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Principles Related to Practical Chemistry · Question 25

AIPMT 2011 (Prelims)MCQEasy📈 Topic in 38% papers+4−1
1

The Lassaigne's extract is boiled with conc. HNO3 while testing for halogens. By doing so it

  1. decomposes Na2S and NaCN, formed
  2. helps in the precipitation of AgCl
  3. increases the solubility product of AgCl
  4. increases the concentration of NO3- ions

Answer

(1) decomposes Na2S and NaCN, formed

Solution

As per NCERT, if nitrogen or sulphur is also present in the compound, the sodium fusion extract is first boiled with concentrated nitric acid to decompose cyanide or sulphide of sodium formed during sodium fusion.

NaCN + HNO3 NaNO3 + HCN

Na2S + 2HNO3 2NaNO3 + H2S

These ions would otherwise give precipitates with AgNO3 and interfere with the test for halogens.

Answer: (1)

AIPMT 2011 (Prelims)

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2

In Dumas method of estimation of nitrogen, 0.35 g of an organic compound gave 55 mL of nitrogen collected at 300 K temperature and 715 mm pressure. The percentage composition of nitrogen in the compound would be (aqueous tension at 300 K = 15 mm).

  1. 15.45
  2. 16.45
  3. 17.45
  4. 14.45
Out of syllabusAIPMT 2011 (Prelims)
3

The best method for the separation of naphthalene and benzoic acid from their mixture is

  1. distillation
  2. sublimation
  3. chromatography
  4. crystallisation.
AIPMT 2005
4

Which of the following is incorrect?

  1. FeCl3 is used in detection of phenol.
  2. Fehling's solution is used in detection of glucose.
  3. Tollens' reagent is used in detection of unsaturation.
  4. NaHSO3 is used in detection of carbonyl compound.
AIPMT 2001
5

In steam distillation of toluene, the pressure of toluene in vapour is

  1. equal to pressure of barometer
  2. less than pressure of barometer
  3. equal to vapour pressure of toluene in simple distillation
  4. more than vapour pressure of toluene in simple distillation.
AIPMT 2001

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