Principles Related to Practical Chemistry

10 NEET-UG practice questions on Principles Related to Practical Chemistry, part of Chemistry. The first 10 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   Neutral FeCl₃ solution produces a violet colour with which of these compounds?

   1. ABenzaldehyde
   2. BPhenol
   3. CBenzyl alcohol
   4. DAniline

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   Answer: B · Phenol

   Phenols form a coloured iron(III) complex with neutral ferric chloride, which is the standard functional group test for the phenolic -OH.

   • A: This has no phenolic -OH and is tested with Tollens' or 2,4-DNP reagent.
   • C: The -OH here is alcoholic, attached to a side-chain carbon, not to the ring.
   • D: This is an amine, tested by the carbylamine or azo dye test.

   Remember this

   A violet colour with neutral FeCl₃ indicates a phenolic -OH; an alcoholic -OH does not respond.

2. Question 2 · Easy

   When oxalic acid is titrated against KMnO₄ in dilute H₂SO₄, what indicates the end point?

   1. AStarch, by a blue colour
   2. BKMnO₄ itself, by a lasting pink colour
   3. CMethyl orange, by a red colour
   4. DPhenolphthalein, by a pink colour

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   Answer: B · KMnO₄ itself, by a lasting pink colour

   MnO₄⁻ is intensely purple and Mn²⁺ is almost colourless. The first slight excess of KMnO₄ therefore leaves a lasting pink colour, so no added indicator is needed.

   • A: Starch is the indicator for iodine titrations.
   • C: Methyl orange is also an acid-base indicator.
   • D: Phenolphthalein is an acid-base indicator, and this is a redox titration.

   Remember this

   KMnO₄ is a self-indicator in acidic medium titrations.

3. Question 3 · Medium

   A salt solution is mixed with freshly prepared FeSO₄ solution, and conc. H₂SO₄ is poured slowly down the side of the test tube. A brown ring forms. Which species causes the colour?

   1. A[Fe(CN)₅(NO)]²⁻
   2. B[Fe(H₂O)₅(NO₂)]²⁺
   3. C[Fe(H₂O)₅(NO)]²⁺
   4. D[Fe(H₂O)₆]³⁺

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   Answer: C · [Fe(H₂O)₅(NO)]²⁺

   Nitrate is reduced by Fe²⁺ in acid to NO, which then binds to a further Fe²⁺ to replace one water ligand. This confirms nitrate in the salt.

   • A: This is the nitroprusside ion, which has cyanide ligands not present here.
   • B: This has a nitro ligand, while the reduction product is NO.
   • D: This is a simple hexaaqua ion, which contains no nitrosyl ligand.

   Remember this

   The brown ring test confirms NO₃⁻; the colour comes from the nitrosyl complex [Fe(H₂O)₅(NO)]²⁺.

4. Question 4 · Hard

   Given below are two statements: Statement I: Before adding AgNO₃ to test for halogen, the sodium fusion extract is boiled with conc. HNO₃ to decompose any sodium cyanide and sodium sulphide. Statement II: Hydrazine does not give the Lassaigne test for nitrogen because it has no carbon to form NaCN. Choose the correct answer.

   1. AStatement I is incorrect but Statement II is correct
   2. BStatement I is correct but Statement II is incorrect
   3. CBoth Statement I and Statement II are correct
   4. DBoth Statement I and Statement II are incorrect

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   Answer: C · Both Statement I and Statement II are correct

   Cyanide and sulphide would also precipitate with Ag⁺ and give a false result, so boiling with nitric acid removes them first. The nitrogen test depends on NaCN forming during fusion, which needs carbon as well as nitrogen, and hydrazine has no carbon.

   • A: Statement I is right, since cyanide and sulphide would interfere with AgNO₃.
   • B: Statement II is right, since no NaCN can form without carbon.
   • D: Both statements are right, so neither can be rejected.

   Remember this

   Lassaigne's nitrogen test needs NaCN, so both C and N must be present; nitric acid removes interfering ions before the halogen test.

5. Question 5 · Medium

   Arrange these group reagents in the order in which they are used in the systematic analysis of cations. A. (NH₄)₂CO₃ in NH₄OH B. Dilute HCl C. NH₄OH with NH₄Cl D. H₂S in dilute HCl

   1. AD, B, C, A
   2. BB, D, C, A
   3. CB, C, D, A
   4. DB, D, A, C

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   Answer: B · B, D, C, A

   Dilute HCl precipitates group I chlorides first. H₂S in acid brings down group II sulphides, NH₄OH with NH₄Cl brings down group III hydroxides, and (NH₄)₂CO₃ later brings down group V carbonates.

   • A: This uses H₂S first, which would also precipitate lead and other group I ions as sulphides.
   • C: This brings ammonia in before acidic H₂S, which would mix group II ions with the later groups.
   • D: This uses carbonate before group III, which would precipitate group III along with it.

   Remember this

   Group reagents in order: dilute HCl, H₂S in acid, NH₄OH with NH₄Cl, H₂S in NH₄OH, then (NH₄)₂CO₃.

6. Question 6 · Medium

   In a Carius determination, 0.20 g of an organic compound gave 0.188 g of AgBr. What is the percentage of bromine in the compound? (Ag = 108, Br = 80)

   1. A20%
   2. B94%
   3. C40%
   4. D54%

   Answer and explanation in LearnFree account

7. Question 7 · Easy

   What volume of 0.1 M NaOH neutralises 20 mL of 0.1 M oxalic acid?

   1. A80 mL
   2. B20 mL
   3. C10 mL
   4. D40 mL

   Answer and explanation in LearnFree account

8. Question 8 · Medium

   Why is a little dilute H₂SO₄ added to the water while preparing crystals of Mohr's salt?

   1. ATo prevent hydrolysis of the ferrous ions
   2. BTo precipitate ammonium sulphate
   3. CTo remove the water of crystallisation
   4. DTo oxidise Fe²⁺ to Fe³⁺

   Answer and explanation in LearnFree account

9. Question 9 · Medium

   Match List-I with List-II. List-I (Cation) A. Pb²⁺ B. Cu²⁺ C. Fe³⁺ D. NH₄⁺ List-II (Confirmatory observation) I. Brown precipitate with Nessler's reagent II. Yellow precipitate with KI III. Deep blue solution with excess NH₄OH IV. Blue colour with K₄[Fe(CN)₆]

   1. AA-I, B-III, C-IV, D-II
   2. BA-II, B-III, C-IV, D-I
   3. CA-III, B-II, C-IV, D-I
   4. DA-II, B-IV, C-III, D-I

   Answer and explanation in LearnFree account

10. Question 10 · Hard

    Mohr's salt, FeSO₄·(NH₄)₂SO₄·6H₂O (M = 392 g/mol), weighing 3.92 g is made up to 100 mL. A 20 mL portion is titrated with 0.02 M KMnO₄ in dilute H₂SO₄. What volume of KMnO₄ is used?

    1. A100 mL
    2. B40 mL
    3. C20 mL
    4. D4 mL

    Answer and explanation in LearnFree account