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Qualitative analysis of the officially listed cations and anions: NEET MCQs with answers

50 questions on this topic of Principles Related to Practical Chemistry (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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1. A white salt dissolves in water to give a neutral solution. Addition of dilute H₂SO₄ gives no reaction. Addition of BaCl₂ solution gives a white precipitate which is insoluble in concentrated HNO₃. When the original solution is tested with neutral FeCl₃ solution, it gives no reaction. The anion present is:

  1. SO₃²⁻
  2. SO₄²⁻
  3. CO₃²⁻
  4. PO₄³⁻
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Answer: (B) SO₄²⁻

Barium sulphate (BaSO₄) is a white precipitate that is insoluble in concentrated mineral acids including conc. HNO₃ and conc. HCl. Sulphite precipitate (BaSO₃) dissolves in mineral acids with the evolution of SO₂.

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2. When an aqueous solution of manganese(II) cation is oxidized by boiling with lead dioxide (PbO₂) and concentrated HNO₃, the supernatant solution turns purple-pink. This is due to the formation of:

  1. Mn₂O₇
  2. HMnO₄
  3. Mn(NO₃)₂
  4. Pb(MnO₄)₂
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Answer: (B) HMnO₄

Mn²⁺ is oxidized by PbO₂ in the presence of concentrated HNO₃ to permanganic acid (HMnO₄ or MnO₄⁻), which imparts a characteristic purple/pink colour: 2Mn²⁺ + 5PbO₂ + 4H⁺ → 2MnO₄⁻ + 5Pb²⁺ + 2H₂O.

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3. An aqueous solution of a metal ion 'M' gives a white precipitate with potassium ferrocyanide, K₄[Fe(CN)₆], which turns bluish-white on addition of excess reagent. The metal ion 'M' is:

  1. Fe²⁺
  2. Zn²⁺
  3. Cu²⁺
  4. Ca²⁺
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Answer: (B) Zn²⁺

Zn²⁺ reacts with potassium ferrocyanide to form a white or bluish-white precipitate of zinc ferrocyanide or potassium zinc ferrocyanide, K₂Zn₃[Fe(CN)₆]₂. Fe²⁺ gives a light blue precipitate which turns dark blue on exposure to air.

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4. In the confirmatory test for barium ions (Ba²⁺), the addition of potassium chromate (K₂CrO₄) solution produces a yellow precipitate that is:

  1. insoluble in both dilute HCl and acetic acid
  2. insoluble in dilute acetic acid but soluble in dilute HCl
  3. soluble in dilute acetic acid but insoluble in dilute HCl
  4. soluble in both dilute acetic acid and dilute HCl
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Answer: (B) insoluble in dilute acetic acid but soluble in dilute HCl

Ba²⁺ forms yellow BaCrO₄ upon reaction with K₂CrO₄. Barium chromate is insoluble in dilute acetic acid, which distinguishes Ba²⁺ from Sr²⁺ and Ca²⁺, but it dissolves readily in dilute mineral acids such as HCl.

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5. Consider the following two statements regarding the qualitative detection of anions: Statement I: A salt of sulfite (SO₃²⁻) reacts with dilute H₂SO₄ to evolve SO₂ gas, which turns acidified K₂Cr₂O₇ paper green. Statement II: The green colour produced on the paper is due to the formation of chromium(III) sulfate [Cr₂(SO₄)₃]. In the light of the above statements, choose the correct option:

  1. Both Statement I and Statement II are true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Statement I is false but Statement II is true
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Answer: (A) Both Statement I and Statement II are true

Sulfite salts react with dilute mineral acids to liberate SO₂ gas. SO₂ reduces orange acidified dichromate (Cr₂O₇²⁻) to green chromium(III) ion according to: K₂Cr₂O₇ + H₂SO₄ + 3SO₂ → K₂SO₄ + Cr₂(SO₄)₃ + H₂O.

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6. In Group V cation analysis, a mixture containing Ba²⁺, Sr²⁺, and Ca²⁺ is precipitated as carbonates. After dissolving the carbonates in dilute acetic acid, Ba²⁺ is separated using K₂CrO₄. To the remaining filtrate, which sequence of reagents confirms the presence of Sr²⁺ and Ca²⁺ respectively?

  1. Addition of (NH₄)₂SO₄ precipitates SrSO₄; addition of (NH₄)₂C₂O₄ to the remaining solution precipitates CaC₂O₄
  2. Addition of NaOH precipitates Ca(OH)₂; addition of H₂S precipitates SrS
  3. Addition of (NH₄)₂C₂O₄ precipitates SrC₂O₄; addition of KI precipitates CaI₂
  4. Addition of NH₄OH precipitates Sr(OH)₂; addition of K₂CrO₄ precipitates CaCrO₄
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Answer: (A) Addition of (NH₄)₂SO₄ precipitates SrSO₄; addition of (NH₄)₂C₂O₄ to the remaining solution precipitates CaC₂O₄

After removing barium as yellow BaCrO₄, the solution contains Sr²⁺ and Ca²⁺. Addition of ammonium sulfate [(NH₄)₂SO₄] precipitates Sr²⁺ as white SrSO₄ while CaSO₄ remains largely in solution. In the remaining filtrate, Ca²⁺ is confirmed by adding ammonium oxalate [(NH₄)₂C₂O₄], which yields white calcium oxalate (CaC₂O₄).

