Understanding how to express the concentration of solutions is fundamental in chemistry, particularly for exams like JEE and NEET. Here are the key concepts and methods used to express concentration.

1. Molarity (M)

Definition: Molarity is the number of moles of solute present in one liter of solution.

Formula:

Molarity (M) = Number of moles of solute/Volume of solution in liters

2. Molality (m)

Definition: Molality is the number of moles of solute present in one kilogram of solvent.

Formula:

Molality (m)= Number of moles of solute/Mass of solvent in kilograms

3. Normality (N)

Definition: Normality is the number of gram equivalents of solute present in one liter of solution.

Formula:

Normality (N) = Number of gram equivalents of solute/ Volume of solution in liters

4. Mole Fraction (χ)

Definition: Mole fraction is the ratio of the number of moles of a component to the total number of moles of all components in the solution.

Formula:

χA= Number of moles of component A/ Total number of moles of all components

5. Percentage Concentration

a. Mass Percentage (w/w%)

Definition: Mass percentage is the mass of solute divided by the total mass of the solution, multiplied by 100.

Formula:

Mass Percentage = Mass of solute/Total mass of solution×100

b. Volume Percentage (v/v%)

Definition: Volume percentage is the volume of solute divided by the total volume of the solution, multiplied by 100.

Formula:

Volume Percentage =Volume of solute/Total volume of solution×100

c. Mass-Volume Percentage (w/v%)

Definition: Mass-volume percentage is the mass of solute divided by the total volume of the solution, multiplied by 100.

Formula:

Mass-Volume Percentage = Mass of solute/Total volume of solution×100

6. Parts per Million (ppm) and Parts per Billion (ppb)

a. ppm

Definition: Parts per million is the number of parts of solute present in one million parts of the solution.

Formula:

ppm = Mass of solute/Total mass of solution ×10^6

b. ppb

Definition: Parts per billion is the number of parts of solute present in one billion parts of the solution.

Formula:

ppb = Mass of solute/Total mass of solution×10^9

7. Dilution Formula

When diluting a solution, the amount of solute remains constant before and after dilution. The relationship can be expressed as:

M_1 V_1 = M_2 V_2

where ( M_1 ) and ( V_1 ) are the molarity and volume of the concentrated solution, and ( M_2 ) and ( V_2 ) are the molarity and volume of the diluted solution.

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Important Points to Remember:

1. Molarity changes with temperature as it depends on volume.

2. Molality does not change with temperature since it depends on mass.

3. Normality depends on the reaction and the equivalent factor of the solute.

4. Mole Fraction is a dimensionless quantity and remains unaffected by temperature.

5. Percentage Concentrations are useful for expressing the concentration of solutions in everyday life, like in commercial products.

These methods of expressing concentration are crucial for solving various problems in chemistry, including those in competitive exams like JEE and NEET.