Solutions and Mixtures — Chemistry Unit 7 practice.
This unit covers solubility, concentration and colligative properties — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers solubility, concentration and colligative properties — essential concepts for Chemistry. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Solubility
Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. Students must understand how temperature and pressure affect solubility for both solids and gases. The rule 'like dissolves like' governs whether a solute will dissolve in a given solvent.
Key Points
- Solubility of most solids increases as temperature increases; solubility of gases decreases as temperature increases
- Pressure has little effect on solid/liquid solubility but significantly affects gas solubility (Henry's Law)
- Polar solvents dissolve polar and ionic solutes; nonpolar solvents dissolve nonpolar solutes
- A saturated solution holds the maximum dissolved solute; supersaturated solutions are unstable and hold more than the normal maximum
Which substance is more soluble in water: NaCl or I₂? Which is more soluble in hexane (C₆H₁₄)?
Water is a polar solvent, so it dissolves NaCl (ionic/polar) much better than I₂ (nonpolar). Hexane is a nonpolar solvent, so I₂ dissolves readily in hexane while NaCl does not. This directly applies the 'like dissolves like' principle tested on most exams.
2 Concentration
Concentration describes the amount of solute dissolved in a given quantity of solution or solvent. Students must be able to calculate and convert between molarity (M), percent by mass, and parts per million (ppm). Dilution problems using M₁V₁ = M₂V₂ are heavily tested.
Key Points
- Molarity (M) = moles of solute ÷ liters of solution
- Percent by mass = (mass of solute ÷ mass of solution) × 100
- Dilution formula: M₁V₁ = M₂V₂ — moles of solute are conserved when adding solvent
- To prepare a solution, calculate moles needed, convert to grams, dissolve and dilute to the target volume
How many mL of a 6.0 M HCl stock solution are needed to prepare 250 mL of a 0.50 M HCl solution?
Apply M₁V₁ = M₂V₂: (6.0 M)(V₁) = (0.50 M)(0.250 L), so V₁ = 0.125 ÷ 6.0 = 0.0208 L = 20.8 mL. You would measure 20.8 mL of stock HCl and add water until the total volume reaches 250 mL. The number of moles of HCl stays the same; only the volume changes.
3 Colligative Properties
Colligative properties depend only on the number of dissolved solute particles, not their identity. The four colligative properties are boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. Students must be able to calculate ΔTb and ΔTf using the formulas with molality and the van't Hoff factor.
Key Points
- ΔTf = Kf × m × i and ΔTb = Kb × m × i, where m = molality and i = van't Hoff factor (number of particles per formula unit)
- Ionic compounds split into ions: NaCl → i = 2; CaCl₂ → i = 3; molecular compounds → i = 1
- Adding solute lowers freezing point and raises boiling point relative to pure solvent
- Osmosis moves water through a semipermeable membrane from low solute concentration to high solute concentration
What is the freezing point of a solution made by dissolving 58.5 g of NaCl in 1.00 kg of water? (Kf for water = 1.86 °C/m)
First find moles of NaCl: 58.5 g ÷ 58.5 g/mol = 1.00 mol. Molality = 1.00 mol ÷ 1.00 kg = 1.00 m. NaCl dissociates into Na⁺ and Cl⁻, so i = 2. ΔTf = 1.86 × 1.00 × 2 = 3.72 °C, meaning the freezing point drops to −3.72 °C instead of 0 °C.
Questions, answered.
What is Solutions and Mixtures?
Solutions and Mixtures is Unit 7 of Chemistry, covering solubility, concentration and colligative properties.
How to study for Chemistry Unit 7?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 25+ review questions across 5 different game modes.