Solutions are one of the most important topics in all of chemistry. Most chemical reactions take place in aqueous solutions, including biochemical reactions in our blood. Because the amount of stuff dissolved

in a liquid has a huge effect on how that liquid behaves, we need to know how to define

concentration.

A homogeneous mixture of one or more substances dissolved in another substance.

Examples of SolutionsExamples of Solutions

Alloys – Alloys –

Air – a solution of gasesAir – a solution of gases

Aqueous solutions – things dissolved in waterAqueous solutions – things dissolved in water Ex) salt water, Kool-AidEx) salt water, Kool-Aid

solutions of metalssolutions of metalsEx) Brass = zinc + Ex) Brass = zinc + coppercopper

Properties of Liquid SolutionsProperties of Liquid Solutions

Solutions are homogeneous mixturesSolutions are homogeneous mixtures

Solutions are transparent and do not Solutions are transparent and do not

disperse lightdisperse light

Solutions can have colorSolutions can have color

Solutions will not settle on standingSolutions will not settle on standing

Solutions will pass through a filterSolutions will pass through a filter

Solution Colloid

Parts of a SolutionParts of a Solution

Solute = The substance being dissolved – present in the smaller amount

Solvent = The substance that dissolves the solute – present in the larger amount

Label the Parts:Label the Parts:

Solution Solvent Solute

Chocolate Milk:Choc. Syrup + Milk

Kool-Aid:Water + Drink Powder

Seltzer:CO2 + Water

Milk Choc. Syrup

Water Drink Powder

Water CO2

ConcentrationsConcentrations

Unsaturated -Unsaturated -

Saturated -Saturated -

Can still dissolve more solute.

If you place sugar in your iced tea you’ve made an unsaturated solution, because if you were to add more sugar, it would also dissolve.

Has dissolved as much solute as it possibly can.

If you added sugar to your iced tea until it was saturated, any sugar you add after that point sinks to the bottom, never dissolving.

Concentrations Cont.Concentrations Cont.

Supersaturated -Supersaturated - Holds more solute than a saturated solution at the same temperature - Very unstable.

If you added sugar to your iced tea when it was supersaturated, all of the dissolved sugar would suddenly crystallize out.

Solubility FactorsSolubility Factors

Can anything dissolve? Can anything dissolve?

What factors can affect solubility?What factors can affect solubility?

TemperatureTemperature: As T : As T ↑ most solids become more ↑ most solids become more

soluble in water, but gases become less solublesoluble in water, but gases become less soluble

PressurePressure: Doesn’t affect solids or liquids, but : Doesn’t affect solids or liquids, but

gases become more soluble in liquids as P gases become more soluble in liquids as P ↑↑

Nature of Solute and Solvent: Nature of Solute and Solvent:

Nature of Solute and SolventNature of Solute and Solvent

How does a solute dissolve?How does a solute dissolve?

In a solution, why do substances dissolve in one In a solution, why do substances dissolve in one another?another? Some of the attractive forces between the

particles of each component must be overcome

The particles of all of the components must be able to attract each other with forces of similar strength.

““Like Dissolves Like”Like Dissolves Like”

If the solvent and solute are of the If the solvent and solute are of the same polarity, dissolution will occursame polarity, dissolution will occur

Let’s review polarity . . .

Remember – polar molecules have Remember – polar molecules have positive and negative ends: dipolespositive and negative ends: dipoles

Polarity ReviewPolarity Review

Polarity of bonds vs. polarity of moleculesPolarity of bonds vs. polarity of molecules Polar bonds have an electronegativity Polar bonds have an electronegativity

difference of greater than difference of greater than

Polar molecules are Polar molecules are asymmetricalasymmetrical. .

Must contain at least 1 polar bondMust contain at least 1 polar bond

Bond polarities Bond polarities do notdo not cancel each other cancel each other

outout

““Tug of War”Tug of War”

0.4

Polarity PracticePolarity Practice

Formula Lewis Diagram Polar?

CO2

CH3Cl

H2O

(Remember that molecules have 3-D shapes!)

CO O

OOHHHH

CCHHHHHHClCl

No

Yes

Yes

Polar Solutes & SolventsPolar Solutes & Solvents

Salt Water

Cl

Na

When a positive charge from a polar solvent lines up with a negative charge from a polar solute, they attract one another and the solute is pulled into solution.

Dipole-Dipole Interactions

Polar SolutesPolar Solutes

A nonpolar solvent can’t get in between the polar solute ions

A polar solvent can get in between the polar solute ions

Nonpolar SolutesNonpolar SolutesPolar solvent molecules don’t grab on to nonpolar solutes because they’d rather be grabbing other polar solvent molecules.

Nonpolar solvents dissolve nonpolar solutes because attractions between the molecules in both the solvent and the solute aren’t very strong.

Soluble or Not?Soluble or Not?Label each substance as polar or nonpolar, then decide whether Label each substance as polar or nonpolar, then decide whether

the solute would dissolve or not for each given set of solutes the solute would dissolve or not for each given set of solutes and solvents:and solvents:

Solvent Solute Solution?

CH4

HCl

LiBr

CCl4 I2

KCl

Nonpolar

Nonpolar

Polar

Nonpolar

Polar

Polar

Yes

No

Yes