Chapter 6

Solutions and Colloids

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A solution is a homogenous mixture of 2 or more substances

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

Solution Solvent Solute

Soft drink (l)

Air (g)

Soft Solder (s)

H2O

N2

Pb

Sugar, CO2

O2, Ar, CH4

Snaqueous solutions of KMnO4

Solutions

• Solvents are typically liquids, but can also be gases and (less commonly) solids.

• Solutes are typically solids, gases, and other liquids.

• Table 6.1 page 179

Distinguishing Characteristics

• Homogenous Mixture• Will not separate with time• Cannot separate by filtration• Can have different concentrations• Transparent• Separated into pure components

Solubility

• Solubility is a description of the amount of solute that is dissolved in a certain amount of solvent.

• When two liquids are soluble, they are miscible• Solubility depends on:– Type of solute– Type of solvent– Solute-solvent interactions– Temperature,– The presence of other solutes or contaminants.

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“like dissolves like”

Two substances with similar intermolecular forces are likely to be soluble in each other.

• non-polar molecules are soluble in non-polar solvents

CCl4 in C6H6

• polar molecules are soluble in polar solvents

C2H5OH in H2O

• ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)

Solubility and Solutions

• Solutions have varying degrees of saturation:– Unsaturated solution

– Saturated solution

– Supersaturated solution

Unsaturated Solutions

• Unsaturated solution – Has less than the maximum amount of solute in

solvent.

–More solute can be dissolved in an unsaturated solution.

Saturated Solutions

• Saturated solution;– Has the maximum amount of solute in solvent.

– No more solute can be dissolved in a saturated solution

Supersaturated solution

• Supersaturated solution: – Has more than the maximum amount of solute in

solvent.

– It is highly unstable and solute usually settles out of the solution in order to lower its saturation.

Solubility and Temperature

• Solubility depends on temperature. • For solid solutes, the solubility increases as

temperature increases. More sugar will dissolve in a hot drink than in a cold drink.

• For gas solutes, the solubility decreases as temperature increases. This is why carbonated beverages will fizz more if the drink is warm. This also explains the environmental impact of global warming and thermal pollution to bodies of water.

Gas Solutes

• Solubility of a gas solute also depends on the vapor pressure of the gas above the liquid.

• Henry’s Law – Higher pressures lead to higher solubility– Lower pressures lead to lower solubility. This

explains why carbonated beverages lose their carbonation after they are opened.

–When the bottle is opened, the gas above the liquid is now at atmospheric pressure, a lower pressure.

Concentration

• Concentration is the specific amount of solute dissolved in a solution.

• We will learn four ways to express the concentration of a solution

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Preparing a Solution of Known Concentration

Mass Percent

• Mass percent (percent mass or percent weight) (% m/m or % w/w) is the mass of a solute per total mass of solution. – mass of solution = mass of solute + mass of

solvent.

Volume Percent

• Volume percent (% v/v) is the volume of solute per total volume of solution. (Give equation.)

Mass-Volume Percent

• Mass-volume percent (percent weight by volume or percent mass by volume) (% m/v or %w/v) is the mass of a solute per total volume of solution.

• Problem 6.1 page 185

• Problem 6.2 page 186

Molarity

• Molarity (M) is the number of moles of solute per liters of solution.

M = mol/V

Conversion Factor

• Molarity can be used as a conversion factor, just like the percent concentrations.

• Write the conversion factors from:– 1.85 M HCl– 0.72 M KBr

• Problem 6.3 page 187• Problem 6.4 page 187• Problem 6.5 page 188• Problem 6.6 page 188

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Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.

Dilution

Add Solvent

Moles of solutebefore dilution (i)

Moles of soluteafter dilution (f)=

MiVi MfVf=

Dilution

• Dilution is the process of decreasing the concentration of a solution by adding more solvent.

• The equation for dilution calculations is: C1V1 = C2V2

– where C can be any concentration (molarity) as well as percent concentrations.

• Problem 6.7 and 6.8 page 189

Parts per Million• Exactly like % (parts per 100)• Write out 1 ppm• Write out 1 ppb (parts per billion)• Problem 6.9 page 191

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Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.

H2O

Solvated is a term used for all solvents

Hydrates

• Water molecules in a crystalline solid• Anhydrous: The crystal withou water– CaSO4 H∙ 2O

• Hygroscopic: Crystals that become hydrated from the air

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A solution is a homogenous mixture of 2 or more substances

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

Solution Solvent Solute

Soft drink (l)

Air (g)

Soft Solder (s)

H2O

N2

Pb

Sugar, CO2

O2, Ar, CH4

Snaqueous solutions of KMnO4

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Nonelectrolyte does not conduct electricity?

No cations (+) and anions (-) in solution

C6H12O6 (s) C6H12O6 (aq)H2O

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Water will dissolve covalent compountds

Notice the solutions become ionic. Why is that important for our bodies?

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Hydronium ion, hydrated proton, H3O+

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A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.

Colloid versus solution

• collodial particles are much larger than solute molecules

• collodial suspension is not as homogeneous as a solution

• colloids exhibit the Tyndall effect

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Colligative Properties of Nonelectrolyte Solutions

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

Boiling-Point Elevation Tb = Kb m

Freezing-Point Depression Tf = Kf m

Osmotic Pressure () = MRT

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Colligative Properties of Electrolyte Solutions

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

nonelectrolytesNaClCaCl2

i should be

123

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Boiling-Point Elevation Tb = i Kb m

Freezing-Point Depression Tf = i Kf m

Osmotic Pressure () = iMRT

Colligative Properties of Electrolyte Solutions