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7. Given below are two statements: Statement I: Carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻) can be distinguished by adding magnesium sulphate (MgSO₄) solution to their cold aqueous solutions. Statement II: Magnesium carbonate precipitates in the cold, whereas magnesium bicarbonate precipitates only upon boiling. In light of the above statements, choose the correct answer:

  1. Both Statement I and Statement II are true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Statement I is false but Statement II is true
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Answer: (A) Both Statement I and Statement II are true

Magnesium sulphate produces a white precipitate of MgCO₃ with cold soluble carbonate solutions. With soluble bicarbonates, Mg(HCO₃)₂ remains soluble in cold water and only precipitates as MgCO₃ upon heating or boiling.

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8. When a solid chloride salt is treated with concentrated H₂SO₄, colourless fumes of HCl are evolved. Which of the following cations forms a chloride that does NOT respond to the chromyl chloride test?

  1. Ca²⁺
  2. Pb²⁺
  3. Zn²⁺
  4. Ba²⁺
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Answer: (B) Pb²⁺

Chlorides of heavy metals with high covalent character like Pb²⁺, Hg²⁺, Ag⁺, and Sn²⁺ do not produce sufficient free chloride ions to form chromyl chloride vapor (CrO₂Cl₂). Therefore, PbCl₂ does not respond to the chromyl chloride test.

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9. In the confirmatory test for calcium ions (Ca²⁺), the addition of ammonium oxalate, (NH₄)₂C₂O₄, in an ammoniacal medium gives a white precipitate. This precipitate is soluble in:

  1. Dilute acetic acid
  2. Cold water
  3. Ammonium hydroxide solution
  4. Dilute hydrochloric acid
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Answer: (D) Dilute hydrochloric acid

Calcium oxalate (CaC₂O₄) is insoluble in dilute acetic acid and ammonium hydroxide, but dissolves readily in dilute mineral acids such as dilute HCl or dilute HNO₃ because oxalate is the conjugate base of a weak acid (oxalic acid).

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10. A mixture containing Cu²⁺ and Ni²⁺ is to be separated during qualitative inorganic analysis. Which reagent selectively precipitates Cu²⁺ leaving Ni²⁺ in solution?

  1. Ammonium carbonate in presence of NH₄Cl
  2. H₂S in ammoniacal medium (NH₄OH + NH₄Cl)
  3. H₂S in acidic medium (dilute HCl)
  4. Ammonium phosphate in presence of NH₄OH
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Answer: (C) H₂S in acidic medium (dilute HCl)

Cu²⁺ belongs to Group II and has a very low solubility product (Ksp) for its sulphide, precipitating as CuS in the presence of dilute HCl. In contrast, Ni²⁺ belongs to Group IV, having a higher Ksp for its sulphide, so it remains in solution in an acidic medium.

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11. In the brown ring test for the nitrate ion (NO₃⁻), a freshly prepared solution of FeSO₄ is added to the salt solution followed by the gentle addition of concentrated H₂SO₄ along the sides of the test tube. What is the oxidation state of iron and the magnetic nature of the brown complex [Fe(H₂O)₅(NO)]SO₄ formed at the junction?

  1. +1, paramagnetic with three unpaired electrons
  2. +2, paramagnetic with four unpaired electrons
  3. +1, diamagnetic
  4. +3, paramagnetic with five unpaired electrons
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Answer: (A) +1, paramagnetic with three unpaired electrons

In the brown ring complex [Fe(H₂O)₅(NO)]²⁺, nitric oxide acts as a neutral or positively charged ligand transferring an electron to iron, resulting in Fe in the +1 oxidation state (3d⁷). With weak-field ligands (H₂O and NO⁺), it adopts a high-spin configuration with 3 unpaired electrons, making it paramagnetic.

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12. During the group separation of cations, concentrated HNO₃ is added before the addition of NH₄Cl and NH₄OH in Group III. What is the essential chemical function of this addition?

  1. To dissolve any unprecipitated Group II sulphides
  2. To convert Fe²⁺ to Fe³⁺ because Fe(OH)₂ is not completely precipitated by NH₄OH
  3. To increase the concentration of OH⁻ ions via nitric acid decomposition
  4. To prevent the precipitation of Al³⁺ as its basic nitrate
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Answer: (B) To convert Fe²⁺ to Fe³⁺ because Fe(OH)₂ is not completely precipitated by NH₄OH

Iron may exist as Fe²⁺ in solution following H₂S reduction in Group II. Ferrous hydroxide Fe(OH)₂ has a significantly higher solubility product than Fe(OH)₃ and does not precipitate completely with NH₄OH in the presence of NH₄Cl; hence conc. HNO₃ is boiled to oxidize Fe²⁺ to Fe³⁺.

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