chapter 2 an an introduction to introduction to...

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Chapter 2Chapter 2

An An Introduction to Introduction to ChemistryChemistry

Lecture 8: SolutionsLecture 8: Solutions

•• A solution is a homogenous mixture of one or A solution is a homogenous mixture of one or

more solutes dissolved into a solventmore solutes dissolved into a solvent

•• Solute:Solute: what is dissolvedwhat is dissolved

•• Solvent:Solvent: what is doing the dissolvingwhat is doing the dissolving

•• Aqueous solution: Aqueous solution: one in which the solvent is one in which the solvent is

waterwater

SolutionsSolutions

•• Concentration: Concentration: a measure of how much solute is a measure of how much solute is

dissolved into a given amount of solventdissolved into a given amount of solvent

•• Concentrated: Concentrated: high proportion of solute to solventhigh proportion of solute to solvent

•• Dilute:Dilute: low proportion of solute to solventlow proportion of solute to solvent

•• Terms are mostly useful for comparing solutions with Terms are mostly useful for comparing solutions with

like componentslike components

ConcentrationConcentration

•• Usually more useful to have a quantitative Usually more useful to have a quantitative

measure of concentrationmeasure of concentration

•• Noted as [X] (Example: [HNoted as [X] (Example: [H++])])

•• Many ways to measure concentrationMany ways to measure concentration

•• Several based on the moleSeveral based on the mole


•• Based on Avogadro’s number = 6.022 x 10Based on Avogadro’s number = 6.022 x 102323

•• A mole of something contains 6.022 x 10A mole of something contains 6.022 x 1023 23

pieces of itpieces of it

•• Marshmallows, nails, doughnuts, atoms, ions,Marshmallows, nails, doughnuts, atoms, ions,

molecules molecules –– anything!!anything!!

•• A real number, but hard to conceptualize A real number, but hard to conceptualize

because it’s so bigbecause it’s so big


•• MolarityMolarity:: Concentration Concentration

measured in moles of measured in moles of

solute per liter of solute per liter of

solutionsolution

•• Written as MWritten as M

M = M = mol solutemol solute

Liters solutionLiters solution

•• Note that this is Note that this is NOTNOTliters of solvent!!!liters of solvent!!!

•• Water displacementWater displacement


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•• Question: which contains more solute?Question: which contains more solute?

•• 1L of 0.5M 1L of 0.5M NaClNaCl



•• Question: So which is more concentrated?Question: So which is more concentrated?




•• MolalityMolality:: Concentration measured in moles of Concentration measured in moles of

solute per kilogram of solventsolute per kilogram of solvent

•• Essentially the only time we consider solvent Essentially the only time we consider solvent

instead of solutioninstead of solution

•• Written as mWritten as m

•• At room temperature 1L HAt room temperature 1L H22O = 1 kgO = 1 kg

•• For aqueous solutions, if you do not For aqueous solutions, if you do not

take water displacement into accounttake water displacement into account

when calculating when calculating molaritymolarity, you , you

accidentally calculate accidentally calculate molalitymolality instead!instead!


•• Percent solution (w/w): Percent solution (w/w): Concentration measured Concentration measured in mass solute per mass of SOLUTION (change in mass solute per mass of SOLUTION (change in study guide)in study guide)

% solution = % solution = mass solute (g)mass solute (g) x 100x 100

mass solution (g)mass solution (g)

•• Also can have percentage volume by volume (v/v) Also can have percentage volume by volume (v/v) or percentage weight by volume (w/v)or percentage weight by volume (w/v)

•• In all cases, consider the amount of solution, In all cases, consider the amount of solution, NOT solventNOT solvent


•• Compare the following solutionsCompare the following solutions

•• 1L 10% glucose1L 10% glucose

•• 1L 20% glucose1L 20% glucose

•• Which solution is more concentrated?Which solution is more concentrated?

•• Which solution has more solute?Which solution has more solute?

