Physical Properties Physical Properties of Solutionsof Solutions

Chapter 13Chapter 13

Factors Affecting Solubility

• Glucose (which has hydrogen bonding) is very soluble in water

• Cyclohexane (which only has dispersion forces) is not

Fig 13.12 Structure and solubility

Pressure Effect on Gases in Solution

• Solubility of liquids and solids does not change appreciably with pressure

• Solubility of a gas in a liquid is directly proportional to its pressure

Fig 13.14 Effect of pressure on gas solubility

Henry’s Law

Sg = kPg

where

• Sg ≡ solubility of the gas

• k ≡ the Henry’s Law constant for that gas in that solvent

• Pg ≡ partial pressure of the gas above the liquid

Fig 13.15 Solubility decreasesas pressure decreases

Temperature Effect on Solids and Liquids

• Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature

Fig 13.17 Solubilities of several ion compoundsas a function of temperature

• The opposite is true of gases:

• Carbonated soft drinks are more “bubbly” if stored in the refrigerator

• Warm lakes have less O2 dissolved in them than cool lakes

Temperature Effect on Gases

Fig 13.18 Variation of gas solubility with temperature

Concentration Units

• Mass percentage

• Mole fraction

• ppm and ppb

• 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

(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 mass % 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:

Parts per million (ppm)

Parts per billion (ppb)

Concentration Units Continued

610 x soln L

solute moles ppm

910 x soln L

solute moles ppm

Concentration Units Continued

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: 0.670 m

Practice Exercise p 544

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

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

Assume 1 L of solution:5.86 moles ethanol = 270 g ethanol927 g of solution (1000 mL) (0.927 g/mL)

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