Ch. 9: Solutions

Question 1

Define solvation.

Answer 1

The electrostatic interaction between solute and solvent molecules. It involved the breaking of interactions between solvent molecules and between solute interactions and forming new intermolecular interactions between the solute and solvent.

Question 2

Is solvation endothermic or exothermic when new interactions are stronger than the original ones?

Answer 2

Exothermic. This process is favored at low temperatures.

Question 3

Is solvation endothermic or exothermic when new interactions are weaker than the original ones?

Answer 3

Endothermic. This process is favored at high temperatures.

Question 4

What is an ideal solution?

Answer 4

When the overall strength of the new interaction is approximately equal to the strength of the original interactions. Thus, the overall enthalpy is zero.

Question 5

How does entropy change upon dissolution?

Answer 5

Increases

Question 6

Define solubility.

Answer 6

The maximum amount of a substance that can be dissolved in a particular solvent at a given temperature. When the maximum amount is added, the dissolved solute is in equilibrium.

Question 7

Are group 1 metals and nitrate salts soluble or insoluble?

Answer 7

They are soluble!

Nitrate = NO3 -

Question 8

What is the difference between molarity, molality, and normality?

Answer 8

molarity = moles of solute / L of solution
molality = moles of solute / kg solvent
normality = molarity x n = equivalents / L of solution

Question 9

What equation is used to calculate the concentration of a solution after dilution?

Answer 9

M₁V₁=M₂V₂

Question 10

Define the saturation point of a solution.

Answer 10

The saturation point is equilibrium. This is when the solute concentration is at its maximum value.

Question 11

How does Ksp change for gas and non-gas solutes?

Answer 11

Non-gas: An increase in temperature will increase Ksp

Gas: An increase in temperature will decrease Ksp because more particles will escape to the gas phase.

Question 12

What is the ion product of a salt?

Answer 12

Analogous to Q, it is the concentrations of the ionic constituents at that given moment in time.

Question 13

What does it mean when IP < Ksp?

Answer 13

The solution is unsaturated and the solute will continue to dissolve

Question 14

What does it mean when IP > Ksp?

Answer 14

The solution is saturated and precipitation will occur

Question 15

What does it mean when IP = Ksp?

Answer 15

The solution is saturated and thus at equilibrium. The rate of the forward and reverse reactions are equal.

Question 16

Why do ion complexes have a high Ksp?

Answer 16

The complexes have multiple polar bonds that allow for dipole-dipole interactions to occur, which stabilizes the dissolution of the complex ion.

Question 17

What is the common ion effect?

Answer 17

Reduced molar solubility of a salt when it is dissolved in a solution that already contains one of its constituent ions as compared to its solubility in a pure solvent.

Question 18

How is the common ion effect explained by Le Chatelier’s principle?

Answer 18

When a solution already contains one of the ions from the products side of the reaction, the system will shift toward the left side, reforming the solid salt. This results in reduced molar solubility and less solid is dissolved in the solution.

Question 19

How does the common ion effect change Ksp?

Answer 19

It doesn’t! Ksp stays the same because Ksp is an inherent property that doesn’t take into account other ions in a solution. The common ion effect changes IP not Ksp.

Question 20

What are colligative properties? Examples?

Answer 20

Physical properties of solutions that depend on the concentration of dissolved particles but not on the chemical identity of the solution.

Ex. vapor pressure depression, BP elevation, FP depression, and osmotic pressure

Question 21

What is Raoult’s Law? What does it account for?

Answer 21

It accounts for vapor pressure depression. As solute is added to a solvent, the vapor pressure of the SOLVENT decreases proportionately. The solute molecules added block the evaporation of solvent molecules but not their condensation.

Question 22

What is Raoult’s Law equation?

Answer 22

Pₐ = XₐPₐ°

Pₐ is vapor pressure of solvent a when solutes are present
Xₐ is the mole fraction of solvent A in the solution
Pₐ° is the vapor pressure of solvent A in its pure state

Question 23

How are BP elevation and VP depression related?

Answer 23

As VP decreases, more energy is needed to evaporate the solute in order for the vapor pressure to equal ambient pressure. Therefore BP rises.

Question 24

What is the change in BP elevation equation?

Answer 24

ΔTb = i(Kb)m

ΔTb is the increase in BP
i is the van’t Hoff factor
(Kb) = constant
m = molality of the solution (mol/kg solvent)

Question 25

What is the density of water?

Answer 25

1 kg/ L = 1 g/mL = 1000 kg/m3

Question 26

What’s the logic behind freezing point depression?

Answer 26

The solutes in the solvent prevent lattice formation due to blocking the interaction between solvent molecules. Energy needs to be removed so that the solvent molecules move slower and are able to find each other to form a lattice. Removing energy decreases the temperature, therefore the freezing point decreases.

Question 27

Define osmotic pressure.

Answer 27

It is a “sucking” pressure generated by solutions in which water is drawn into a solution.

Question 28

What is the osmotic pressure equation?

Answer 28

π = iMRT

i = van't Hoff factor
M = molarity
R = ideal gas constant
T = temperature