Chapter 8 Solutions

A. Definition

• A solution is a homogeneous mixture of two or more different substances • only one phase• composition is variable• almost always clear (transparent)• A solution cannot be separated into its components by filtration

Solute – dissolved substance (smaller amount)Solvent – dissolving medium (larger amount)

Solutions can be in gas, liquid or solid phases

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B. Types of solutions a) Solid – liquid

1. Ionic compoundNaCl in water NaCl Na+ + Cl- breaking of ionic bond

H2O

Hydration

Ion-dipole attraction

2

2. Covalent compounds

sugar in water

O OH

OH

OH

HO

HOH2C

H

O

H

H

O

H

H

O

H

HO

H 3

b. Liquid - liquid

C O H and H2O

H

H

H

(CH3OH)

Polar polar

H O

CH3

H O

H

H O

CH3

Polar dissolves in polarNonpolar dissolves in nopolar

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c. Gas – liquid All gases are slightly soluble in water

d. Gas-gas All mixtures of gases are solutions

e. Solid – solidCu (copper) in Au (gold) Alloy

Brass (Cu/Zn)

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C. SolubilitySoluble – dissolves a large amountInsoluble – dissolves an negligible amount

Miscible – both components are liquid and can dissolve (mix) in any proportion

example: H2O and CH3OH

a) Solubility - # of grams that can be dissolved in 100 g of solvent at saturation (equilibrium)

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Figure 8.3 In a saturated solution, the dissolved solute is in equilibrium with the undissolved solute.

Example:7

Table 8.1 Solubilities of Various Compounds in Water at 0oC, 50oC, and 100oC.

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Unsaturated solution – dissolved amount less than solubility

Supersaturated solution - dissolved amount more than

solubilityAqueous solution – solution in water

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D. Factors affecting solubility 1. Nature of solute and solvent

In general, for non-ionic solutes, “like dissolves like’.

• polar solutes dissolve in polar solvents. • nonpolar solutes dissolve in nonpolar solvents.

Ionic compounds do not dissolve in nonpolar solvents

CH4 in water? NaCl in octane (nonploar)?

CH4OH in water?

HCl in water?

Examples

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Solubility Guidelines for common Ionic Compounds in Water.

1. All compounds containing group IA (Li+, Na+, K+, etc.) and NH4

+ are soluble in water.

2. All nitrates (NO3-) and acetates (CH3COO- or C2H3O-)

are soluble in water.

3. All chlorides (Cl-), bromides (Br-) and iodides (I-) are soluble in water except those of Ag+, Pb2+ and Hg2

2+.

4. All sulfates (SO42-) are soluble except

PbSO4, BaSO4, SrSO4 and CaSO4

5. All hydroxides (OH-) are insoluble except those of IA & Ca(OH)2, Sr(OH)2, Ba(OH)2

6. Most other ionic compounds are insoluble in water11

Li+, Na+, K+ and NH4+ soluble

NO3-, CH3COO- soluble

Cl- , Br-, I- soluble AgX, PbX2, Hg2X2.SO4

2- soluble PbSO4, BaSO4,CaSO4, SrSO4

OH- insoluble IA, Ca2+, Sr2+, Ba2+

Solubility except

K2SO4

NaCl

PbCl2

MgSO4

Soluble in water?

CaCO3

Fe(NO3)2

NH4MnO4

Soluble in water?

BaSO4

CuCr2O7

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Which of the following would be expected to be the most soluble in water?

C C C

H

H

H

H

H

H

H

H

C C C

H

H

H

H

H

H

O

H

C C C

H

H

H

H

H

H

C

H

O

H

H

H

H

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2. TemperatureGenerally, solubility increases as T increases, except for most gases in liquid where solubility decreases as T increases.

Example: O2 in water

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3. Pressure (above the surface of the solution) Only affects solubility of gases in liquid.

Solubility increase as P increases.

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E. Concentrations of solutions - amount of solute in certain amount of solvent or solution.

a) % by mass (mass-mass %)

b) % by volume (V-V %)

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Figure 8.7 When volumes of two different liquids are combined, the volumes are not additive.

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Figure 8.8

Identical volumetric flasks are filled to the 50.0-mL mark with ethanol and

with water.

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c) mass-volume %

d) parts per million (ppm)

e) parts per billion (ppb)

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If an aqueous solution is 2.5 % w/v in aluminum sulfate, Al2(SO4)3, how many grams of aluminum sulfate are there in a liter of solution?

