Core Concept

Molarity (M) is a unit of concentration used to describe how much solute is dissolved in a given volume of solution. It is defined as the number of moles of solute per liter of solution.

Molarity Formula

Molarity is calculated using the formula:

$M = \frac{\text{moles of solute}}{\text{liters of solution}}$

Where:

• M = Molarity of the solution (in moles per liter, or mol/L)

• Moles of solute = The amount of solute in moles

• Liters of solution = The total volume of the solution in liters

Key Concepts

1. Solute and Solvent:

   • Solute: The substance that is dissolved (e.g., salt in a saltwater solution).

   • Solvent: The substance in which the solute is dissolved (e.g., water in a saltwater solution).

   • Solution: The homogeneous mixture of solute and solvent.

2. Units of Molarity:

   • Molarity is measured in moles per liter (mol/L), often abbreviated as M.

   • For example, a 1.0 M solution of NaCl contains 1 mole of NaCl dissolved in 1 liter of solution.

3. Dilution:

   • Diluting a solution reduces its molarity by adding more solvent.

   • Dilution formula: $M_1 V_1 = M_2 V_2$​

   • Where:

     • $M_1$​ and $V_1$​: Initial molarity and volume

     • $M_2$​ and $V_2$: Final molarity and volume

4. Preparing Solutions:

   • To prepare a solution of a given molarity, calculate the moles of solute needed, then dissolve it in enough solvent to reach the desired final volume.

Steps for Calculating Molarity

1. Calculate Moles of Solute:

   • If the amount of solute is given in grams, convert it to moles using the molar mass of the solute. $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$

2. Determine Volume of Solution in Liters:

   • Convert the solution volume to liters if necessary (1 L = 1000 mL).

3. Apply the Molarity Formula:

   • Substitute the moles of solute and the liters of solution into the formula: $M = \frac{\text{moles of solute}}{\text{liters of solution}}$