Solutions

• 2 Types of Matter: Pure and Mixture
• Pure: Elements and Compounds; Mixture: Heterogeneous and Homogeneous
• Homogeneous: Colloid and Solution
• Solutions - a homogeneous mixture made up of ions, atoms, molecules
• components

  • solute - dissolved medium
  • solvent - dissolving medium
• solubility - refers to the amount of solute that can dissolve in a given amount of solvent at room temperature under given conditions
• 3 Types of Solutions

  1. Unsaturated - more solute dissolves
  2. Saturated - no more solute dissolves
  3. Supersaturated - crystals may grow
• Types of Reactions

  1. Exothermic reactions - releases energy from the system in the form of heat
  2. Endothermic reactions - the system absorbs energy from it’s surrounding in the form of heat
• Factors That Affect Solubility

  • Nature of the Solute & Solvent
  • Effect of Temperature
  • Effect of Pressure
  • Surface Area
• nature of the solute and solvent

  - “like dissolves like”

  - solute: nonpolar solvent: polar = insoluble/immiscible
• solubility of gas in liquid

  • the solubility of gas in liquid increases with a decrease in temperature and vice versa
  • lower temperature = higher solubility

  solubility of solid in liquid (in general)

  endothermic reactions

  : solubility of solids increases with an increase in temperature

  : A + B + heat -> AB

  exothermic reactions

  : solubility of solids decrease with an increase in temperature

  : A + B -> AB + heat
• effect of pressure

  • when pressure is increased, molecules or ions come closer to each other and chances for interaction between the solute and solvent increases
  • solubility of gas in liquids increases with an increase in pressure
• effervescence: fizz
• surface area

  • the greater the surface area, the greater the interaction of the solute and solvent, and thus solubility increases
• stirring

  • as the solute is added to the solvent, solute particles tend to concentrate in a section of the mixture, slowing down the dissolution process
  • disperses the solute particles into other sections of the solvent
• colligative properties

  • depend solely on the number of particles of solute present but not on the kind and nature of solute
• colligative properties

  • vapor pressure reduction
  • boiling point elevation
  • freezing point depression
  • osmotic pressure
• vapor pressure reduction

  • the non-volatile solute molecules take up space at the surface, thus preventing the escape of the solvent molecules
  • the interaction between the solute and the solvent is greater than the solvent-solvent interaction
• more solute = lower vapor pressure

  the greater the concentration = the greater the vapor pressure reduction
• boiling point elevation

  • higher vapor pressure = low boiling point
  • it takes up higher temperature to attain the boiling point of a solution
  • the greater the concentration = the greater the boiling point of the solvent
• ΔTb = Tb sol’n - Tb solvent

  ΔTb = Kb m

  Kb = molal boiling point constant

  m = molality
• freezing point depression

  • if a non-volatile solute is added to a solvent, the freezing point of the solvent is lowered
  • the amount by which the freezing point temperature of a solvent is lowered
• ΔTf = Tf solvent - Tf sol’n

  ΔTf = Kf m
• osmotic pressure

  • the difference of pressure between the two sides during osmosis

  osmosis - the movement of solvent through a semipermeable membrane from a region of high concentration
• Π = nRT/v = MRT

  n = number of moles

  T = temperature in K

  v = volume

  M = molar mass

  R = ideal gas constant
• concentration

  • amount of solute present in a given amount of solvent
• different ways of expressing concentrations:

  1. percent by mass - m/m% = mass of solute/mass of sol’n x 100
  2. percent by mass volume - m/v% = mass of solute/volume of sol’n x 100 (m=g v=mL)
  3. percent by volume - v/v% = volume of solute/volume of sol’n x 100
  4. percent per million - ppm = mass of solute/mass sol’n x 1,000,000
• molarity

  • the ratio of the number of moles of solute per liter of sol’n

  M = mol solute/L of sol’n

  unit = M: molar (mol/L)
• molality

  • the ratio of the number of moles of solute per kg of solvent

  M = mol solute/kg solvent

  unit = m: molal (mol/kg)
• mole fraction

  • the ratio of the number of moles of one component to the total num of moles in a sol’n

  Xa = mol solute/mol sol’n

  Xb = mol solvent/mol sol’n

  Xa + Xb = 1
• titration - one way of determining concentration of a solution of unknown concentration. it requires precision when done manually.
• 2 solutions for titration: titrant and titrand
• titrant

  • with known concentration
  • basic solution
  • placed in the buret
  • bases with low concentration
• titrand (analyte)

  • with unknown concentration
  • acidic solution
  • placed in the erlenmeyer flask
• end point

  • indicates that enough of the titrant has been added to make it react with the unknown solution
  • to know the end point, a phenolphthalein indicator is placed
• base + acid = neutralization
• very faint pink = reached the end point
• dilution

  C1V1 = C2V2
• materials for titration:

  • buret or burette
  • buret clamp
  • iron stand
  • erlenmeyer flask