Chem 2

Molarity ($M$)

Molarity is a measure of concentration defined as the number of moles of solute dissolved per unit volume of solution.

• Formula: $M = \frac{n}{V}$

  • $n$ represents the amount of solute in moles ($mol$).

  • $V$ represents the total volume of the solution in cubic decimeters ($dm^3$).

• Units:

  • Expressed in $mol\,dm^{-3}$ or molar ($M$).

• Temperature Dependence:

  • Molarity is temperature-dependent because the volume of a liquid solution expands or contracts as temperature changes, altering the concentration.

Molality ($m$)

Molality is a measure of concentration defined as the number of moles of solute dissolved per mass of solvent in kilograms.

• Formula: $m = \frac{n<em>{solute}}{m</em>{solvent}}$

  • $n_{solute}$ represents the amount of solute in moles ($mol$).

  • $m_{solvent}$ represents the mass of the solvent in kilograms ($kg$).

• Units:

  • Expressed in $mol\,kg^{-1}$ or molal ($m$).

• Temperature Independence:

  • Molality is independent of temperature because mass does not change with temperature changes. This makes it useful in studying colligative properties such as freezing point depression and boiling point elevation.

Dilution

Dilution is the process of reducing the concentration of a solute in a solution by adding more solvent.

• Core Principle:

  • The total amount of solute in moles remains constant before and after dilution:
    $n<em>1 = n</em>2$

• Dilution Equation: $M<em>1 V</em>1 = M<em>2 V</em>2$

  • $M_1$ represents the initial molarity ($mol\,dm^{-3}$).

  • $V_1$ represents the initial volume ($dm^3$ or $cm^3$).

  • $M_2$ represents the final molarity ($mol\,dm^{-3}$).

  • $V_2$ represents the final total volume ($dm^3$ or $cm^3$).