Solutions and Solubility

A solution is composed of:Solute: the substance being dissolved

Usually a solid. Can be a gas or another liquid.

Solvent: the substance doing the dissolvingUsually water (aq)

Soluble: when a solid is able to dissolve in a liquid

Insoluble: when a solid cannot dissolve (precipitate)

Immiscible: two liquids that will not mix

Miscible: two liquids that will mix

Solvation process:What is happening at the molecular level when a

solid dissolves in a liquid?

The solid must be “picked apart” layer by layer by the liquid.

Water makes a great solvent because it is polar.

The polar water molecule

Dissolving of NaCl

Timberlake, Chemistry 7th Edition, page 287

Suga

Sugar molecules will remain covalently bonded, but still be

dispersed within the water.

The water molecules will attract and dissolve ions layer by layer

What factors affect the rate of solution formation?

1. TemperatureHot: water molecules move rapidly and contact

solid often.

Cold: water molecules move slowly. Little contact.

2. Concentration of solute or solvent

More solvent: increases rate of liquid coming into contact with solid.

More solute: Less water to suspend solid.

3. StirringMechanically forces solute and solvent together

for solvation to occur.

4. Surface area of substance

The larger the surface area (larger crystal), the more layers there are to pick apart.

Smaller crystals also have more surface area in proportion to their volume.

5. PressureApplying pressure forces the molecules to

interact.

6. Type of substancesSome solutes are

more easily dissolved due to less “intermolecular” attraction.

Some liquids are better solvents (polarity).

Essential question: What factor has the greatest effect on the

rate of solution formation?

Choose any two factors.

You must test an increase and a decrease for each factor.

You must have a control.

You should keep all other conditions constant.

How do we measure the concentration of a

solution?

1. Percent Concentration:

Used more in “every day” life.

What are some examples of solutions in your world?

% Concentration = Mass or volume of solute X

100

Mass or volume of solute + solvent

Remember: solution = solute + solvent

Examples for % concentration:

1. What is the concentration of a solution that has 25 grams of salt dissolved in 250 ml of water?

2. Ocean water has a salt concentration of 3.5% How much salt and water would I need to make 500 ml of ocean water?

3. Power equipment uses a 2% oil/gas mixture. How much oil (solute) and gas (solvent) would I need to make 2 liters?

2. Molarity and Molar concentrations

How chemists make solutions.

A 1 molar solution is a solution in which 1 mole of a compound is dissolved in a total volume of 1 litre.

1 M = molar mass of solute dissolved in

total volume of 1000 ml

How to make a molar solution:1. Determine chemical

formula of solute.

2. Calculate molar mass of solute.

3. Dissolve solute in water to a final volume of 1000 ml.

Molarity examples:1. How do you make a one molar solution of calcium

chloride?

2. How do you make 500 ml of a one molar solution of calcium chloride?

3. How do you make a 2 molar solution of sodium chloride?

4. What is the molarity of a sodium chloride solution that has 30 grams dissolved in 1000 ml?

Lab:What percent concentration of Kool-Aid will bring the greatest concentration?

Solubility:How much of a solid will dissolve in

a given amount of liquid at a given temperature.

Often look at solubility curves, or saturation curves.

Solubility of a Solid

Solubility of a Gas

To

Sol.

To

Sol.

Solids dissolved in liquids Gases dissolved in liquids

As Temperature increases, Solid solubility increases.

As Temperature increases, Gas solubility decreases.

What type of solutions exist?

SATURATED SOLUTION

no more solute can be

dissolved

UNSATURATED SOLUTION

more solute can be dissolved

SUPERSATURATED SOLUTION

Contains more solute than it

normally would at that temperature.

increasing concentration

A supersaturated solution is unstable, and crystallization will occur upon cooling.

A “seed” crystal will disturb the equilibrium and start the crystallization process.

Let’s watch…

http://www.stevespanglerscience.com/experiment/00000078

Solubility of Sodium Acetate

Temperature (oC)

025 50 75 100

Solu

bili

ty(g

/100 g

H2O

)

50

100

150Supersaturated

solution

Unsaturated solution

Saturated

Charles H.Corwin, Introductory Chemistry 2005, page 378

In the world of solubility, “Like dissolves Like”

Polar solvents will dissolve polar molecules.

Non-polar solvents will dissolve non-polar molecules.

Example: Oil-based paint is non-polar, and requires non-

polar paint remover for cleaning.Water-based paint can be cleaned with water.

Can you think of any other examples?

Vitamins

Multi Vitamin Provides many essential

vitamins “Expensive urine”

Water Soluble Vitamin C Must be replenished

regularly

Fat Soluble Can overdose Vitamin A Can be ingested periodically,

stored in body fat