II

III

I

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The Nature of Solutions

SolutionsSolutions

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MixturesMixtures

Can be divided into two categories:• Heterogeneous (different throughout)

–Suspensions

–Colloids• Homogeneous (same throughout)

–Solutions

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MixturesMixtures

Can also be classified according to the size of their solute.• Solution < 1nm• Colloid 1-1000 nm• Suspension >1000nm

FYI: 1nm = 1 x 10-9 m = 0.000000001m (in other words…really small!)

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Types of MixturesTypes of Mixtures

Solutions, Colloids, and Suspensions (based on size of solute)

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SuspensionsSuspensions

Particles in a suspension settle out.Examples: oil and water, paint, mud in

water, flour in water

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ColloidsColloids

Particles in a colloid scatter light, but are usually not visible to the human eye.

Examples: Milk, fog, mayonaise, shaving cream, jelly, blood

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SolutionSolution

Particles in a solution are never visible, and do not scatter light.

Example: sugar and water

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Tyndall EffectTyndall Effect

Scattering of light by colloidal particles• Used to distinguish a colloid from a

solution

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DefinitionsDefinitions

Solution - Solution - homogeneous mixture made by dissolving one substance (solute) into another substance (solvent).

Solvent Solvent – substance that dissolves the solute

Solute Solute - substance being dissolved

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SolutionsSolutions

The solute dissolves in the solvent!

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SolutionsSolutions

Solute + Solvent =Solute + Solvent = SolutionSolution

This makes a solution!

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SolubilitySolubility

Solubility is the measure of how “dissolvable” a substance is.

(maximum grams of solute that will dissolve in

100 g of solvent at a given temperature) Some substance will not dissolve

insoluble Some will dissolve

Soluble

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Factors that Affect SolubilityFactors that Affect Solubility

Temperature

• solids, liquids increased temperature leads to an increase in solubility

• gases increase in temperature leads to a decrease in solubility

What does this mean?

• Solids dissolve better at higher temperatures while gases dissolve better at lower temperatures!

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Solubility CurveSolubility Curve

shows the dependence of solubility on temperature

As temperature increases, the solubility of most solids increases and the solubility of gases decreases.

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Factors that Affect SolubilityFactors that Affect Solubility

Pressure• Affects the solubility of gases in liquids

*Gases dissolve better at higher pressures!

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Factors that Affect SolubilityFactors that Affect Solubility

Nature of the Solute

• Water is called the universal solvent because it is a polar molecule (making it easy to dissolve most things).

• Polar solutes dissolve in polar solvents.

• Non-polar solutes dissolve in non-polar solvents.

• “Like dissolves Like”

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Factors that Affect SolubilityFactors that Affect Solubility

NONPOLAR

NONPOLAR

POLAR

POLAR

““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”

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Types of SolutionsTypes of Solutions

When you dissolve one substance into another, a limited amount of solute can be dissolved in a given amount of solvent.

Three types of Solutions can be made:• Unsaturated• Saturated• Supersaturated

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Types of SolutionsTypes of Solutions

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

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Solubility CurveSolubility Curve

Where they are on a solubility curve

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Factors affecting the RATE of dissolving

Factors affecting the RATE of dissolving

Temperature Heat it!Surface Area Crush it!Agitation Stir it!

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ElectrolytesElectrolytes

StrongElectrolyte

Non-Electrolyte

All of it Ionizes

Bright Light

- +

salt

- +

sugar

None of it ionizes

No Light

- +

acetic acid

WeakElectrolyte

Some of it ionizes

Weak Light

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Units of Concentration:Units of Concentration:

1. Percent by Mass

% = mass of solute x 100

mass of solute + solvent

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Example:Example:

A solution of NaCl is prepared

by dissolving 5.0g of salt in

550.5g of water. What is the

percent by mass concentration

of this solution?

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Example:Example:

A solution of sugar water is

prepared by dissolving 124.8

grams of glucose in 1775 grams

of water. What is the percent by

mass concentration of this

solution?

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Units of Concentration:Units of Concentration:

2. Molarity

M = moles solute

Liters of solution

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Example -Example -

What is the molarity of a

solution composed of

5.85g KI dissolved in

0.125L of solution?

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ExampleExample

How many moles of solute are

present in 10.2 liters of a 3.5

Molar solution?

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Units of Concentration:Units of Concentration:

3. Molality

m = moles solute

kg of solvent

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Example -Example -

What is the molality of a solution composed of 2.55g of acetone (CH3)2CO, dissolved in 200.0g water?

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Example:Example:

If a 6.0 molal solution contains 7.19 moles of solute, what is the mass, in kg, of solvent?