Solubility: Solvation and association in solutions and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam

SOLVATION:

The interaction between solute and solvent molecule which leads to stabilisation of solute species in the solution is called as solvation.

The strength and nature of interaction between the solute molecule and solvent influences many properties of solute like stability, colour, reactivity and in case of solvent properties like density, viscosity are affected.

In the process of solvation an ion in a solution is surrounded or complexed by solvent molecules.

The Interaction between solute and solvent results in formation of different forces or bonds like :–

1. Attractive or repulsive forces
2. Vander wall forces
3. Hydrogen bonding
4. Ion dipole interaction

Solvation is a kinetic process and is quantified by its rate. Solvation of solute with water is called hydration.

Association:

It is a chemical reaction where by ions of opposite electrical change come together in solution to form a distinct chemical entity.

The forces involved in the attraction of opposite electric charge are electrostatic force.

Ion associate have been characterized by means of vibration spectroscopy. The most important factor to determine the extent of ion association is dielectric constant of the solvent.

Ion association are classified according to the number of ion that associate with each other such as

(A)ion pairs, (B) ion triplets etc.

(A)Ion pairs: Ion pairs are formed when a cation and anion come together.

A_n+ + B_m- ↔ AB(n-m)^–₊

Types of ionpair :

1. Fully solvent
2. Solvent shared or Solvent separated
3. Contact ion pair.

1) Fully Solvent ion pair :—

When both ions have a complete primary solvation sphere then the ion pair is known as fully solvated ion pair.

2) Solvent shared:—-

When there is about one solvent molecule between the cation and anion then the ion pair is called as solvent shared or solvent separated ion pair.

3) Contact ion pair :—-

When the ions are in contact with each other the ion pair is termed as Contact ion pair .

(B)Ion triplet: The association constant of 3 ions is called as ion triplet.

Multiple choice questions(MCQs)

1.The concentration of a solution is defined as

a)The amount of solvent present in a given amount of solution

b)The amount of solute present in a given amount of solution

c)The amount of solute present in a given amount of solvent

d)The amount of solvent present in a given amount of solute

2.The interaction between solute and solvent molecule which leads to stabilization of solute species in the solution is called as 

a)association

b)solvation

c)both of these

d)none of these

3.The strength and nature of interaction between the solute molecule and solvent influences many properties of solute like

a)stability

b)colour

c)reactivity

d)all of the above

4.When a saturated solution prepared at a higher temperature is cooled, we get

a)Super cooled solution

b)Super saturated solution

c)An equilibrium mixture

d)One molar solution

5.The Interaction between solute and solvent results in formation of different forces or bonds like

a)Attractive or repulsive forces

b)Vander wall forces

c)Hydrogen bonding

d)all of the above

6.Solvation is a

a)kinetic process

b)static process

c)dynamic process

d)all of the above

7.Solvation of solute with water is called

a)hydrotrophy

b)hydration

c)deliquiscency

d)efflorescency

8.It is a chemical reaction where by ions of opposite electrical change come together in solution to form a distinct chemical entity.

a)solvation

b)association

c)both of these

d)none of these

9.The forces involved in the attraction of opposite electric charge are

a)electrostatic forces

b)Vander wall forces

c)Hydrogen bonding

d)all of the above

10.Ion associate have been characterized by means of 

a)chromatography

b)vibration spectroscopy

c)colorimetry

d)potentiometry

11.The most important factor to determine the extent of ion association is

a)dielectric constant

b)pH

c)partition coefficient

d)normality

12.Ion association are classified according to the number of ion that associate with each other such as

a)ion pairs

b)ion triplets

c)ionic pairs

d)a) and b)

13.Which of the following are types of ion pair?

a)Fully solvent

b)Solvent shared or Solvent separated

c)Contact ion pair

d)all of the above

14.When both ions have a complete primary solvation sphere then the ion pair is known as 

a)Fully solvent

b)Solvent shared or Solvent separated

c)Contact ion pair

d)all of the above

15.The association constant of 3 ions is called as 

a)Fully solvent

b)Solvent shared or Solvent separated

c)Contact ion pair

d)ion triplet

Solutions:

1. b)The amount of solute present in a given amount of solution
2. c)both of these
3. d)all of the above
4. b)Super saturated solution
5. d)all of the above
6. a)kinetic process
7. b)hydration
8. b)association
9. a)electrostatic forces
10. b)vibration spectroscopy
11. a)dielectric constant
12. d)a) and b)
13. d)All of the above
14. a)Fully solvent
15. d)ion triplet

References:

1. Martins Physical Pharmacy, 6th edition 2011, page no. 332-355.

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