Thursday, May 6, 2010


A mixture or a substance containing two or more than two components which are mixed uniformly making a homogenous dispersion of molecules.

Components of solution:
There are two components of solution:
1. Solute
The component of the solution that is dispersed or dissolved throughout the other component.

2. Solvent
The component of the solution in which the dispersion or dissolution of the solute occurs.

Normally, larger quantity is that of solvent except in some cases as in syrup which can have 65% of sucrose as solute in aquous solution.
Sometimes, it is also difficult to distinguish between solute and solvent as in the case of miscible liquids such as alcohol and water. In this case, one component is considered as solvent and the other as solute.

Methods of expressing the concentration of the solution:
The concentration of the solution can be expressed in terms of the followings:

1. Molarity of the solute:
It represents the number of moles of solute in a given mass of solvent i.e. Number of moles of solute/Given mass of solvent.
Its unit is "mole/kg".

2. Concentration of the solute:
It represents the number of moles of solute in a given volume of solutiont i.e. Number of moles of solute/Given volume of solution.

Its unit is "mole/cubic meter".
Concentration can also be expressed in terms of the volume or mass of a solute in a given volume or mass of solution i.e. volume or mass of a solute/volume or mass of solution

3. Percentage expressions:
It can be represented by the following:
Volume or mass of a solute/volume or mass of solution x 100

It has following four forms:
1. Percentage weight in volume (% w/v)
2. Percentage weight in weight (%w/w)
3. Percentage volume in weight (%v/w)
4. Percentage volume in volume (%v/v)

Types of Solutions:

1. Types of Solutions on the basis of matters:
Solution may have any of the following types:
1. Gas in Gas solution
2. Gas in Liquid solution e.g. Oxygen in Water solution
3. Gas in Solid solution e.g. Dissolution of Hydrogen in Palladium
4. Liquid in Gas solution
5. Liquid in Liquid solution e.g. Ethanol in Water solution
6. Liquid in Solid solution e.g. Mercury in Gold
7. Solid in Gas solution
8. Solid in Liquid solution e.g. Sucrose in Water or NaCl (Salt) in Water solution
9. Solid in Solid solution e.g. Bronze and other Alloys

(Sometimes, the solutions of gases are considered as mixtures.)

2. Types of Solutions on the basis of Physical pharmacy:

1. Unsaturated solution:
It is a type of solution in which the solvent has the ability to dissolve more of the substance.

2. Saturated solution:
It is a type of solution in which the solvent contains maximum amount of absorbed solute.

3. Supersaturated solution:
It is a type of solution in which the solvent contains more than dissolvable amount of solute.

It represents the ability of one substance to be dissolved in another substance at a given temperature and pressure.
On the basis of solubility two types of substances are identified:
1. Miscible:
Substances that can be easily mixed into each other e.g. ethanol in water.

2. Immiscible:
Substances that cannot be easily mixed into each other or are not able to be mixed into each other e.g. oil in water.

Factors affecting Solubility:
1. Nature of solute and solvent
2. Temperature:Temperature may have varying effects of solubility. Solubility of many solids in water normally increases with temperature. This increase in solubility is upto 100 C. But on the other hand, there are certain substances, such as cerium (III) sulphate, which become less soluble on increasing the temperature.

3. Pressure
4. Common ion and ionic strength of solution
5. Polarity:
Here the common notion of "like dissolves like" works. It means the polar substances like urea are more soluble in polar substances like water and on the other hand non-polar substances like naphthalene is more soluble in non-polar substances like benzene.

Dissolution represents the process by which molecules or ions of solvent form a bond with molecules or ions of solute resulting in the formation of a solution. In this case, the bond is weak. It is also referred to as solvation.

Dissolution ~ Solvation

Dissolution also refers to the breakdown of something (solid in nature) into little basic parts or constituents which results in the transport of particles into  the solvent.

In the case of ionic compounds, dissolution is resulted after the ionization of the compounds and this happens mostly in the case of polar substances like ammonia and water. If we put NaCl in water, it will ionize as follows and then dissolve in water.

NaCl(s) → Na+(aq) + Cl-(aq)

One of the most law for the dissolution studies is Nernst Distribution law.

Nernst Distribution law:
This law represents the ratio of the distribution of a substance in two liquids which are either miscible or immiscible.

This law states that the ratio of the distribution or concentration of a substance in two liquids at equilibrium is constant.
This law is represented by the following equation:

Rate of dissolution:
Following factors affect the rate of dissolution:
1. Nature of the solvent and solute
2. Temperature
3. Mixing
4. Surface area of the particles
5. Degree of saturation

Multiple Choice Questions (MCQs) of Solutions from Pharmaceutics
1. A liquid preparation that contains one or more dissolved (molecularly dispersed) chemical substances in a suitable solvent or mixture of miscible solvents ;may be oral, parentral, topical, otic, ophthalmic is generaly called as;

a. Liquid
b. Semisolid
c. Emulsion
d. Solution
e. Paint
f. Injection
g. Infusion
2) Select a pahrmaceutical preparation.which is the example of solution;

a. Crimaffin emulsion
b. Brufen suspension
c. Betnovate-N cream
d. Hydraline syrup (Actually it is Hydryllin syrup)
3) Select a pharmaceutical preparation,which is an example of topical solution;

a. Kaolin poultice
b. Pyodine
c. Polyfex
4) Which statement is true for solutions;

a. They are semisolids
b. They should be shaken before use
c. They not to be shaken before use
d.They are example of suspensions
5) Select  pharmaceutical dosage form,which is not solution;

a. Phenergan elixir
b. Tincture iodine
c. Tincture  benzoinco
d. Tixilyx elixir
e. Nedex pluse lotion (stefel)
6) In allergic conditions as a first aid we can use;

a. Acetaminophen syrup
b. Antihistamine syrup
c. Ferrous sulfate syrup
7) Which example of solution has no volatile-content;

a. Digoxin elixir
b. Salicylic acid collodion
c. Aromatic waters
d. Syrup
e. Dexamethasone elixir
f. Spirit
8) All the solutions of same molarity contain the _________ number of molecules

a. Different
b. Same
c. Million
d. Zero
9) Can we use solutions in the form of a spray(aerosol system)

a. No
b. Yes
c. Ignore it
10) Colligative properties have a relation with;

a. Suspension
b. Emulsion
c. Solution
d. Ointments
e. Lotions
Answers to Multiple Choice Questions (MCQs) of Solutions from Pharmaceutics
1. d
2. d
3. b
4. c
5. e
6. b
7. d
8. b
9. b
10. c

(These MCQs are helpful for the preparation of Pharmacy Exams)
Further Studies:

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