chapter 12: solutions

formation of solutions!

• dissolution: (dissolving) each solute particle is completely surrounded by solvent (h2o) particles

  • solute: soluble covalent compounds or ionics

  • to dissolve in water → polar

• dissociation: soluble, ionic compounds separate into ions (electrolytes, conductive*)

when dissolved!

three ways to dissolve a solid more quickly!

1. stir: (shake, agitate)

   1. solute comes in contact with solvent more often

2. decrease particle size: (grind)

   1. solute dissolves faster with more surface area

3. heat:

   1. particles moving aster more forceful collisions

   2. heat increases solubility of solids

solubility[mass (or number of mols) of solute / volume of solution/solvent]

factors affecting solubility

1. temperature

   1. solids dissolve better in warmer temperatures

   2. gases dissolve better in cooler temperatures

2. pressure

   1. solids dissolve easily in lower pressures

   2. gases dissolve easily in higher pressures

      1. this is HENRY’S LAW

saturation

**use solubility chart/curve

saturated: solution where is has the max amount of solute at a particular temperature

• (on line)

unsaturated: solution with less than the max amount of solute

• (under the line)

supersaturated: solution with more than the maximum amount of solute

• (above the line)

  • increase temperature so you can dissolve more and then cool it back down

  • created by

    • dissolve solute in warm solution, cool slowly (solid stays dissolved)

  • destroyed by

    • adding seed crystal (small piece of original solute)

    • stirring or shaking

difference between supersaturated solution and max amount of solution is what precipitates out

• left with → solid → saturated solution** (check this)*

concentration

expresses how much solute is dissolved in solvent

• concentrated: lots of solute

• dilute solution: only a little solute, compared to solvent

molarity (M)

moles of solute (n) per liter of solution (V)

M = (n/v) = (moles solute/liters of solution)

**dependent on temperature because volume of solution would change slightly

molality (cursive small ‘m‘)

moles solute per kilogram of solvent

m = (moles of solute / kg of solvent)

**not dependent on temperature!

parts per million (ppm) and parts per billion (ppb)

used for expressing very small concentrations, particularly for containments in environment

ppm = [ mass of solute (g) / vol of solution (mL)] * 10^6 (million)

ppb = [mass of solute (g) / vol of solution (mL)] * 10^9 (billion)

dilution

a dilute solute can be made by adding more solvent to a concentrated solution

• amount of solute stays the same

• of moles of solute stays the same

serial dilution!

colligative properties

• show how solutions behave differently than pure solvents

• depends of number of solute particles in solution, not type

• changes are more extreme when solutions are concentrated (more particles) rather than dilute

1. lower vapor pressure

   1. solute particles inhibit solvent from escaping as gas

      1. less gas → less pressure

2. boiling point elevation

   1. solute particles make it more difficult for solvent to escape as gas

   2. more energy needs to escape → higher temperature to boil

      1. determining ΔBP: ΔT = (i)(Kb)(m)

         1. ΔBP - change in temperature, not new boiling point

         2. i - # of disassociated particles

            1. VAN’T HOFF FACTOR

            2. i for all molecular compounds equals one!!

         3. Kb - boiling constant, unique for each constant

         4. m - molality: moles solute/kg solven

3. freezing point depression

   1. solute particles prevent pure solvent from forming

      1. cold temp needed to form solid

         1. determining ΔFP: ΔT = (i)(Kf)(m)

            1. ΔT - change in freezing point

            2. i - # of particles

            3. Kf - freezing constant

            4. m - molality

4. osmotic pressure

   1. osmosis: the movement of H2O through semi-permeable membrane

      1. increases as the difference in concentration increases

      2. * applying force to stop water from moving across the membrane

         1. force is known as osmotic pressure