Solutions and Concentration: Chemistry

• A solution is a homogeneous mixture.
• Lemonade is an example of a solution where sugar/salt (solute) is dissolved completely in water (solvent).

Components of a Solution

• Solute is the substance being dissolved.
• Solvent is the substance in which the solute is dissolved.

Types of Solutions Based on Components

• Binary Solution: one solvent + one solute (2 components total)
• Ternary Solution: one solvent + two solutes (3 components total)
• Quaternary Solution: one solvent + three solutes (4 components total)
• Assume a binary solution if not specified.

Concentration of Solutions

• Concentration indicates the amount of solute in a solvent.
• Ways to express concentration:
  • Molarity (M)
  • Molality (m)
  • Mass/Volume Percentage
  • Mass/Mass Percentage
  • Volume/Volume Percentage
  • Mole Fraction
  • Parts Per Million (ppm)

Molarity (M)

• Molarity is defined as the number of moles of solute per liter of solution.
• M = moles of solute / volume of solution in liters

Molality (m)

• Molality is defined as the number of moles of solute per kilogram of solvent.
• m = moles of solute / mass of solvent in kg

Mass by Volume Percentage

• Represents the mass of solute in grams in 100 mL of solution.
• Mass/Volume % = (mass of solute in grams / volume of solution in mL) × 100

Mass by Mass Percentage

• Represents the mass of solute in grams in 100 grams of solution.
• Mass/Mass % = (mass of solute in grams / mass of solution in grams) × 100

Volume by Volume Percentage

• Represents the volume of solute in mL in 100 mL of solution.
• Volume/Volume % = (volume of solute in mL / volume of solution in mL) × 100

Mole Fraction

• Represents the ratio of moles of a component to the total moles in the solution.
• Mole Fraction (X) = moles of component / total moles in solution

Parts Per Million (ppm)

• Represents the mass of solute in grams per 10^6 grams of solution.
• ppm = (mass of solute in grams / mass of solution in grams) × 10^6

Vapor Pressure

• Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid.
• Raoult's Law: The partial vapor pressure of a component in a solution is proportional to its mole fraction.

Raoult's Law for Volatile Solutes

• P_a = P_a^0 * X_a, P_b = P_b^0 * X_b
  • P_a and P_b are the partial pressures
  • P_a^0 and P_b^0 are the pure vapor pressures
  • X_a and X_b are the mole fractions

Vapor Pressure of Non-Volatile Solutes

• Vapor pressure decreases when a non-volatile solute is added to a volatile solvent.
• Vapor pressure can be determined using Raoult's Law.

Homework Assignment

• Calculate the mass of H₂SO₄ in a 4 M solution with a density of 1.2 g/mL and also determine the moles of H₂SO₄ and the mass of the solution.