A solution is a homogeneous mixture of two or more substances.
The substance with largest amount is called solvent and other substances with lesser amounts are called solute.
Binary solution : A solution having only two components is called a binary solution.
Types of binary solutions : On the basis of the states of solvent, there are three types of solutions as follows:
1. Solid solutions : A solution in which the solvent is a solid is called a solid solution.
2. Liquid solutions : A solution in which the solvent is a liquid is called a liquid solution.
3. Gaseous solutions : A solution in which the solvent is a gas is called a gaseous solution.
◆ Concentration : The amount of solute present in a solution is called the concentration of the solution.
◆ Methods of expressing concentration :
1. Strength : The amount of the solute in grams present in one litre of a solution is called strength.
i.e. Strength = Mass of solute / Volume of solution(in L)
2. Mass Percent : The mass percent of the solute is expressed as follows :
Mass % = Mass of solute×100 / Mass of the solution
3. Volume Percent : The volume percent of a solution is defined as follows:
Volume % = Volume of the solute × 100/ Volume of the solution
4. Mole Fraction : If a binary solution has two components A and B having nA and nB moles then their mole fraction is denoted by xA & xB respectively where
xA = nA/(nA + nB) & xB = nB/(nA + nB)
Key Point : xA + xB = 1
5. Molality : The molality of a solution is defined as the moles of solute per kilogram of solvent i. e.
Molality = Moles of solute / Mass of solvent(In Kg)
Key Point : Molality is denoted by ‘m’.
6. Molarity : The molarity of a solution is defined as the number of moles per litre of the solution i. e.
Molarity = Moles of the solute /Volume of the solution(In Litre)
Key Point : I. Molarity is denoted by ‘M’.
II. If the molarity of a solution changes from M1 to M2 and it’s volume changes from V1 to V2 then M1V1 = M2V2
III. Molality doesn’t change with change in temperature because it depends upon mass whereas molarity is affected by temperature because of its dependence on volume.