IB Chemistry: Unit 2- Solutions

Key Concepts of Solutions and Concentration

Concentration Formula

  • Concentration (C): The amount of solute per volume of solution. Utilized formula:

    • C = n/v

    • Where:

      • n = number of moles

      • v = volume in liters

Understanding Moles

  • Moles of Solids:

    • Formula: n = m / M

      • Where:

        • m = mass of the solid

        • M = molar mass of the solid

  • Moles in Solutions:

    • Needs concentration and volume to determine moles.

    • Use the formula: n = C × V

Solvents and Solutes

  • Solvent: The component of a solution that is present in the greatest amount.

    • Water is commonly used as a universal solvent, especially in this unit.

  • Solute: The substance that is dissolved.

    • Example: Sodium chloride (NaCl) when dissolved in water.

Aqueous Solutions

  • Use of the aqueous (aq) notation to indicate substances dissolved in water.

    • Example: Sodium chloride (NaCl) in solution becomes Na⁺(aq) + Cl⁻(aq)

Saturation of Solutions

  • Saturated Solution: The point at which no more solute can be dissolved in the solvent.

    • Concentration cannot increase beyond this point.

    • Different solutes have different saturation points.

Measuring Concentration

  • Concentration can be measured in various units, but the common ones are:

    • Moles per liter (mol/L or M)

    • Moles per decimeter cubed (mol/dm³)

  • Conversions:

    • 1 liter = 1 decimeter cubed (1 L = 1 dm³)

Problem Solving Related to Concentration

  • Example Problem: Calculate the concentration of a solution.

    • Given: 25.5 grams of sodium hydroxide (NaOH) dissolved in water with a total volume of 2 dm³.

    • Steps:

      1. Calculate moles using molar mass of NaOH.

      2. Use concentration formula: C = n/V.

Dilution and Concentration Relationship

  • Dilution: If water is added to a solution, the moles of solute remain the same, but the volume increases, thereby lowering the concentration.

  • Dilution Formula:

    • c1v1 = c2v2

      • Where:

        • c1 = initial concentration

        • v1 = initial volume

        • c2 = final concentration

        • v2 = final volume.

  • Example: To dilute a concentrated solution to a specific concentration, rearrange to solve for the unknown.

Summary of Chemical Solutions

  • Solutions are composed of solutes dissolved in solvents, with water being the primary solvent in most cases studied.

  • Concentration is key to understanding and calculating different properties of solutions, including how to prepare solutions and how to manipulate their concentrations during chemical reactions.