Solutions and Molarity

The substance that is more plentiful in a solution

The substance that is less plentiful in a solution

A homogeneous mixture of two or more substances

Molarity is the most common method to represent the concentration of solute particles in solution. $\text{Molarity} = \frac{\text{mol solute}}{\text{L solution}}$

A 3.75g sample of NaCl is dissolved in water. The total volume of the solution is 768mL. What is the molarity of the solution?

$3.75\text{g NaCl} \times \frac{1 \text{ mol NaCl}}{58.44 \text{ g NaCl}} = 0.0642 \text{ mol NaCl}$

$\text{Molarity} = \frac{0.0642 \text{ mol}}{0.768 \text{ L}} = 8.36\times10^{-2} \text{ M NaCl}$

When ionic compounds dissolve in water, it dissociates. These are known as electrolytes.

Common electrolytes include:

• NaCl (salt)
• NaNO₃ (sodium nitrate)
• CaCl₂ (calcium chloride)

Lowering the concentration of solution (by adding more solvent). To determine the concentration of a solution, you can use the Dilution Equation.

$M_1V_1 = M_2V_{total}$

Note that $M*V = \text{moles}$. $M$ represents molarity and $V$ volume.

What if a 1M 10mL solution was diluted with 10mL extra water?

• $1M \times 10\text{mL} = ?M \times 20\text{mL}$
• $M = 0.5M$ The result is a halved molarity!