Solutions

CPS Chemistry

Definitions

Solutions A homogeneous mixture of two or more

substances in a single phase Soluble

Capable of being dissolved

Solvent Dissolving medium in a solution

What is doing the dissolving

Solute Substance dissolved in a solution

What is dissolved

Example Sugar in tea –

tea is solvent, sugar solute

Types of Solutions

May exist as gasses, liquids or solids One component is designated as

solvent and one as solute Chart on pg. 396

Phase If there are two different types of

substances it is a phase change Water + salt; water and gas

Same phase Water and apple juice

This is an aqueous solution Means there is water involved

Alcohol and liquid Tincture solution Means there is alcohol involved

Mixtures

2 or more substances when each retains its properties

Homogeneous Uniform distribution of particles 0.01-1nm size particles, can be atoms Can be physically separated Ex. Salt water, air Also called solution

Heterogeneous Distribution of particles is not uniform

Can be separated by physical means

Particle size 1-1000 nm (nanometer)

Suspensions

When particles in a solvent are so large that they settle out unless stirred constantly

Gravity pulls particles to bottom of container

Particles >1000nm in diameter, 1000 times as large as atoms

Ex. Italian salad dressing, muddy water

Can be separated by passing liquid through a filter

Colloids

Has particles that are intermediate in size and they remain dispersed in the solute

1-1000nm particle size Emulsion or foam are specific types Mayonnaise is an emulsion of egg and

oil

The Tyndall effect

Is a sign that it may be a colloid The particles are not large enough to

be seen, but large enough to scatter light

Ex: headlights on a foggy night

Test tube

Light Beam

Test tube

Light Beam

Tyndall Effect, beam of light can be seen in suspensions and colloids

No Tyndall Effect, beam of light cannot be seen in solutions

Electrolytes vs. Nonelectrolytes

Electrolyte A substance that dissolves in water to

give a solution the ability to conduct electricity

Nonelectrolyte A substance that when dissolved in water

to make a solution that does not conduct electricity

When ionic compounds dissolve, the positive and negative ions separate from each other and are surrounded by water molecules

When the ions are free to move, electricity moves easily

How to Make Solutions

You need to know the: Solubility –the maximum amount solute

can dissolve in a solvent Rate – how fast the solute dissolves

Factors that affect rate of dissolution

Surface area of the solute The larger the surface area, the more

quickly it dissolves Agitation of a solution

When you stir or shake the solute particles are dispersed throughout the solvent, and it increase the rate of dissolution

Saturated Solutions A solution that contains the maximum

amount of dissolved solute is saturated

The factors that determine saturation are mass of solvent, mass of solute and the temperature

When a solution contains less than the maximum saturation it is considered unsaturated

Supersaturate

A solution that contains more dissolved solute than a saturated solution contains under the same conditions

But will form crystals when disturbed or cooled

Like dissolves like

The rule for predicting whether one substance will dissolve in another is related to the type of bonding, the polarity of a molecule and the intermolecular forces between the solute and solvent

Things need to be similar for them to dissolve

Solvent Solute = Solution

Polar Polar = yesPolar non-polar= noNonpolar Polar = noNonpolar Nonpolar = yes

Reminder molecule polarity

More Vocab.

Immiscible Liquid solutes and solvents that are not

soluble in each other Oil and water Oil and salt

Miscible Liquids that dissolve freely in one

another in any proportion Water and food coloring

Back to Temperature- Solubility Increase temp =increase KE=

increase in solubility + increase in rate Higher temps dissolve faster( Liquids)

BUT Gasses act differently

Increase temp = decrease solubility Because gasses will leave solution at high

temps

Pressure –solubility

There is no difference to solids or liquids, but with an increase in pressure it will increase the solubility of a gas For example CO2 dissolved in a solution

of sucrose and water (soda) will come out of solution when the pressure is decreased (opening the bottle, lets the soda bubble)

Size of the Particle – rate

Because the dissolution occurs only at the surface of the solute, when you crush a substance,

You get a larger surface, so you increase the rate at which it is dissolved

Stirring - rate

When you agitate the solvent, you increase the contact with the surface of the solute

You increase the rate

Amount of Solute -rate

As you increase the amount of solute you want to dissolve

You decrease the solubility and rate

Concentration

A measure of the amount of solute in a given amount of solvent or soulution

MATH IS INVOLVED

Molarity The number of moles of solute in one

liter of solution Molar mass- as a reminder it is the

mass listed on the PTE.. If it is for a compound, you simly add the masses of the atoms of the emperical formula

Ex. H2O H=1.00 O=15.99 total molar mass is 1.00+1.00+15.99 =17.99g

Formula

Amount of solute (mol)

Molarity ( M) = ______________________ Volume of solution (L)

Practice

You have3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that soulution?

Mass of solute 90.0 Solution volume = 3.50 L Molar Mass if NaCl 58.44 g/mol

Molality

Don’t confuse them… The concentration of a solution

expressed in moles of solute per kilogram of solvent

You measure the mass of the solvent…

Formula

moles of solute (mol)Molality = ______________________

mass of solvent (Kg)

Practice

A solution was prepared by dissolving 17.1 g of sucrose C12H22O11 in 125g of water. Find the molal concentration

Given Solute mass = 17.1g sucrose Solvent mass = 125 g H2O

Colligative Properties

Boiling- point elevation Freezing-point depression Vapor-pressure lowering Osmotic pressure

These change in relation to the total number of solute particles present

They are a constant that can be used to calculate the changes in solvents that contain nonvolatile solutes

Electrolytes have greater affects on colligative properties