Solutions & Concentration Cheat Sheet

Key Facts

• Molarity is calculated with $M = \frac{n}{V}$, where $n$ is moles of solute and $V$ is volume of solution in liters.
• Moles of solute in a solution can be found with $n = MV$, which is useful before doing stoichiometry.
• Dilution problems use $M_1V_1 = M_2V_2$ because the moles of solute stay constant when only solvent is added.
• Mass percent is calculated with $\%\ \mathrm{by\ mass} = \frac{m_{\mathrm{solute}}}{m_{\mathrm{solution}}} \times 100\%$.
• For dilute aqueous solutions, parts per million can be estimated with $\mathrm{ppm} \approx \frac{\mathrm{mg\ solute}}{\mathrm{L\ solution}}$.
• A saturated solution contains the maximum amount of dissolved solute at a given temperature and pressure.
• For most solid solutes, solubility increases as temperature increases, but gas solubility usually decreases as temperature increases.
• Strong electrolytes dissociate almost completely into ions, so $\mathrm{NaCl}(s) \rightarrow \mathrm{Na}^{+}(aq) + \mathrm{Cl}^{-}(aq)$ represents ion formation in water.

Vocabulary

Solution

A homogeneous mixture in which a solute is evenly distributed throughout a solvent.

Solute

The substance that is dissolved in a solution, such as $\mathrm{NaCl}$ in salt water.

Solvent

The substance that dissolves the solute and is usually present in the larger amount.

Molarity

A concentration unit equal to moles of solute per liter of solution, written as $M = \frac{n}{V}$.

Dilution

The process of lowering concentration by adding solvent while keeping the moles of solute constant.

Electrolyte

A substance that forms ions in solution and allows the solution to conduct electricity.