•• Which solution has more solvent?Which solution has more solvent?

ConceptsConcepts

•• The molar mass of MgClThe molar mass of MgCl22 is 95g/mol. How many is 95g/mol. How many

grams of MgClgrams of MgCl22 must be used to make 0.5L of a must be used to make 0.5L of a

0.1M solution?0.1M solution?

ConceptsConcepts

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•• Suspension: Suspension: a heterogeneous aqueous mixturea heterogeneous aqueous mixture

•• Particles remain largeParticles remain large

•• Will eventually settle into layersWill eventually settle into layers

•• NOT a solutionNOT a solution

•• Examples: sand and water, oil and waterExamples: sand and water, oil and water

Aqueous MixturesAqueous Mixtures

•• Colloidal dispersion: Colloidal dispersion: a homogeneous aqueous a homogeneous aqueous

mixture with large particles that does not settlemixture with large particles that does not settle

•• Examples: gelatin, homogenized milkExamples: gelatin, homogenized milk

Aqueous MixturesAqueous Mixtures

•• Homogenous mixturesHomogenous mixtures

•• Small particle size of soluteSmall particle size of solute

•• Solute particles separate from each other andSolute particles separate from each other and

become surrounded by water moleculesbecome surrounded by water molecules

•• Form Form hydration sphereshydration spheres

Aqueous SolutionsAqueous Solutions

•• Two options for dissolved solutes…Two options for dissolved solutes…

1.1. Crystal structure breaks down but molecules Crystal structure breaks down but molecules

remain intactremain intact

Aqueous SolutionsAqueous Solutions

•• Two options for dissolved solutes…Two options for dissolved solutes…

2. Solute completely breaks down and ions 2. Solute completely breaks down and ions

dissociate from each otherdissociate from each other

•• These dissociated ions will conduct These dissociated ions will conduct

electricity electricity –– called called electrolyteselectrolytes

Aqueous SolutionsAqueous Solutions Best Example: BloodBest Example: Blood

Cells = suspensionCells = suspension Proteins = colloidal dispersionProteins = colloidal dispersion

Glucose = dissolved but intactGlucose = dissolved but intact Ions = dissolved and dissociatedIons = dissolved and dissociated

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•• Not all solutes will dissolve in all solventsNot all solutes will dissolve in all solvents

•• Solubility rule of thumb: Solubility rule of thumb: Like dissolves likeLike dissolves like

•• Polar Polar and ionicand ionic solutes dissolve in polar solventssolutes dissolve in polar solvents

•• NonNon--polar solutes dissolve in nonpolar solutes dissolve in non--polar solventspolar solvents

Solvents and SolutesSolvents and Solutes Solvents and SolutesSolvents and Solutes

Sugar (polar) +Sugar (polar) +Water (polar)Water (polar)

Sugar (polar) +Sugar (polar) +CClCCl44 (non(non--polar)polar)

Iodine (nonIodine (non--polar) +polar) +Water (polar)Water (polar)

Iodine (nonIodine (non--polar) +polar) +CClCCl44 (non(non--polar)polar)

Like dissolves likeLike dissolves like

•• Substances that associate with water = Substances that associate with water =

hydrophilichydrophilic (water(water--loving) loving) –– Polar or nonPolar or non--polar?polar?

•• Substances that do not associate with water = Substances that do not associate with water =

hydrophobichydrophobic (water(water--fearing) fearing) –– Polar or nonPolar or non--polar?polar?

•• Some molecules are bothSome molecules are both

Solvents and SolutesSolvents and Solutes

•• Define the following as…Define the following as…

•• Mixtures or solutionsMixtures or solutions

•• If a mixture: suspension or colloidal dispersionIf a mixture: suspension or colloidal dispersion

•• If a solution: particles intact or dissociatedIf a solution: particles intact or dissociated

•• All mixed with waterAll mixed with water

ActivityActivity

Oil Gelatin and fruit

chapter 2 an an introduction to introduction to...

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