Define the following terms:
(i) Mole fraction
(ii) Molality
(iii) Molarity
(iv) Mass percentage.
(i) Mole fraction
(ii) Molality
(iii) Molarity
(iv) Mass percentage.
Solution and Explanation
(i) Mole Fraction
Definition:
Mole fraction is a way of expressing the concentration of a component in a mixture. It is defined as the ratio of the number of moles of one component to the total number of moles of all components in the mixture.
Formula:
\[\text{Mole Fraction (X)} = \frac{\text{Number of moles of component}}{\text{Total number of moles of all components}}\]
For a solution with components A and B:
\[X_A = \frac{n_A}{n_A + n_B}\]
\[X_B = \frac{n_B}{n_A + n_B}\]
where \( n_A \) and \( n_B \) are the number of moles of components A and B, respectively.
(ii) Molality
Definition:
Molality is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per kilogram of solvent.
Formula:
\[\text{Molality (m)} = \frac{\text{Number of moles of solute}}{\text{Mass of solvent in kilograms}}\]
For example, if 2 moles of solute are dissolved in 1 kilogram of solvent:
\[m = \frac{2 \text{ moles}}{1 \text{ kg}} = 2 \text{ mol/kg}\]
(iii) Molarity
Definition:
Molarity is another measure of concentration, defined as the number of moles of solute per liter of solution.
Formula:
\[\text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}}\]
For example, if 1 mole of solute is dissolved to make 1 liter of solution:
\[M = \frac{1 \text{ mole}}{1 \text{ liter}} = 1 \text{ M}\]
(iv) Mass Percentage
Definition:
Mass percentage is a way of expressing the concentration of an element or component in a mixture. It is defined as the mass of the component divided by the total mass of the mixture, multiplied by 100%.
Formula:
\[\text{Mass Percentage} = \left( \frac{\text{Mass of component}}{\text{Total mass of mixture}} \right) \times 100\%\]
For example, if a solution contains 5 grams of solute in 95 grams of solvent, the mass percentage of the solute is:
\[\text{Mass Percentage} = \left( \frac{5 \text{ g}}{5 \text{ g} + 95 \text{ g}} \right) \times 100\% = \left( \frac{5}{100} \right) \times 100\% = 5\%\]
These definitions provide a clear understanding of different ways to express concentrations of solutions in chemistry.
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Concepts Used:
Concentration of Solutions
It is the amount of solute present in one liter of solution.
Concentration in Parts Per Million - The parts of a component per million parts (106) of the solution.
Mass Percentage - When the concentration is expressed as the percent of one component in the solution by mass it is called mass percentage (w/w).
Volume Percentage - Sometimes we express the concentration as a percent of one component in the solution by volume, it is then called as volume percentage
Mass by Volume Percentage - It is defined as the mass of a solute dissolved per 100mL of the solution.
Molarity - One of the most commonly used methods for expressing the concentrations is molarity. It is the number of moles of solute dissolved in one litre of a solution.
Molality - Molality represents the concentration regarding moles of solute and the mass of solvent.
Normality - It is the number of gram equivalents of solute present in one liter of the solution and it is denoted by N.
Formality - It is the number of gram formula present in one litre of solution.