AP Chemistry Unit 3.8 Representation of Solution

Representation of Solution

  • Molarity (M): K.A Concentration
      • Ex: A solution that is 1.0 molar (written as 1.0 M) contains 1.0 mole of solute per liter of solution.
  • Note: brackets around something it means the “molarity of what is inside”
  • Dilution: water is added to achieve the molarity desired for a particular solution
      • Does not change the amount of moles present
  • Mass percent (weight percent): 
  • Molality:
  • Normality (N): Molarity x number of equivalents (definition of an equivalent depends on the reaction taking place in the solution)
    • Acid–base reaction → number of protons = equivalents
    • Oxidation–reduction reactions → number of e- in half-reaction = equivalents

Calculating Concentration of Ions

  • Write out balanced formula for dissolution reaction
  • Ex: 35g CaCl2 dissolved in 2.75L

Mole Fraction, Mass Percent, & Density Questions

  • Find moles → mass percent / molar mass
  • Molarity = (MP as a decimal )(1000)(density/molar mass)
  • Remember that Density = g/cm3 (mL)
    • With water (d =1g/cm3) can just convert mL to grams

Steps in Solution Formation

  1. Overcoming solute-solute interactions (endothermic) (ΔH₁)
    • Breaking ionic compound= breaking ionic bonds; breaking covalent solute = breaking interMF
  1. Expanding the solvent (endothermic) (overcoming interMF) to make room for the solute (ΔH₂)
  2. Allowing the solute and solvent to interact to form bonds and a solution (exothermic) (ΔH₃)
    • Enthalpy (heat) of solution (ΔHsoln): is the sum of the ΔH values for the steps of solution formation
      • Might have a positive sign (energy absorbed) or a negative sign (energy released)
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