JEE Chemistry Organic Chemistry Some Basic Principles and Techniques MCQs Set 71

Answer: (c) Na₄[Fe(CN)₅NOS]

Explanation:
1. Sulphur is converted to Na₂S in the extract.
2. Na₂S combines with nitroprusside to give the violet sodium thionitroprusside, Na₄[Fe(CN)₅NOS].
3. Answer: (c)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (d) A catalyst

Explanation:
1. Nitrogen is converted to (NH₄)₂SO₄ on digestion with conc. H₂SO₄.
2. CuSO₄ speeds up this digestion as a catalyst, and K₂SO₄ raises the boiling point.
3. Answer: (d)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (d) Convert the covalent compound into a mixture of ionic compounds

Explanation:
1. Fusion with sodium converts N, S and halogens into NaCN, Na₂S and NaX.
2. These are ionic and dissolve in water, so they can be tested by ordinary ionic tests.
3. Answer: (d)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (d) Sodium bicarbonate

Explanation:
1. The carboxylic acid is stronger than carbonic acid, so it dissolves in NaHCO₃ as its sodium salt with evolution of CO₂.
2. A phenol is weaker than carbonic acid and stays undissolved.
3. NaOH would dissolve both.
4. Answer: (d)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (b) Beilstein's test

Explanation:
1. In Beilstein's test an organic compound on a copper wire loop is heated in a flame.
2. Volatile copper halides give a green or blue-green flame.
3. Answer: (b)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (a) 73.29%

Explanation:
1. % C = (12/44) × (0.147/0.2) × 100 = 20.05.
2. % H = (2/18) × (0.12/0.2) × 100 = 6.67.
3. % O = 100 − 20.05 − 6.67 = 73.29.
4. Answer: (a)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (b) Na₂S and NaCN are decomposed by HNO₃

Explanation:
1. Na₂S and NaCN would otherwise give black Ag₂S and white AgCN with AgNO₃.
2. Boiling with HNO₃ expels H₂S and HCN, so only the silver halides precipitate.
3. Answer: (b)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (b) Steam distillation

Explanation:
1. Aniline is volatile in steam and immiscible with water, and it decomposes if distilled alone at its boiling point.
2. Steam distillation therefore separates it from non-volatile impurities.
3. Answer: (b)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (a) 26.32%

Explanation:
1. Milliequivalents of NH₃ = 20 × 0.5 = 10, i.e. 10 millimoles of N.
2. Mass of N = 10 × 14 mg = 0.14 g.
3. Percentage = 0.14 / 0.532 × 100 = 26.32.
4. Answer: (a)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (b) 93.5

Explanation:
1. The salt is (BH)₂PtCl₆, so its molar mass = 0.75 × 195 / 0.245 = 597.
2. The PtCl₆ part weighs 195 + 213 = 408.
3. 2(B + 1) = 597 − 408 = 189, so B = 93.5.
4. Answer: (b)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.

Answer: (b) FeCl₃

Explanation:
1. Thiocyanate forms the blood-red [Fe(SCN)]²⁺ complex with Fe³⁺ ions.
2. Fe²⁺ (FeSO₄) does not give this colour.
3. Answer: (b)

Teacher's Note:
1. Recall what each reagent or step does in the detection or estimation of elements in organic compounds.