Unit 5-1: Solutions and Molarity

Solutions

• Homogeneous mixtures are called solutions.
• The solute changes state, while the solvent keeps its state.
• If both components start in the same state, the major component is the solvent.

Solute Examples

• Gases can be solutes (e.g., fish breathing in water).
• Examples include soda drinks (CO2, sugar, and water) and seawater.

"Like Dissolves Like"

• Polar solutes dissolve best in polar solvents; nonpolar solutes dissolve best in nonpolar solvents.
• Nonpolar examples: Fats/oil, Benzene (C6H6), Steroids, Hexane, Waxes (CxHy), pure elements, and any hydrocarbon organic compound consisting only C and H.
• Polar examples: Soluble Salts, Water, Sugars ((CH2O)n), Small alcohols, Acetic acid.

Solubility Trends

• Solids: Higher solubility with heat, stirring, and smaller particle size.
• Gases: Higher solubility with colder temperatures and high pressure.

Solution Concentration

• Dilute solutions have less solute than concentrated solutions.
• Concentration of solute X(aq) is written as [x].

Molarity (M)

• Definition: Moles of solute per liter of solution.
• Unit: mole/L or M (molar).
• Formula: M = \frac{moles \, of \, solute}{liters \, of \, solution}

Molarity as a Conversion Factor

• Example: 2.0 M NaCl solution contains 2.0 moles of NaCl per liter.
• Use molarity to convert between moles and liters: mole = M \cdot L and L = \frac{mole}{M}

Preparing Solutions

• To find molarity, use: M = \frac{moles}{L}

Dilution of a Solution

• Stock solutions are concentrated and diluted by adding solvent.
• Moles of solute remain constant: M1 \cdot V1 = M2 \cdot V2
  • M1 = initial molarity, V1 = initial volume, M2 = final molarity, V2 = final volume