Unit 12

MixturesCombination of 2 or more different substances

Heterogeneous mixtures – can see the parts (trail mix)

Homogeneous mixtures – mixture appears uniform (Kool-aid)

Types of Mixtures1. Suspensions2. Solutions3. Colloids

SuspensionHeterogeneous mixtureParticles remain mixed with liquid when stirred but separate spontaneously over time

Example – flour & water

Flour & water

SolutionHomogeneous mixture with even distribution of particles

Can be gas (air) or solid (brass)Most often liquid

Solutes dissolved in solventAqueous solution – water is solvent

ColloidStable heterogeneous mixture

Appears homogeneous to naked eye b/c even distribution

BUT components visible under microscope

Does not settle when left to stand

Separating MixturesDecanting – pour off liquid

Separating MixturesCentrifuge – spin to separate by density

Separating MixturesFiltration – liquid through filter

Separating MixturesEvaporation – leaves behind solid

Separating MixturesChromatography - based on dissolving rates

Separating MixturesDistillation – separate by boiling point

ConcentrationRatio of solute to solventConsistent throughout solutionCalculating concentration

Parts per million (ppm)

Molality (m)

Molarity (M)

g solute1 000 000 g solvent

moles solutekg solvent

moles soluteL solution

Molarity (M)M is read as “molar” or “moles per liter”

Any amount with the same molarity will have the same concentration or ratio of solutes to solvent

So 1 mL of 1 M HCl has the same concentration as 20 L of 1 M HCl

Preparing a SolutionWhen preparing a solution, you must have the correct total volume

1.00 mole solute + 1.00 L solvent DOES NOT equal 1.00 M solution!

Instead you need 1.00 L total solution

So dissolve solute in small amount of solvent and then add more solvent to get the correct total volume of solution

Calculating Molarity0.30 moles of KBr are dissolved in 0.40 L of solution. What is the molarity?

M = 0.30 moles KBr =0.40 L solution

0.75 M KBr

Calculating MolarityWhat is the molarity of a KCl solution that has a volume of 400.0 mL and contains 85.0 g of KCl?

Two problemsGramsmL

Molarity CalculationsHow many grams of CaCl2 are needed to make 625 mL of a 2.0 M solution?

DilutionAdding solvent to solutions to decrease the concentration

Does not change the number of moles of the solute that are present

M1V1 = M2V2

Practice2.0 L of a 0.88 M solution are diluted to 3.8 L. What is the new molarity?

PracticeYou have 150 mL of 6.0 M HCl. What volume of 1.3 M HCl can you make?

SolubilityThe ability of a solute to dissolve in a solvent

Measured in terms of the amount of a solute that will dissolve in a given amount of solvent

Solubility – “Like dissolves like”Polar substances tend to dissolve in other polar substances

Nonpolar substances tend to dissolve in other nonpolar substances

Degree of polarity also mattersMiscible – liquids that are completely soluble in each other

Solubility – “Like dissolves like”Polar + nonpolar doesn’t usually dissolve

Immiscible – 2 or more liquids that do not mix with each other

How can we speed the dissolving process?Shaking or stirring

Increases the surface area contact between the solute & solvent

Increasing the temperatureMore energy available for dissolving

Effects of temp on solubilityID trends

Least solubleMost soluble

Extrapolate data200 g at 50 oC

Precipitate formed from cooling

SaturationThere is a maximum amount of solute that can be dissolvedSaturated solution

Less than that maximum amountUnsaturated solution

More than that maximum amountSupersaturated solution

Colligative PropertiesAny physical effect of the solute on the solvent

Not specific to the solute present but rather caused by the presence of a solute

ExamplesBoiling point elevationFreezing point depression