Properties and Effects of Solutions: Chemistry Solutions, Vapor Pressure, Colligative Properties

Molarity

Molarity = moles of solute / liters of solution

Mass Percent

Mass percent = (mass of solute / mass of solution) × 100

Mole Fraction

Mole fraction of component A (xA) = nA / (nA + nB)

Molality

Molality = moles of solute / kg of solvent

Normality

Normality = equivalents of solute / liters of solution

Equivalents of acids and bases

Mass that donates or accepts a mole of protons

Equivalents of oxidizing and reducing agents

Mass that provides or accepts a mole of electrons

Like Dissolves Like

Polar molecules and ionic compounds tend to dissolve in polar solvents; nonpolar molecules dissolve in nonpolar compounds.

Steps of Solution Formation

1. Breaking up the solute into individual components (endothermic). 2. Overcoming intermolecular forces in the solvent (endothermic). 3. Allowing the solute and solvent to interact to form the solution (often exothermic).

Enthalpy (Heat) of Solution

ΔHsol'n may have a positive sign or a negative sign.

Enthalpy (Heat) of Hydration

Includes ΔH of step 2 and step 3.

Factors Favoring the Solution Process

1. Negative value for ΔHsol'n. 2. Increase in entropy. 3. For positive values of ΔHsol'n, the increase in entropy outweighs the increase in energy.

Structure Effects

Polar (hydrophilic) dissolves in polar; nonpolar (hydrophobic) dissolves in nonpolar.

Henry's Law

The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

Henry's Law Equation

P = kC, where P = partial pressure of the gaseous solute, C = concentration of the dissolved gas, k = constant characteristic of a particular solution.

Temperature Effects on Solids

Increases in temperature usually increase solubility (the amount that can be dissolved).

Temperature Effects on Gases

Solubility of gases always decreases with increasing temperature.

Nonvolatile Solutes

Nonvolatile electrolytes lower the vapor pressure of a solute.

Raoult's Law

Psolvent = P0solvent × Xsolvent, where Xsolvent is the mole fraction of the solvent in the solution.

Ionic Solutes

Dissociation of ionic compounds has nearly two, three or more times the vapor pressure lowering of nonionic (nonelectrolyte) solutes.

Non-ideal Solutions

Liquid-liquid solutions in which both components are volatile.

Modified Raoult's Law

Ptotal = PA + PB, where PA and PB are the partial pressures.

Ideal Solutions

Liquid-liquid solution that obeys Raoult's law; no solution is perfectly ideal, though some are close.

Negative deviations from Raoult's law

Lower than predicted vapor pressure for the solution.

Positive deviations from Raoult's law

Higher than predicted vapor pressure for the solution.

Colligative Properties

Properties dependent on the number of solute particles but not on their identity.

Boiling-Point elevation

Nonvolatile solutes elevate the boiling point of the solvent.

Freezing-Point depression

Solutes depress the freezing point of the solvent.

Osmotic Pressure

The pressure necessary to keep water from flowing across a semipermeable membrane.

Osmosis

The flow of solvent molecules into a solution through a semipermeable membrane.

Dialysis

Transfer of solvent molecules as well as small solute molecules and ions.

Isotonic Solutions

Solutions that have the same osmotic pressure.

Crenation

Cells placed in a hypertonic solution lose water to the solution, and shrink.

Hemolysis

Cells placed in a hypotonic solution gain water from the solution and swell, possibly bursting.

Reverse Osmosis

External pressure applied to a solution can cause water to leave the solution.

van't Hoff factor i

The number of particles in solution divided by the number of moles of dissolved solute.

Expected value of i for NaCl

i = 2.

Expected value of i for BaCl2

i = 3.

Expected value of i for Al2(SO4)3

i = 5.

Actual values of i

Values of i are less than expected due to ion pairing (clustering).

Boiling-elevation and freezing-point depression formula

∆T = imK.

Osmotic pressure formula

π = iMRT.

Colloidal Dispersions (Colloids)

Tiny particles suspended in some medium.

Tyndall Effect

Scattering of light by particles.

Size range of colloidal particles

Particles range in size from 1 to 1000 nm.

Aerosol

Gas dispersing medium with liquid dispersed substance.

Foam

Liquid dispersing medium with gas dispersed substance.

Emulsion

Liquid dispersing medium with liquid dispersed substance.