Chapter 07

Solutions and Solutions and ColloidsColloids

Solution or Colloid

• Group these?– Marshmallows– Wine– Air– Clouds– Smoke– Automobile oil– Milk of magnesia

Colloids and Solutions

• What is the difference in appearance? (Can be observed)

Characteristics of Solutions– Appearance

– Distribution of Particles

– Separation of Components

– Variable Compositions Can Be Made

Colloids

• particle diameter is between 1nm and 1000 nm• Colloid particles have very large surface areas,

which accounts for these two characteristics of colloidal systems– they scatter light and, therefore, appear turbid,

cloudy, or milky– they form stable dispersions; that is, they do not settle

out

– Solvent:Solvent:

– Solute:Solute:

Types of Solutions

SoluteSolventAppearance of Solution Example

GasLiquid Liquid Carbonated waterLiquidLiquid Liquid WineSolidLiquid Liquid Salt water (saline solution)GasGas Gas AirSolidSolid Solid 14 Carat gold

Types of Colloids

Type of Colloid Example

Gas in gasGas in liquidGas in solidLiquid in gasLiquid in liquidLiquid in solidSolid in gasSolid in liquidSolid in solid

NoneWhipped creamMarshmallowsClouds, fogMilk, mayonnaiseCheese, butterSmokeJellyDried paint

Colloids

• Tyndall effect:Tyndall effect: a characteristic of colloids in which light passing through the colloid scatters– examples of colloids that exhibit the Tyndall

effect are smoke, serum, and fog

Properties of MixturesProperty Solutions Colloids Suspensions

Partricle size (nm)Filterable with ordinary paper

Homogeneous

Settles on standing

Behavior to light

0.1 - 1.0 1 - 1000 >1000No No Yes

Yes Borderline No

No No Yes

Transparent Tyndalleffect

Translucentor opaque

Colloids and Solutions

• What is the cause of the differences? (What do we think is going on?)

• Video Link Changing a colloidal suspension into a solution with acid.

Definitions

• Solubility:Solubility:

– those compounds with low solubility are said to be insolubleinsoluble,

– those compounds with higher solubility are said to be solublesoluble

More Definitions

– saturated solution:saturated solution:

– unsaturated solution:unsaturated solution:

– supersaturated solution:supersaturated solution:

– Link to Video

Soluble or Insoluble

• Explain why some substances are soluble and other substances are not soluble by giving one example of each. Used balanced equations in you discussion.

• You may use the solubility rules page 161

Solvation

• What happens when substances dissolve? What forces are involved? Use water as a solvent for specific examples.

• Ionic?

• Covalent?

Water as a Solvent• How water dissolves ionic compounds

– water is a

– ions –

Water as a Solvent

• How water dissolves molecular compounds– nonpolar covalent molecules

– polar covalent molecules dissolve because

– Each individual molecule is

Electrolytes

Video Link-electrolytes and non-electrolytes

Video Link – Weak and strong electrolytes

Electrolytes– cations migrate to the negative electrode (the

cathode)– anions migrate to the positive electrode (the anode)– the movement of ions constitutes an electric current– electrolyte:electrolyte:

– nonelectrolytenonelectrolyte

– strong electrolyte:strong electrolyte:

– weak electrolyte:weak electrolyte:

Stoichiometry

• How can we count particles in a solution?

Percent Composition

• Percent composition:– weight of solute per volume of solution (w/v)weight of solute per volume of solution (w/v);

• a solution of 10 g of table sugar in 100 mL of solution, for example, has a concentration of 10 percent w/v

– weight of solute per weight of solution (w/w);weight of solute per weight of solution (w/w); • essentially the same as w/v except that the weight

of the solution is used instead of its volume

– volume of solute per volume of solution (v/v);volume of solute per volume of solution (v/v); • example, a solution of 40 mL of ethanol in 100 mL

of aqueous solution is 40 percent v/v

Molarity• Molarity:Molarity: moles of solute per liter of solution

– example:example: tell how to prepare 2.0 L of 0.15 M NaOH– first we find the number of moles of NaOH required

– next convert 0.30 mol NaOH to g NaOH

Molarity (M) = moles of solute (n)liter of solution (L)

4.5

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

What mass of KI is required to make 500. mL ofa 2.80 M KI solution?

volume KI moles KI grams KIM KI M KI

4.5

Molarity

– problem:problem: the concentration of NaCl in blood serum is approximately 0.14 M. What volume of serum contains 2.0 g of NaCl?

