Solutions – Chapter 15
Define these terms:
Solute
Immiscible
Electrolyte
Saturated solution
Nonvolatile solute
Colligative properties
Molality
Dynamic Equilibrium
Colloid
Suspension
Heat of solution
Solvent
Solvation
Unsaturated solution
Supersaturated solution
Vapor pressure
Molarity
Miscible
Solubility
Hydration
Tyndall Effect
Dissociation
What kinds of things are soluble in water?
1. Ionic compounds – water molecules surround
and pull off the individual ions (hydration)
2. Polar covalent compounds- pos and neg ends of
molecule are attracted to pos and neg ends of
water molecule.
Factors the Affect Solubility
1. Temp
a. Solids inc solubility with inc temp
b. Gases dec solubility with inc temp
2. Pressure – gases only – higher pressure = more
soluble
S1 = S2
P1
P2
P 461 practice 1 & 2
Reading solubility curves
a point on the line = saturated solution
a point below the line = unsaturated
a point above the line = supersaturated
Consider a KCl solution at 60oC which 46g of KCl
has been dissolved in 100g of water. The solution is
_____________.
This solution is heated to 80oC. It is now ______
This solution is cooled to 30oC. Either ______ g will
crystallize out, ______g will stay dissolved and the
solution will be __________
OR all 46g will stay dissolved and the solution will
be _________________
Concentration units
1. % by mass – grams solute / grams solute +
solvent
p. 463 #8 - 10
2. Molarity (M) – moles solute per liter of solution
(not just the water)
p. 465 #14 – 16
To find conc when a solution is diluted to
weaker conc;
M conc Vconc = M dil Vdil
p. 468 # 21 – 23
[ NaCl] = molarity of NaCl solution
3. Molality (m)– moles solute / kilograms solvent
p. 469 #24-25
4. Mole fraction– moles solute / moles solute +
moles solvent
p. 470 # 26 27
Colligative Properties – properties that depend only
on number of particles, not what those particles are.
Van’t Hoff factor (i) – number of particles you’ll get
from each formula unit
Molecular compounds/covalent compounds, have
Van’t Hoff = 1 since they dissolve as whole
molecules.
NaCl breaks into 1 ion of Na+ and 1 ion of Cl-NaCl has Van’t Hoff factor = 2
CaCl2 breaks into 1 ion of Ca+2 and 2 ions of Cl-CaCl2 has Van’t Hoff factor = 3
AlI3 breaks into 1 ion of Al+3 and 3 ions of I-AlCl3 i = 4
Al2(SO4)3 breaks into 2 ions of Al+3 and 3 ions of
SO4—2 This ionic compound has Van’t Hoff factor
of 5
What is the Van’t Hoff factor for Na3PO4 ?
i=
What is the Van’t Hoff factor for C6H12O6?
i=
Colligative Properties
1. Vapor pressure – when a nonvolatile solute is
dissolved in a solvent, the vapor pressure is
lowered
Fewer solvent particles on the surface mean less
molecules available to escape into gaseous
phase.
2. Boiling pt elevation – you have to get a
substance hotter to get it to boil when something
is dissolved in it.
Tb = i Kb m
Kb is called boiling pt
elevation constant - characterisitic for each
solvent (see p. 472)
3. Freezing pt depression – freezing pt temp of a
solvent is lowered by presence of solute particles
Tf = i Kf m Kf = freezing pt depression
constant – see p. 474
4. Osmotic pressure – effects diffusion through a
membrane.
Movement is solvent moving from less conc to
more conc solution through membrane.