Module 10

Question 1

Calculate volume percent composition

Answer 1

((volume of component) / (total volume of soln)) * 100%

Question 2

If there’s an impurity in a solution

Answer 2

-add to increase boiling point
(boiling pt elevated)
-substract to decrease freezing point
(freezing pt depressed)

Question 3

Finding freezing/boilling point

Answer 3

Use eqn:
(d)T = Km
m= molality
(d)T = Difference in temperature of boiling/freezing point
K = constant
Then 0 degrees C
+ (d)T if boiling point
- (d)T is freezing point

Question 4

molality

Answer 4

m = moles solute / kg of solvent

Question 5

Osmotic pressure

Answer 5

pressure of a solution required to stop osmosis
pi = MRT
pi = osmotic pressure
M = molarity
R = gas constant (in Kelvin) = 0.08206
T = absolute temperature (Kelvin)
Osmosis should be in atm.

Question 6

Electrolyte solution and particles

Answer 6

Electrolytes dissociate in solution, thus there are more particles in a solution than molecules

Question 7

van’t Hoff factor (i)

Answer 7

i = (# of particles in solution after dissociation) / (number of formula units dissolved in soln)
i = pi / (MRT)
(osmotic pressure eqn^)

Question 8

van’t Hoff factor for nonelectrolytes

Answer 8

1

Question 9

mass/volume percentages are always implied to be?

Answer 9

g/mL

Question 10

When gases are dissolved in a liquid solvent, what can change their solubility?

Answer 10

Higher temperature - solubility decreases
Higher pressure - solubility increases

Question 11

When solids/liquids are dissolved in a liquid solvent, what can change their solubility?

Answer 11

Higher temperature - solubility increases
Higher pressure - n/a

Question 12

mass percent composition eqn

Answer 12

(mass of element / mass of whole molecule) * 100

Question 13

mole fraction eqn

Answer 13

i (mole fraction) = (moles of i) / (total moles)
ALSO:
using delta_Pressure = molefraction_solute * initialP_solvent
molefraction_solute = delta_Pressure / initialP_solvent

Question 14

molality eqn

Answer 14

(moles of solute) / (kg of solvent)
ALSO:
delta_T / constant = molality

Question 15

Freezing point depression

Answer 15

delta T
Tinitial - T_final = delta_T

Question 16

Henry’s Constant

Answer 16

k = c/P
k = Henry’s Constant
c = concentration of solute / 1 atm
P = 1 atm

Question 17

Finding solubility given partial pressure

Answer 17

c = kP
k = Henry’s constant (calculated w/ concentration / 1atm)
P = given pressure

Question 18

Vapor Pressure of Solution

Answer 18

= (mole fraction of solvent) * (original pressure of solvent in mmHg)
Note: mole fraction of solvent = moles of solvent / (moles of solvent + solute)
Note: solvent can be replaced with any other kind of molecule, not just solvent

Question 19

Finding moles of solute w/ mole fraction

Answer 19

n_solute = (mole fraction of solute * moles of solvent) / (1 - mole fraction of solute)

Question 20

Partial pressure

Answer 20

= mole fraction * initial pressure

Question 21

Find freezing/boiling point

Answer 21

1. delta_T = constant * molality
2. add/subtract delta_T from initial boiling/freezing pt

Question 22

moles eqn for an element in a molecule

Answer 22

mol = (% of element) / atomic wright of element

Question 23

Molecular Formula

Answer 23

1. Find empirical formula
2. Divide molecular mass by mass of empirical formula
3. Multiply coefficients of empirical formula by the quotient