Solubility and Why Things Dissolve

Solutions

•A homogeneous mixturesolute - dissolves (usually smaller amount)

solvent – causes solute to dissolve(usually larger amount)

Types of solutes

•Electrolytes▫ Ionic compounds are hydrated▫Electrolytes conduct electricity in aqueous solutions

•Nonelectrolytes▫Molecular solutions▫Non-conductive

Types of Solutions•Solid solution (solid solvent)•Gaseous solution (gas solvent)•Liquid solution (liquid solvent)

Aqueous Solution (water solvent)

Solubility – does it dissolve?•Soluble

▫Strong electrolyte▫Strong Acids and Bases

• Insoluble (misleading)▫Always some solubility

Is lead soluble in water Why don’t we use lead pipes

▫Weak electrolyte▫Weak acids and bases

How much dissolves?SaturationUnsaturated

Less than the maximum amount of solute dissolved

Saturated Maximum amount of solute

dissolved(extra precipitates out)

SupersaturatedMore than the maximum

amount of solute dissolved

Solubility Curve

•Measure how much solute will dissolve in 100. g of water (solvent) at a particular temperature

g solute vs temperature100. H2O

Solubility Curve - Solids

The solubility of solids increases with temperature

Saturatedonline Unsaturated

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SupersaturatedOverline

Solubility Curve- Gases

The solubility of gases decreases with temperature

Water’s Unique Properties

•Universal solvent•Solid less dense than liquid•High boiling point•High surface tension

Why does water have these properties?

•Water is a polar Water is a polar moleculemolecule

•Water can form a Water can form a Hydrogen BondHydrogen Bond

Polar Molecule

•A molecule A molecule with a + with a +

and a – endand a – end

H is +H is + O is –O is –

Hydrogen bond

•+ H atoms of + H atoms of one molecule one molecule are attracted are attracted toto

•- O atoms of - O atoms of another another moleculemolecule

Why does it dissolve? “Like dissolves like”

•Polar dissolves polar▫Different ends

•Non-polar dissolves non-polar▫Same endsWill this dissolve? CO2 in H2O KBr in H2O

CO2 in CH4 KBr in CH4

Solvation

•Dissociation – decomposition of a ionic compound into hydrated ions

•Hydrated – charged ions surrounded by water molecules

•Solvation – processing of dissolving

Dissolving Salt Crystal

Lab: Solubility

Solution concentrationThe amount of solute dissolved in a specific

amount of solution

1. Written as a % (for large amounts)

g solute x 100%g solution

2. Molarity (M) Moles solute L solution

3.Molality (m) moles soluteKg solvent

Colligative Properties

•Properties that depend on the amount of solute added to solution

•Boiling point elevation•Freezing point depression

Freezing point depression

T = Kf x m x iChange in temperatureKf = freezing point constant

Molalityi= number of particles in solution

Problems

•Calculate the percent of a solution that is made of 14.6 g NaCl in 123 g water.

• If a solution is 67.3 % KI, how many g of KI are added to 376 g solution?

Problems

•Calculate the molarity of a solution with 30.0 g NaCl with water added to make 250 mL solution

•Calculate the molarity of a solution with 45.7 g KCl to make 500 mL solution

More

•Calculate the g to make 600. mL of a .35 M NaCl.

•Calculate the g to make 550 mL of a .36 M KOH

Making solutionsShow calculations to make 100 mL of .10 M using NaOH

Then go back and make it and label the flask for future use

Dilution

If you have a solution and want it at a lower Molarity

M1 x V1 = M2 x V2

Problems

•How would you dilute a 2.5 M stock solution of H2SO4 to make 200 mL of .15 M H2SO4?

Making your dilution

•Show calculation for maing 100 mL of .1 M HCl from a 2.5 M stock solution

•Then go back and make it and label the flask for future use.

Molarity•Moles per liter•M = mol / liter•Liters x Molarity = moles

L x mol = mol L

•Moles / Molarity = litersMol x 1 = L mol / L

Calculate molarity, molality

MolarityMoles per liter

Moles SoluteLiters of solution

Molality

Mole per kilogram

Moles soluteKilograms solvent

Sol

ubil

ity

(g s

olut

e/10

0g H

2O)

Sol

ubil

ity

(g s

olut

e/10

0g H

2O)

Notice at 90 C there is more solute than solvent!

This solid has a lower solubilityIn hot water than cold

There is almost no differenceIn cold and hot solubility

Temperature ºC

GasesS

olub

ilit

y (g

sol

ute/

100g

H2O

)

Warmer temperature meansLess DO (dissolved oxygen)

Poor fishies

So

lub

ility

(g

solu

te/1

00g

H2O

)

How much KNO3 will dissolve in 100.0 g of water at 80.0 C?

How much KNO3 will precipitate when a saturated solution at 80.0 C is cooled to 20.0C?

How much sugar will dissolve in 50.0 g of water at 60.0 C?

Sol

ubil

ity

(g s

olut

e/10

0g H

2O)

How much sugar will precipitate if 760 g of a saturated solution at 60 C is cooled to 20 C.

140. g

160. g