Solutions, Henry's law

SOLUTIONS

When two or more than two substances are mixed with each other but do not react with each other it is called a solution.

Solutions are of two types

Homogeneous Solutions are mixtures of two or more than two components whose composition and properties are uniform throughout the mixture. Heterogeneous mixture don’t have uniform composition and properties

BINARY SOLUTIONS

Binary solution is a solution which contains only two components which are called solute and solvent

Solvent: The component whose mole fraction is greater than other

Solute: The component whose mole fraction is smaller than solvent

TYPES OF BINARY SOLUTIONS

CONCENTRATION OF BINARY SOLUTIONS

If we take a binary solution consisting of A & B.

1. Mass percentage :
2. Volume percentage :
3. Mass/volume percentage =
4. Parts per million (ppm) =

Solution

5. Mole fraction: moles of A in one mole of solution  
6. Molality: mole of A in one kg of B   
7. Molarity: moles of A in one litre of solution (A + B)   
8. Normality: gm eqn. of A per lite of solution

SOLUTION OF GASES IN LIQUIDS

HENRY’S LAW

The mole fraction of volatile solute is proportional to the vapor pressure of the solute.

P = K_HX

K_H= Henry‘s Law constant, X = mole fractions.

Increasing the partial pressure of a gas over a liquid increases the amount of gas dissolved in the liquid

K_H depends on temperature

Henry’s law finds several applications in industry

To increase the solubility of CO₂ in soft drinks and soda water, the bottle is sealed under high pressure

Bends: Scuba divers while breathing air at high pressure underwater increases the solubility of atmospheric gases in blood. When the divers come towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends, which are painful and dangerous to life

Anoxia: at high altitudes due to low pressure the solubility of oxygen in blood decreases.

Effect of temperature, pressure and different gases

Temperature: Increase in temperature leads to less solubility of gases in liquid. 

This can be explained by kinetic theory as well as thermodynamics

Types of Gases: Heavier gases have more solubility. At same temperature and pressure as compared to lighter gases. (Value of ‘a’)

Pressure: Increase in pressure leads to greater solubility of gases in liquids.

SOLUTIONS LIQUID IN LIQUID

In this Section, we shall discuss the solutions of liquids and solids in a liquid. Such solutions may contain one or more volatile components. Ex: water-alcohol

• Solubility: Solubility of a substance is defined as the maximum amount of substance that can be dissolved in a specified amount of solvent to a given temperature
• Saturated solution : A solution in which no more solute can be dissolved at the same temperature and pressure is called a saturated solution
• Effect of temperature: mass %, mole fraction and molality do not change with temperature whereas Molarity changes with temperature because volume of solution (liquid) changes with temperature.
• Effect of dilution;-Moles, milli-moles, equivalent, milli-equivalent of solute does not change on dilution, but Molarity , molality and mole fraction change with dilution
• Like dissolves like: Polar solutes dissolve in polar solvents and non-polar solutes dissolves in non-polar solvents. In general, a solute dissolves in a solvent if the intermolecular attractions are similar in both.

A liquid may or may not be solute in another liquid Depending upon the relative solubility of a liquid in another the following three cases are possible:

Miscible liquid form three types of solution, which can be ideal or non ideal solutions.

When solute and solvent both are Volatile

Volatile: When the vapour pressure of substance is low. Ex. Ethyl alcohol, hexane etc.

Non Volatile: When the vapour pressure of substance is high. All solids are non-volatile. Some liquids like Glycerol etc. are non-volatile.