4 - 1 Aqueous Solutions. 4 - 2 Essential Questions: Why does something dissolve? Can an unlimited quantity of a substance dissolve in H 2 O? What quantities

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Aqueous Aqueous SolutionsSolutions

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Essential Questions:Essential Questions:

Why does something dissolve?

Can an unlimited quantity of a substance dissolve in H2O?

What quantities (units) are used to express solubility & concentration?

What are acids and bases?

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A homogeneous mixture of two or more components.

A homogeneous mixture of two or more components.

SolutionsSolutions

A solution is:A solution is:

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A solution consists of two component types.

solventsolvent - component doing the dissolving

solutesolute - component being dissolved(You may have more than one.)

In a solution

•The solute can’t be filtered out.•The solute always stays mixed.•Particles are always in motion.•Volumes may not be additive.•A solution will have different properties than the solvent

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Physical states of solutionsPhysical states of solutions

Solutions can be made that exist in any of the three states (or phases).

Solid solutionsSolid solutionsdental fillings, 14K gold, sterling silver

Liquid solutionsLiquid solutionssaline, vodka, vinegar, sugar water

Gas solutionsGas solutionsthe atmosphere, anesthesia gases

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The solution is always in The solution is always in the same phase as the the same phase as the solvent. solvent.

THIS IS NOT ALWAYS THE LARGER THIS IS NOT ALWAYS THE LARGER VOLUME OR MASS COMPONENT.VOLUME OR MASS COMPONENT.

If the solvent and the solution are If the solvent and the solution are the same phase, then the solvent is the same phase, then the solvent is

the larger quantity.the larger quantity.

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Solid solutions: Solid solutions: the solvent is solid like the resulting solution.the solvent is solid like the resulting solution.dental amalgams: liquid mercury in solid silver

Liquid solutions: Liquid solutions: the solvent is liquid like the resulting solution.the solvent is liquid like the resulting solution.sugar water: solid sugar in liquid waterrubbing alcohol: liquid water in liquid isopropanolsoda under pressure: CO2 gas in liquid watertinctures: solid medicines in liquid ethanol

Gas solutions: Gas solutions: the solvent is gas like the resulting solution.the solvent is gas like the resulting solution.humid air: liquid water in gas phase

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SolutionsSolutionsSolutions are always in a single phase.Solutions are always in a single phase.

Carbonated soda, once opened and you can see the gas bubbles in the liquid is NOT a solution. When the soda is sealed and the carbon dioxide is “dissolved” in the liquid (usually due to pressure), it is a solution.

Aqueous solutionsAqueous solutions

Solutions where water is the solvent.

Other common termsOther common termsalloy: solutions of two or more metals: steeltincture: ethanol is solvent; used in medicine/pharmacyamalgam: mercury is solute with another metal: dentistry

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HOMEWORK: HOMEWORK: Define following termsDefine following terms

•Heterogeneous•Homogeneous•Solution•Aqueous solution•Solute•Solvent•Tincture•Miscible•Immiscible•Alloy•Amalgam

•Electrolyte•Nonelectrolyte•Hydrated ion•Dissociation•Solubility limit•Solubility curve•Solution equilibrium•Unsaturated solution•Saturated solution•Supersaturated solution•Colligative property

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Properties of Aqueous Properties of Aqueous SolutionsSolutions

There are two general classes of solutes.

ElectrolyticElectrolytic•ionic compounds in polar solvents•dissociate in solution to make ions•conduct electricity•may be strong (100% dissociation) or

weak (less than 100%)

NonelectrolyticNonelectrolytic•do not conduct electricity•solute is dispersed but does not

dissociate

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Dissolving Ionic Compounds in Dissolving Ionic Compounds in HH22OO

When an ionic solid dissolves in water, the solvent removes individual ions from the crystal. The positive ions separate from the negative ions.

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Dissolving Ionic Compounds in HDissolving Ionic Compounds in H22OO

This process is called “DISSOCIATION”. The individual ions are “hydrated” with many water molecules.

