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

intermolecular forces, entropy change, temperature, pressure

Solvation

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

What does each variable mean in 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; Pg: 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

XA = 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:

temperature, pressure, Henry’s law, molecular size and shape, polarity

grams to moles

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

What does each variable mean in Raoult’s law: P_solvent= X_solvent x P°_solvent

Where, Xsolvent is the mole fraction of the solvent and P0solvent 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 is greater than expected.

For a negative deviation, the vapor pressure is lower than would be expected

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?

DTb = Kb x m; DTf = Kf x m; C, molal, and C/mol

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?

NaCl in water

MgCl2 in CCl4

Methanol, CH3OH, in water

Pentane, CsH12, in CCl4

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

Which of these aqueous solutions would be expected to have the lowest freezing point energy?

0.100 m KCl

0.200 m CH3OH

0.100 m NaOH

0.075 m K2SO4

0.075 m K2SO4

The Tyndall effect describes ?

the scattering of light by colloidal particles

Which one of the following statements about soaps and soap molecules is false?

• They are often sodium salts of long chain fatty acids.

• The hydrophilic end of a soap molecule is attracted by grease.

• They have a hydrophobic end.

• They have a polar end.

The hydrophilic end of a soap molecule is attracted by grease.

Which statement is incorrect?

• The Law of Conservation of Energy is another statement of the First Law of Thermodynamics.

• The energy of the universe is constantly increasing.

• Energy is the capacity to do work or to transfer heat.

• Potential energy is the energy that a system possesses by virtue of its position or composition.

The energy of the universe is constantly increasing.

Which term is not correctly matched?

• universe / system plus surroundings

• exothermic / energy is released

• endothermic / energy is absorbed

• state function / property dependent on how the process takes place

state function / property dependent on how the process takes place

Which statement concerning sign conventions for DE = q + w is false?

• For heat absorbed by the system, q is positive.

• For work done by the system, w is negative.

• When energy is released by the reacting system, DE is negative.

• If DE is positive, products are at a lower energy than reactants.

If DE is positive, products are at a lower energy than reactants.

Lattice Energy

how much energy you need to break a bond

hydration energy

Energy released when water molecules surround ions, like salt, as they dissolve

State Raoult’s law and the equation: P(solution) = ________*_________

The vapor pressure of a solvent in an ideal solution is directly proportional to its mole fraction in the solution. Xsolvent x P0solvent

vapor pressure ? as temperature increases, and ? as the strength of the intermolecular forces increases.

increases; decreases

as vapor pressure increases, boiling point ?

decreases

For an ideal mixture of 2 liquids, the total vapor pressure in terms of the mol fractions and partial pressures is expressed as

XA x P0A + XB x P0B

A positive deviation from Raoult’s law implies that

o the vapor pressure of the solution is ? than predicted by ideal

behavior

o the boiling point of the solution is ? than predicted by ideal behavior

o the intermolecular forces in the solution is ? than that of the

individual solvents.

greater; lower; weaker

A negative deviation from Raoult’s law implies that

o the vapor pressure of the solution is ? than predicted by ideal

behavior

o the boiling point of the solution is ? than predicted by ideal behavior

o the intermolecular forces in the solution is ? than that of the

individual solvents.

lower; higher; stronger