1. Chapter 13 and 14 Honors Chemistry
Solutions
Chapter 13 and 14
Honors Chemistry

2. Solution
Definition: a homogeneous mixture of 2 or more substances in a single physical state
Parts: solute and solvent (usually water)

3. Types of solutions Physical states: solid (alloys), liquid, gas
Miscible vs. Immiscible
Miscible - liquids that dissolve freely in one another in any proportion
Immiscible - liquid solutes and solvents that are not soluble
Dilute vs. Concentrated
Electrolyte vs. Nonelectrolyte
Saturated, Unsaturated and Supersaturated

4. Supersaturated Solution demo

5. Electrolyte vs. Nonelectrolyte

6. Saturated – soln containing the max amt of solute
Unsaturated – soln containing less solute than a sat soln under the existing conditions
Supersaturated – contains more dissolved solute than a saturated solution under the same conditions
Solubility Curves

7. supersaturated solution (stirred)

8. Solubility (physical change)
Definition: mass of solute needed to make a saturated solution at a given temperature
solution equilibrium in a closed system
dissolution ↔ crystallization
Unit = g solute/100 g H2O

9. What is the solubility at 70oC?
At 20oC, a saturated solution contains how many grams of NaNO3 in 100 g of water?
Saturated sol’n
90 g
What is the solubility at 70oC?
Supersaturated solution
135 g/100 g water
What kind of solution is formed when 90 g NaNO3 is dissolved in 100 g water at 30oC?
Unsaturated solution
unsaturated
What kind of solution is formed when 120 g NaNO3 is dissolved in 100 g water at 40oC?
supersaturated

10. Solubility of solids in liquids
For most solids, increasing temperature, increases solubility.
In general, “like dissolves like”. Depends on
Type of bonding
Polarity of molecule
Intermolecular forces between solute and solvent

11. Solubility of Gases
Gases are less soluble at high temperatures than at low temperatures
Increasing temperature, decreases solubility.
Increasing pressure, increases solubility.

12. The quantity of gas that dissolves in a certain volume of liquid is directly proportional to the pressure of the gas (above the solution).

13. Effervescence – rapid escape of gas dissolved in liquid

14. Factors Affecting Solubility
Increase surface area of solute (crushing)
Stir/shake
Increase temperature

15. Dissolution Process Ionic Compounds NaCl(s)  Na+1(aq) + Cl-1(aq)
For dissolution to occur, must overcome solute attractions and solvent attractions.
Dissociation Reaction: the separation of IONS when an ionic compound dissolves (ions already present)
Try calcium chloride
electrolyte
nonelectrolyte
Dissolving NaCl in water
hexahydrated for Na+1;
most cations have 4-9 H2O molecules
6 is most common
Solvation: process of solvent molecules
surrounding solute
Hydration: solvation with water

17. Dissolution Process Molecular Compounds
Nonpolar molecular solids do not dissolve in polar solvents
naphthalene
Polar molecule
C12H22O11(s)  C12H22O11(aq)
Molecular solvation
Nonelectrolyte
HCl(g)  H+1(aq) + Cl-1(aq) or
HCl(g) + H2O  H3O+1(aq) + Cl-1(aq)
Ionization: ions formed from solute molecules by action of solvent (no ions initially present)
Nonelectrolyte (HCl)  electrolyte (ions)

18. Energy Changes Heat of solution = Hsoln Endothermic Exothermic
Solute particles separating in solid
Solvent particles moving apart to allow solute to enter liquid
Energy absorbed
Exothermic
Solvent particles attracted to solvating solute particles
Energy released
Hsoln = heat of solvation –
crystal lattice energy

19. Solution Reactions Single replacement Double replacement
Activity Series
Double replacement
Solubility chart (soluble vs. insoluble)
Neutralization (water)
Gases (CO2 and H2S)

20. Concentration Percent concentration by mass (mass %) Molarity (M)
(solute/solution) x 100% = % Concentration
Molarity (M)
Moles of solute/Liters of solution = mol/L
Molality (m)
Moles of solute/mass of solvent = mol/kg
ppm and ppb
Used for very dilute solutions
Dilution – a process in which more solvent is added to a solution
How is this solution different?
Volume, color, molarity
How is it the same?
Same mass of solute, same moles of solute
In Dilution ONLY: M1V1 = M2V2

21. Colligative Properties
Definition: physical properties of solutions that differ from properties of its solvent.
Property depends upon the number of solute particles in solution.
Types:
Vapor Pressure
Boiling Point ELEVATION
Freezing Point DEPRESSION

22. Vapor Pressure A measure of the tendency of molecules to escape from a liquid
For nonvolatile liquids or solid solutes
A nonvolatile solute will typically increase the boiling point and decrease the freezing point.
Adding a nonvolatile solute lowers the concentration of water molecules at the surface of the liquid.
This lowers the tendency of the water molecules to leave the solution and enter the gas phase.
Therefore the vapor pressure of the solution is LESS than pure water.

23. Same Temperature H2O H2O Sugar H2O Temperature (ºC)
Vapor Pressure (kPa)
100 40 20 60 80
H2O
solution

24. Boiling Point Elevation
tb = boiling point elevation
tb = iKbm
i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process)
Kb = molal bp elevation constant
Kb = 0.512°C·kg H2O
moles of solute (ions or molecules)
m = molality = moles solute
kg of solvent
bp of solution = bp of solvent + tb

25. Boiling Point Elevation and Freezing Point Problems
At what temperature will a solution begin to boil if it is composed of 1.50 g potassium nitrate in 35.0 g of water?
Solute:
At what temperature will a solution begin to freeze when 18.0 g ammonium phosphate is dissolved in g water?

26. Freezing Point Depression when a solution freezes, the solvent solidifies as a pure substance; deviates for more concentrated solutions
tf = freezing point depression
tf = iKfm
i = molality conversion factor; for electrolytes adjust for # of ions actually present in solution (dissociation process)
Kf = molal freezing point depression constant
Kf = 1.858°C·kg H2O
moles of solute (ions or molecules)
m = molality = moles solute
kg of solvent
fp of solution = fp of solvent - tf

27. Osmotic Pressure The external pressure needed to stop osmosis
Osmosis is the movement of solvent through a semi permeable membrane from lower concentration to higher concentration

28. the pressure required to allow for no transport of solvent across the membrane is called the OSMOTIC pressure