acids in the order given above.

Which salts are given in the CBSE practical exam?

CBSE does not name the salts. It lists the ions and excludes insoluble salts, so expect a soluble salt of one listed cation and one listed anion.

Is salt analysis in Class 11 the same?

Almost. The CBSE 2026-27 Class 11 list (practical F) has the same 13 cations and the same anions, except oxalate (C₂O₄²⁻), which only Class 12 adds. A much shorter list, with NH₄⁺ as the only cation, is for visually challenged students.

Want to run the tests yourself before the exam? Open the free salt analysis lab on Student Intelligence and try Salt X.

Sources

• NCERT. Laboratory Manual Chemistry, Class XII, Unit 7: Systematic Qualitative Analysis (Experiment 7.1, Tables 7.1 to 7.16, flow chart, precautions, discussion questions, specimen record). https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classXII/chemistry/lelm107.pdf
• CBSE. Chemistry (Subject Code 043), Curriculum 2026-27, Classes XI and XII: practical evaluation scheme and qualitative analysis lists for Classes XI and XII. https://cbseacademic.nic.in/web_material/CurriculumMain27/SecPart2/Chemistry_SecP2_2026-27.pdf
• NCERT. Chemistry Part I, Class XI, Unit 6: Equilibrium (6.11.8 Common ion effect; 6.13.2 Common ion effect on solubility). https://ncert.nic.in/textbook/pdf/kech106.pdf
• LibreTexts Chemistry. Qualitative Analysis of Common Cations in Water (Malik), 1.5: Separation of cations in groups. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Qualitative_Analysis_of_Common_Cations_in_Water_%28Malik%29/1%3A_Chemical_Principles/1.5%3A_Separation_of_cations_in_groups
• Occupational Safety and Health Administration (OSHA). Hydrogen Sulfide: Hazards. https://www.osha.gov/hydrogen-sulfide/hazards