Examples

How many grams of zinc fluoride, ZnF2, are required to make a 5.00 % w/v aqueous solution in a 250 mL volumetric flask?

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e) Molarity, M (molar concentration)

# of moles of solute/liters of solution

Example 10.50 mol KOH is dissolved in 2.0L of solution. Find the molarity.

1L

NaCl

1 mole NaCl

1 M NaClsolution

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Example 2How many grams of NaCl is needed to make 250 mL of a 0.50 M NaCl solution?

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Example 3. Make a 500mL of 0.250 M K2Cr2O7 solution

MW of K2Cr2O7 = 294.2

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F. Dilution

)(literV

nM or MV = n

In general, C1V1 = C2V2, where C stands for concentration

M1V1 = M2V2

M2V2

M1V1

addwater

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M1V1 = M2V2

Example 1. A 250 mL 2.0M NaOH solution is diluted to 1.0 L. What is the molarity of the final solution?

Example 2. What volume of a 5.0M HCl solution would be needed to prepare 2.0 L of a 0.25M HCl solution?

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G. Colligative properties of solutions

A colligative property is a physical property of a solutionthat depends only on the concentration.

a) Lowering of vapor pressure

water

Next day

sugar in water

water

sugar in water

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water

sugar in water

b) Elevation of the Boiling point

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c) Freezing point (depression) lowering

Example: Antifreeze; salt-water.

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H2O solution

Semi-permeable membrane

d) Osmosis and Osmotic pressure

Osmosis: the flow of solvent through a semipermeable membrane from a dilute to a more concentrated solution.At equilibrium, the molecules move back and forth at equal rates.

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H2O solution

This measures the osmoticpressure of the solution

The process is called osmosisPressure applied to prevent osmosis = osmotic pressure

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Figure 8.15Osmotic pressure is the amount of pressure needed to prevent the solution in the tube from rising as a result of the process of osmosis.

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V.P. lowering, B.P. elevation and F.P depression and osmotic pressure depend on the concentration of the solute particles but not on the type of solute.

Examples:

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Example:

1.5 mol of K2CrO4 is dissolved in 1000 g of water. What is the freezing point of the solution?

Freezing point (depression) lowering

mol of particle =

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Osmolarity

NaCl Na+ + Cl-

1M NaCl 2 mol ions osmolarity = 2M

osmolarity = M x i

i = # of particles produced from the dissociation of one formula unit of solute

H2O

Osmolarity in cell = 0.31M (osmol)Osmolarity = 0.31M isotonic solution 5.0% m/v glucose 0.92% m/v NaCl (physiological saline solution) 35

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Osmolarity = 0.31M isotonic solution

Osmolarity > 0.31M hypertonic solution

Osmolarity < 0.31M hypotonic solution

cell

crenation

Burst(hemolysis)

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Red blood cell in

a) isotonic solution b) Hypertonic solution c) Hypotonic solution

crenation hemolysis

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Example Consider the following solutions

1M sugar 2M NaCl 1.5M Na2SO4 1M Ca(NO3)2

solution

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H. Colloidal dispersions A colloidal dispersion is a mixture in which a material is dispersed rather than dissolved.

. . . .. . . .

. . . .. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

dispersed phase

Dispersing medium

10-7 – 10-5cm

Cannot be filtered

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Some proteins have size colloidal dispersion

solution colloidal dispersion

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I. Dialysis

Dialyzing membrane - has pores large enough to allow some ions and small molecules to pass along with water and gases.

Kidney cells, blood capillaries, intestinal walls, etc. function as dialyzing membranes.

Dialysis - the movement of ions and small molecules (urea), including water (solvent), across a dialyzing membrane.

Large molecules such as proteins cannot pass through a dialyzing membrane.

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Figure 8.18 In dialysis, there is a net movement of ions from a region of higher concentration to a region of lower concentration. (a) Before dialysis. (b) After

dialysis.

Figure 8.18 In dialysis, there is a net movement of ions from a regionof higher concentration to a region of lower concentration.(a) Before dialysis. (b) After dialysis

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Figure 8.19 Impurities (ions) can be removed from a solution by using a dialysis procedure.

Impurities (ions) can be removed from a solution byusing a dialysis procedure.

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Artificial kidney: a Hemodialysis Machine

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