– first find the number of moles NaCl in 2.0 g NaCl

– next find the volume in liters that contains this many moles of NaCl

Molarity

• If we dilute a solution, the number of moles of solute remains the same; use this relationship:

M1V1 = M2V2

– problem:problem: how do you prepare 200 mL of 3.5 M aqueous solution of acetic acid if you have a bottle of 6.0 M acetic acid

– first find the number of L of 6.0 M acetic acid needed

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=4.5

How would you prepare 60.0 mL of 0.200 MHNO3 from a stock solution of 4.00 M HNO3?

MiVi = MfVf

4.5

Colligative Properties

• Colligative property:Colligative property: any property of a solution that depends on the number of solute particles, and not on the nature of the particles

• We study two colligative properties– freezing-point depression– osmosis

Freezing-Point Depression• One mole of any particle dissolved in 1000 grams of

water lowers the freezing point of water by 1.86°C– the nature of the particles does not matter, only the

number of particles

• Depression of freezing point has a number of practical applications– we use NaCl and CaCl2 to melt snow and ice

– we use ethylene glycol as antifreeze in automobile radiators

T = mol x mol of particles1.86°C

Freezing-Point Depression– Problem:Problem: if we add 275 g of ethylene glycol, C2H6O2, per

1000 g of water in a car radiator, what will be the freezing point of the solution?

– ethylene glycol is a molecular compound; it dissolves in water without dissociation

– first find the number of moles of ethylene glycol

– each mole lowers the freezing point by 1.86°C

– the freezing point of the solution will be

Freezing-Point Depression

– Problem:Problem: what will be the freezing point of a solution prepared by dissolving one mole of K2SO4 in 1000 grams of water?

– K2SO4 is an ionic solid and dissociates to ions when dissolved in water

– one mole of K2SO4 gives three moles of ions

– the freezing point is lowered by

Osmosis

Osmosis– semipermeable membrane:semipermeable membrane: a membrane with tiny pores

that are big enough to allow solvent molecules to pass through them, but not big enough to allow the passage of large solute molecules

– osmosis:osmosis: the movement of solvent particles through a semipermeable membrane from a region of lower solute concentration (higher solvent concentration) to a region of higher solute concentration (lower solvent concentration)

– osmotic pressure:osmotic pressure: the pressure necessary to prevent osmosis

– osmolarity (osmol):osmolarity (osmol): the molarity multiplied by the number of particles produced by each formula unit of solute

Osmosis– Isotonic solutions:Isotonic solutions: solutions with the same osmolarity– isotonic solution:isotonic solution: a term used primarily in the health

sciences to refer to a solution with the same osmolarity as blood plasma and red blood cells

– hypotonic solution:hypotonic solution: a solution with lower osmolarity than blood plasma and red blood cells

– hemolysis:hemolysis: the swelling and bursting of red blood cells because they cannot resist the increase in osmotic pressure when put into a hypotonic solution

– hypertonic solution:hypertonic solution: a solution with higher osmolarity than red blood cells

Osmosis– Problem:Problem: an 0.89 percent w/v NaCl solution is

referred to as physiological saline solution. What is the osmolarity (osmol) of this solution?

– 0.89 w/v NaCl = 8.9 g in 1 L of solution– first we calculate the number of moles of NaCl in this

solution

– because each mole of NaCl dissolved in water dissociates into two ions, the osmolarity of the solution is