Physical Properties Physical Properties of Solutionsof Solutions

Chapter 13Chapter 13

8/21/86CO2 Cloud Released

1700 Casualties

Lake Nyos, West AfricaLake Nyos, West Africa

• Earthquake?

• Landslide?

• Wind/Rain?

Chemistry In Action: The Killer LakeLake Nyos, West AfricaLake Nyos, West Africa

Concentration Units

• Mass percentage

• ppm and ppb

• Mole fraction

• Molarity

• Molality

Concentration - amount of solute present in a given quantity of solvent or solution:

Concentration Units

Mass percentage (w/w)

% by mass = x 100%mass of solute

mass of solute + mass of solvent

= x 100% (w/w)mass of solutemass of solution

Mole Fraction (X)

XA = moles of A

sum of moles of all components

Parts per million (ppm)

Parts per billion (ppb)

Concentration Units

610 x soln mass

solute mass ppm

910 x soln mass

solute mass ppm

Concentration Units

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

What is the molality of a solution made by dissolving 36.5 g of naphthalene (C10H8) in 425 g of toluene (C7H8)?

Answer: 0.671 m

Practice Exercise p 544

What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL?

m =moles of solute

mass of solvent (kg)M =

moles of solute

liters of solution

5.86 moles ethanol = 270 g ethanolAssume 1 L of solution:

(0.927 g/mL) (1000 mL) = 927 g of solution

mass of solvent = mass of solution – mass of solute

= 927 g – 270 g = 657 g = 0.657 kg

m =moles of solute

mass of solvent (kg)=

5.86 moles C2H5OH

0.657 kg solvent= 8.92 m

(a) Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water.

(b) A commercial bleaching solution contains 3.62 %(w/w) sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2.50 kg of bleaching solution?

Answer: (a) 2.91%

(b) 90.5 g of NaOCl

Practice Exercise p 543

An aqueous solution of hydrochloric acid contains 36% HCl by mass. Calculate the mole fraction of HCl in the solution.

Sample Exercise 13.6 Calculation of Mole Fraction

Assume we have 100. g of solution:

Conversion of Concentration Units

• If we know the density of the solution, we can calculate the molality from the molarity and vice versa.

Fig 13.19 Calculating molality and molarity