Concentration Units Continued

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

12.3

Solution Stoichiometry

The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

M = molarity =moles of solute

liters of solution

How many moles of KI are required to make 500. mL of a 2.80 M KI solution?

Solution Stoichiometry

The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Another way this can be expressed is in mass percentage.

Mass %=mass of solute

mass of solution

What is the mass percentage of 2 moles of NaOH dissolved in 358 ml of water?

X 100

Solution Stoichiometry

The concentration of a solution can also be expressed as the moles of solute per kg of solvent.

m = molality =moles of solute

kg of solvent

What is the molality of a solution that has contains83.05g of KI dissolved in 500ml of water?

What is the molality of a solution made from 155g of sodium chloride and 1500g of water?

m =moles of solute

mass of solvent (kg)

155g of NaCl = 2.65 mol NaCl 1500g of water = 1.5kg of water

____________________2.65 moles NaCl

1.5kg water = 1.8m

Change in Boiling Point

Common Applications of Boiling Point Elevation

12.6

What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g.

DTf = Kf m

m =moles of solute

mass of solvent (kg)= 2.41 m=

3.202 kg solvent

478 g x 1 mol62.01 g

Kf water = 1.86 0C/m

DTf = Kf m = 1.86 0C/m x 2.41 m = 4.48 0C

DTf = T f – Tf0

Tf = T f – DTf0 = 0.00 0C – 4.48 0C = -4.48 0C

12.6

Colligative Properties of Electrolyte Solutions

12.7

0.1 m NaCl solution 0.1 m Na+ ions & 0.1 m Cl- ions

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

0.1 m NaCl solution 0.2 m ions in solution

van’t Hoff factor (i) = actual number of particles in soln after dissociation

number of formula units initially dissolved in soln

nonelectrolytesNaCl

CaCl2

i should be

12

3

Which chemical below would be bestto de-ice a frozen street and why?

a) sand, SiO2

b) Rock salt, NaCl

c) Ice Melt, CaCl2

Change in Freezing Point

At what temperature will a 5.4 molal solution of NaCl freeze?

Solution

∆TFP = Kf • m • i

∆TFP = (1.86 oC/molal) • 5.4 m • 2

∆TFP = 20. oC

FP = 0 – 20. = -20. oC

Freezing Point Depression

Triple point diagram

solid

liquid

gas

Phase diagram