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Dissolving Ionic Compounds in HDissolving Ionic Compounds in H22OO

http://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html

Click link for alternate movie/video

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Electrolytes in HElectrolytes in H22OO

The dissociated ions are charged particles!

These charged particles act as a conductor and can transfer electricity.

NaCl(s) Na+(aq) + Cl-(aq)

Strong electrolyte dissociate completely. The dissociate ions are free to move

around.

Many salts(ionic compounds), some acids and some bases are strong electrolytes.

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Weak Electrolytes in HWeak Electrolytes in H22OO

Weak electrolytes only dissociate slightly.

These charged particles act as a conductor and can transfer electricity, but there are not as many of them.

HC2H3O2(l) H+(aq) + C2H3O2

-(aq)

For weak electrolytes, the dissociation is reversible and in equilibrium.

Some acids and some bases are weak electrolytes.

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Dissolving covalent compoundsDissolving covalent compounds

Covalent compounds do not dissociate. Acids are an exception (see weak electrolytes)

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Dissolving Covalent Compounds in Dissolving Covalent Compounds in HH22OO

Ability of a solvent to dissolve a solute depends on attraction of polar dipole ends of water to the solute.

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Dissolving Covalent Compounds in Dissolving Covalent Compounds in HH22OO

Non polar solutes do not dissolve in polar H2O.

No attraction!

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Typical substances:Typical substances:Common POLAR substances:

•Water H2O• Ammonia NH3

• Acetone C3H6O

Alcohols, -OH, are slightly polar, bridge the two categories: POLAR and NONPOLAR

Common NON POLAR Substances:• Benzene C6H6

• Toluene C7H8

• Carbon tetrachloride CCl4•Oils, gasoline, waxes, tar, diatomic molecules

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SolubilitySolubility

Factors affecting solubility:Factors affecting solubility:

LIKES DISSOLVE LIKES!

General rule only!

Substances, like alcohols, which are only slightly polar, can dissolve nonpolar substances, like oils/waxes/etc. and polar substances, like water/sugar/etc.

However, it’s not polar enough to dissolve ionic compounds.

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A measure of how much of a solute can be dissolved in a solvent.

Factors affecting solubility:Factors affecting solubility:

POLARITY of Solute AND Solvent!

Ionic Compounds (so extremely polar, there ionic):typically dissolve in polar solvents like waterbut not in nonpolar solvents like oil.

Covalent Compounds:Nonpolar: dissolves in nonpolar solventsPolar: dissolves in polar solvents

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A measure of how much of a solute can be dissolved in a solvent.

Common unit- grams solute / 100 g of solvent

Factors affecting solubilityFactors affecting solubility•Polarity•Temperature

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Solubility of some substancesSolubility of some substances

Temperature SolubilitySubstance oC g/100 ml water

NaCl (s) 100 39.12

PbCl2 (s) 100 3.34

AgCl (s) 100 0.0021

CH3CH2OH (l) 0 - 100 infinity

CH3CH2OCH2CH3 (l) 15 8.43

O2 (g) 60 0.0023

CO2 (g) 40 0.097

SO2 (g) 40 5.41

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SaturationSaturation

When a solution contains as much solute as it can at a given temperature.

UnsaturatedUnsaturated Can still dissolve more.

SaturatedSaturated Have dissolved all you can.

SupersaturatedSupersaturated Temporarily have dissolved

too much.

PrecipitatePrecipitate Excess solute that falls out of solution.

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ConcentrationConcentration

M = moles solute molliters of solution L

=

MolarityMolarity• M - special symbol which means molar ( mol/L )

• Recognizes that compounds have differentformula weights (or molar masses). Easy for calculating number of moles in volume used.

• A 1 M solution of magnesium atoms contains thesame number of molecules as 1 M Hydrochloric acid.

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MolarityMolarity

M = moles solute molliters of solution L

=

MolarityMolarity

M - special symbol which means molar ( mol/L ) •Recognizes that compounds have different

formula weights.

