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Surface Chemistry · Question 23

AIPMT 2004MCQEasy📈 Topic in 25% papers+4−1
1

Which of the following forms cationic micelles above certain concentration?

  1. Sodium dodecyl sulphate
  2. Sodium acetate
  3. Urea
  4. Cetyltrimethylammonium bromide.

Answer

(4) Cetyltrimethylammonium bromide.

Solution

As per NCERT, micelles are formed by surface active agents above the critical micelle concentration (CMC); the long hydrophobic chains point inwards and the ionic heads face the water.

⇒ For a cationic micelle, the long chain must carry a positive head: cetyltrimethylammonium bromide, CH3(CH2)15N+(CH3)3Br-, is a cationic detergent.

∵ Sodium dodecyl sulphate gives anionic micelles; sodium acetate and urea have no long hydrophobic chain and form no micelles.

∴ Cetyltrimethylammonium bromide forms cationic micelles.

Answer: (4)

Out of syllabusAIPMT 2004

Keep practising — Surface Chemistry

2

According to the adsorption theory of catalysis, the speed of the reaction increases because

  1. the concentration of reactant molecules at the active centres of the catalyst becomes high due to adsorption
  2. in the process of adsorption, the activation energy of the molecules becomes large
  3. adsorption produces heat which increases the speed of the reaction
  4. adsorption lowers the activation energy of the reaction.
Out of syllabusAIPMT 2003
3

Position of non-polar and polar part in micelle

  1. polar at outer surface but non-polar at inner surface
  2. polar at inner surface but non-polar at outer surface
  3. distributed over all the surface
  4. are present in the surface only
Out of syllabusAIPMT 2002
4

Which is not correct regarding the adsorption of a gas on surface of a solid?

  1. On increasing temperature adsorption increases continuously.
  2. Enthalpy and entropy change is negative.
  3. Adsorption is more for some specific substance.
  4. It is a reversible reaction.
Out of syllabusAIPMT 2001
5

Which one of the following methods is commonly used for the destruction of a colloid?

  1. Dialysis
  2. Condensation
  3. Filtration by animal membrane
  4. By adding electrolyte
Out of syllabusAIPMT 2000

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