Transcript chapter10 - AlvarezHChem

William L Masterton
Cecile N. Hurley
http://academic.cengage.com/chemistry/masterton
Chapter 10
Solutions
Edward J. Neth • University of Connecticut
Concentration Units
General Vocabulary:
Solution – homogeneous mixture of solute and solvent
Solute – the substance being dissolved
Solvent – the substance doing the dissolving
Electrolyte – a substance that conducts electricity
when in solution - ionic
Nonelectrolyte – a substance that does NOT conduct
electricity when in solution - molecular
Concentration Units
• Molarity – (M) moles of solute per liter of solution
• Molarity = moles of solute/liters of solution
Example: What is the molarity of a solution made by
dissolving 12.5g of oxalic acid (H2C2O4) in 456mL
of solution?
Dilution of Solutions
M1V1 = M2V2
Example 10.1
Mass Percent
• Percent by mass = (mass solute/mass solution) * 100
Molality
• the number of moles of solute per kilogram of
solvent
Molality (m) = moles of solute/kilograms of solvent
Example
Conversions Between Concentration Units
Start with a fixed amount of solution or solvent, see right
column
When the original
concentration is
Choose
Mass percent
100 g solution
Molarity (M)
1.00 L solution
Molality (m)
1.00 kg solvent
Example:
Principles of Solubility
• Factors that determine the extent to which a solute
dissolves in a particular solvent:
1. The nature of solvent and solute particles and the
interaction between them
2. The temperature at which the solution forms
3. The pressure, in cases of gaseous solutes
Solute-Solvent Interactions
• “Like dissolves like” = see table in notes
• Polar solutes dissolve in polar solvents
• Nonpolar solutes dissolve in nonpolar solvents
• Nonpolar substances have poor affinity for water
• Petroleum
• Hydrocarbons (pentane, C5H12)
• Polar substances dissolve easily in water
• Alcohols, CH3OH
• Solubility of alcohols decreases as the molar
mass of the alcohol increases
Solubility and Intermolecular Forces
Effect of Temperature on Solubility
An increase in temperature always shifts the
position of an equilibrium to favor an
endothermic process
heat of solution > 0
heat of solution < 0
Figure 10.4 (Solubility Curves – pg 12)
Effect of pressure on Solubility
• Pressure has a major effect on the solubility of a gas
in a liquid, but little effect on other systems
• Henry’s Law - At low to moderate pressure, the
concentration of a gas increases with the pressure
Solubility Effects of Pressure
Colligative Properties of Nonelectrolytes
• The properties of a solution may differ considerably
from those of the pure solvent
• Some of these properties depend on the
concentration of dissolved particles and not on their
nature
Boiling and Freezing Point
• Boiling point elevation and freezing point lowering are both
colligative properties
T f  mK f
Tb  mKb
• Kf is the freezing point lowering constant
• Kb is the boiling point elevation constant
FPL and BPE Constants for Water
• For water,
• Kf = 1.86
• Kb= 0.52
Example 10.7
Molal Constants
Determination of Molar Masses from Colligative
Properties
molality = moles of solute/kg of solvent
MMsolute = grams/moles
Example 10.9
Colligative Properties of Electrolytes
When an electrolyte dissolves it breaks apart into ions.
NaCl(s)  Na+1(aq)
+ Cl-1(aq)
So for every NaCl formula unit 2 aqueous ions are
formed
The formula is adjusted to reflect the number of ions:
∆T = k m i
i = the number of ions formed
Example 10.10
Solution Stoichiometry
Example
Solution Stoichiometry
Example