Solutions and Mixtures

Grade 10 · Science · Study Guide

Understand the properties of solutions, factors affecting solubility, concentration calculations, and colligative properties.

A solution is a homogeneous mixture of two or more substances uniformly distributed at the molecular level. The solvent is the dissolving medium (present in the greater amount), and the solute is the dissolved substance. Solutions can be solids, liquids, or gases dissolved in liquids — or any combination.

Solubility describes the maximum amount of solute that dissolves in a given amount of solvent at a specific temperature. The "like dissolves like" rule states that polar solvents dissolve polar and ionic solutes, while nonpolar solvents dissolve nonpolar solutes. Temperature generally increases solubility of solids but decreases the solubility of gases. Pressure affects gas solubility (Henry's Law).

Concentration measures how much solute is dissolved per unit of solution. Molarity (M) is the most common unit: M = moles of solute ÷ liters of solution. Percent by mass and parts per million (ppm) are also used.

Colligative properties depend only on the number of dissolved particles, not their identity. These include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. When a solute is dissolved, it raises the boiling point and lowers the freezing point of the solvent proportionally to the solute's molality.

Key terms

Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure
Molarity (M): Concentration expressed as moles of solute per liter of solution: M = n/V
Colligative property: A property that depends on the number of dissolved solute particles, not their chemical identity
Saturated solution: A solution containing the maximum amount of dissolved solute at a given temperature; at equilibrium with undissolved solute
Henry's Law: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid
Electrolyte: A substance that dissociates into ions when dissolved, allowing the solution to conduct electricity (e.g., NaCl, HCl)

Flashcards

Solution components: Solvent (dissolves; greater amount) + solute (dissolved; lesser amount) = homogeneous mixture
Molarity formula: M = moles of solute / liters of solution; unit is mol/L or M
Dilution formula: M₁V₁ = M₂V₂; moles of solute are conserved when diluting a solution
Unsaturated solution: Solution that can dissolve more solute; concentration is below the solubility limit
Supersaturated solution: Unstable solution containing more dissolved solute than the saturation limit; crystallizes readily
Boiling point elevation: ΔTb = Kb × m × i; dissolved solutes raise the boiling point of a solvent proportional to their molality
Freezing point depression: ΔTf = Kf × m × i; dissolved solutes lower the freezing point; explains road salt and antifreeze
Osmosis: Movement of solvent through a semipermeable membrane from low to high solute concentration

Questions

What is the molarity of a solution containing 0.5 moles of NaCl dissolved in 250 mL of solution?
1. 0.5 M
2. 1.0 M
3. 2.0 M
4. 0.125 M
Show answer
Answer: 2.0 M
M = moles / liters = 0.5 mol / 0.250 L = 2.0 M
According to the 'like dissolves like' principle, a nonpolar solvent like hexane will dissolve ionic compounds like NaCl easily.
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Answer: False
NaCl is ionic and polar; hexane is nonpolar. Polar/ionic solutes dissolve in polar solvents, not nonpolar ones ('like dissolves like')
A solution that contains the maximum amount of dissolved solute at a given temperature is called a ________ solution.
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Answer: saturated
A saturated solution is at equilibrium with undissolved solute — the maximum amount of solute has dissolved at that temperature
Which of the following is an example of a colligative property?
1. The color of a solution
2. The solubility of a salt
3. Freezing point depression
4. The reactivity of the solute
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Answer: Freezing point depression
Colligative properties (boiling point elevation, freezing point depression, osmotic pressure) depend on particle count, not solute identity
Which factor generally increases the solubility of a gas in water?
1. Increasing temperature
2. Decreasing pressure
3. Increasing pressure
4. Adding more water
Show answer
Answer: Increasing pressure
Henry's Law: gas solubility is directly proportional to partial pressure. Increasing pressure forces more gas into solution (e.g., carbonated beverages)

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