CHM 2046: Review for Exam 1

Solute

The substance that is dissolved in a solution (e.g., salt in saltwater).

Solvent

The substance that dissolves the solute (e.g., water in saltwater).

Solutions

one compound (solute) is dissolved in another (solvent)

aqueous solution

when the solvent is water

electrolytes

substance which dissolves in water to give an electrically conducting solution

solubility

the amount of a substance that dissolves in a given quantity of solvent

saturated solution

solvent holds as much solute as is possible at that temperature

unsaturated solution

less than the maximum amount of solute for that temperature is dissolved in the solvent

supersaturated solution

solvent holds more solute than is normally possible at that temperature

miscible

when two liquids create a homogenous mixture

immiscible

when two liquids create a heterogeneous mixture

the 4 conditions that determine solubility/miscibility

1) intermolecular forces between the solvent and solute

2) entropy change that accompanies the solvation

3) temperature

4) pressure

Solvation

the process where solute particles (ions or molecules) become surrounded and stabilized by solvent molecules

Henry’s Law

S_g = kP_g

S_g: the solubility of the gas

k: Henry’s law constant for that gas in that solvent

P_g: The partial pressure of the gas above the liquid

percent mass

Mass % of A = (mass of A in solution/ total mass of solution) x 100

mol fraction

X_A = moles of A/ total moles in solution

molarity

M = mol of solute/ L of solution

molality

m = mol of solute/ kg of solvent

Units to express solubility

g/L, mol/L, mol/kg

factors affecting solubility:

o temperature (solids and liquids vs gases)

o pressure (solids vs liquids vs gases); Henry’s law: S(gas) = k x P_g

o molecular size and shape

o polar vs nonpolar (like dissolves like)

grams to moles

moles= mass (grams)/ molar mass (g/mol)

Raoult’s law

P_solvent= X_solvent x P°_solvent

Where, X_solvent is the mole fraction of the solvent and P°_solvent is the normal vapor pressure of pure solvent at that temperature.

Vapor pressure of a solution is ? than that of the pure solvent.

LOWER

Positive and negative deviations, what intermolecular forces leads to each?

For a positive deviation, the vapor pressure for a given mixture is greater than would be expected.

The vapor pressure is lower than would be expected from Raoult’s Law i.e. the intermolecular forces increase when the liquids are mixed. This is generally because molecules where no hydrogen bonding is present are mixed to form a liquid with hydrogen bonds.

Define colligative properties

Properties of solutions that depend only on the NUMBER of solute particles present, not on the identity of the solute particles.

List the 4 colligative properties

• Vapor pressure lowering

• Boiling point elevation

• Melting point depression

• Osmotic pressure

Give formulas for ΔTb and ΔTf

ΔT_b =__

ΔT_f =__

What concentration units are used in the above formulas? C°, molal, and C°/mol

ΔT_b = K_b x m

ΔT_f = K_f x m

Are the ΔT values to be added or subtracted?

Boiling point:_ADDED_

Freezing point:_SUBTRACTED_

Which of the following solutions would not be expected to exist?

Methanol, CH3OH, in water

Does molarity or molality change with temperature?

molarity

Solubility of a gas increases as ? and ? increases, and decreases as ? is increased

pressure and size, temperature

Physical properties that depend on the ? but not the ? of solute particles in a given amount of solvent are called colligative properties.

number ; kind