Chemical Solutions

Question 1

Evaporation

Answer 1

Change of a substance from the liquid phase to the gas phase
If the solvent evaporates, the volume of the solution decreases while the moles of the solute stays the same.
If the solute stays the same and the volume of the solution decreases, the concentration of the solute will increase

Question 2

Decomposition

Answer 2

Involves the breakdown of a compound into two or more substances
If a compound decomposes, its concentration will decrease

Question 3

Precipitation

Answer 3

The formation of an insoluble solid in a solution either as a result of super-saturation or by converting the solute into its insoluble form
When a solute (aq) precipitates out of solution, it becomes a solid, which is not a solute, and therefore the concentration of the solution decreases as the moles of solute decrease

Question 4

Neutralization

Answer 4

Involves the reaction between an acid and a base to form water and a salt
If a compound is an acid or a base and is neutralized by water, the reaction will decrease its concentration

Question 5

Disproportionation

Answer 5

A reaction in which a compound is simultaneously oxidized and reduced, giving two different products
Oxidation and reduction of a compound would decrease the concentration of the compound as it yields a different product

Question 6

Calculating mass percent

Answer 6

Mass percent = grams solute / grams solution x 100%

Question 7

Solubility of a gas increases as:

Answer 7

Temperature of the solution decreases and pressure of the gas increases

Question 8

Colligative properties

Answer 8

Based on the number of solute and solvent particles in a solution not the identity of the particles themselves

freezing point, boiling point, vapor pressure, osmotic pressure are all colligative properties

Question 9

Boiling point elevation formula

Answer 9

• increase in boiling point of a solution
  ΔT_b = i x m x K_b
  ΔT_b: the change in temperature
  i: Van’t Hoff factor
  m: molality
  K_b: boiling point constant

particles measured in molality because it remains constant with temp

Question 10

How is vapor pressure affected when NaCl is added to distilled water?

Answer 10

Vapor pressure decreases: the more solute in the solution, the more the solute completes with the solvent at the surface of the solution. With fewer solvent molecules at the surface, the less solvent can escape the liquid and become a gas and therefore vapor pressure decreases
Raoult’s law: P_solution = M_solvent x P_solvent (Psolution is the vapor pressure, Msolvent is the mole fraction of the solvent, and Psolvent is the vapor pressure of the solvent)

Question 11

Osmotic pressure is directly proportional to:

Answer 11

The molarity of the solute and the temperature of the solution

Question 12

The higher the Van’t Hoff factor, the higher/lower the osmotic pressure if everything else is the same

Answer 12

Higher

Question 13

When a solute is added to a liquid:

Answer 13

Boiling point increases
Vapor pressure decreases
Osmotic pressure increases
Freezing point decreases

Question 14

Increasing the solute concentration in a solution will cause the freezing point to increase/decrease and the vapor pressure to increase/decrease

Answer 14

Adding a solute to solution will depress (lower) the freezing point of the solution and elevate (increase) the boiling point of the solution and thereby decreasing vapor pressure (boiling point and vapor pressure are inversely related)

Question 15

formula for finding osmotic pressure:

Answer 15

π = MiRT
* π = osmotic presure (atm)
* M = molarity
* i = van’t Hoff factor
* R = universal gas constant (0.0821)
* T = temperature (K)

Question 16

for solids in liquids, an increase in temperature ____ solubility

Answer 16

increase

Question 17

for gases in liquids, an increase in temperature ____ solubility

Answer 17

decrease

Question 18

for gases in liquids, an increase in pressure ____ solubility

Answer 18

increases

Question 19

vapor pressure

Answer 19

• pressure exerted by the gaseous phase of a liquid that evaporated from the exposed surface of the

Question 20

describe boiling point of a solution containing dissolved solute in relaiton to entropy:

Answer 20

• a solutions contains dissolved solute, the solute molecules are in a state of high entropy
• this extra entropy makes it more difficult for the solution to boil
• boiling the solution with dissolved solute requires more energy

Question 21

boiling point of a liquid:

Answer 21

• the temperature at which the vapor pressure of the solution is equal to the atmospheric pressure over the solution

Question 22

formula for calculating the new vapor pressure of a solution after solutes have been added:

Answer 22

• Raoult’s law: P_a = (X_a)(P°_a)
• P_a = vapor pressure of a solution with a non-volatile solute
• (X_a) = mole fraction of the solvent
• (P°_a) = pure vapor pressure of the solvent

Question 23

describe how freezing point is affected when solutes are dissolved in a solution?

Answer 23

• when solutes are added, they interfere with the tightly-packed arrangement a substance would normally form when frozen
• the liquid will be less likely to achieve a solid state when a solute is present
• therefore, freezing point will decrease

Question 24

freezing point depression formula:

Answer 24

ΔT_f = i x m x -K_b
ΔT_f: the change in temperature
i: Van’t Hoff factor
m: molality
-K_f: boiling point constant

negative because temperature decreases

Question 25

what does osmotic pressure calculate?

Answer 25

• the pressure it would take to stop osmosis from happening