• A 1 M solution of hydrochloric acid contains 1 mole of HCl in each liter of solution

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MolarityMolarity

Calculate the molarity of 2.0 L solution that contains 10 moles of NaOH.

Use definition of Molarity:MNaOH= moles /liter

Plug in data from problem:

MNaOH= 10 molNaOH / 2.0 L

Calculate answer: MNaOH = 5.0 M

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MolarityMolarity

What’s the molarity of a solution that has 18.23 g HCl in 2.0 liters?

First, you need the molar mass of HCl.First, you need the molar mass of HCl.Molar MassHCl = 1.008 x 1 H + 35.45 x 1

Cl= 36.46 g = 1

mol

Next, find the number of moles.Next, find the number of moles.molesHCl = 18.23 gHCl x ( 1mol )

36.46 g= 0.50 mol

Finally, divide by the volume.Finally, divide by the volume.MHCl = 0.50 mol / 2.0 L

= 0.25 M

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Solution stoichiometrySolution stoichiometry

Extension of earlier stoichiometry problems.Extension of earlier stoichiometry problems.

First step is to determine the number of moles based on solution concentration and volume.

Final step is to convert back to volume or concentration as required by the problem.

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Solution stoichiometry Solution stoichiometry exampleexample

Determine the volume of 0.100 M HCl that contains 5.60 grams of HCl.

The first step is to determine how many moles of NaOH we have.

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We have 5.60 grams of a HCl. This is the starting point. (The 0.100 M is actually a conversion factor!)

Start your set up….this should look familiar:

5.60 grams HCl x ( ____________) x (___________)=

What unit do we want to cancel? What fact might we need?

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5.60 grams HCl x ( ____________) x (___________)= g HClMolar Mass:1 mol = sum masses in gramsHCl H 1 x 1.008 = 1.008 Cl 1x 35.45 = 35.45

36.458g HCl = 1mol HCl

5.60 grams HCl x ( __1mol HCl__) x (___________)= 36.458g HCl

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5.60 grams HCl x ( __1mol HCl__) x (___________)= 36.458g HCl

What’s next? Reread problem:Determine the volume of 0.100 M HCl that contains 5.60 grams of HCl.

Cancel out moles and go to liters, right?

5.60 grams HCl x ( __1mol HCl__) x (___L HCl___)= 36.458g HCl mol HCl

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5.60 grams HCl x ( __1mol HCl__) x (___L HCl___)= 36.458g HCl mol HCl

We can’t use 1mol =22.4L because it’s not a gas!

However, we CAN use the MOLARITY as aconversion factor because M= (mol)

L

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0.100 M HCl means 0.100 mol HCl are in every1 L.

This is a conversion factor 0.100 mol HCl = 1L HCl for this 0.100 M solution of HCL

5.60 grams HCl x ( __1mol HCl__) x (_0.100_L HCl__)= 36.458g HCl 1 mol HCl

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Solution stoichiometry Solution stoichiometry problems:problems:

How many grams of CaCl2 are needed to make 0.250 L of a 4 M CaCl2 solution?

How many molecules are in 25 L of 1.25 M solution of ethanol?

What volume of 6 M H2SO4 is needed to get 75 g of H2SO4?

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Acids, bases and saltsAcids, bases and salts

Three types of compounds are electrolytes:

• AcidAcid - a compound that increases the concentration of hydrogen ions in water.

HCl H+ + Cl-

• BaseBase - a compound that increases the concentration of hydroxide ion in water.

NaOH Na+ + OH-

• SaltSalt - the ions that remain after an acid and base react with each other - neutralization.

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

water

water

water

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UsesUses

•H3PO4 - soft drinks, fertilizer, detergents

•H2SO4 - fertilizer, car batteries

•HCl - gastric juice

•HC2H3O2 - vinegar

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UsesUses

•NaOH - lye, drain and oven cleaner

•Mg(OH)2 - laxative, antacid

•NH3 - cleaners, fertilizer

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PropertiesProperties

•sour taste

•corrosive

•electrolytes

•turn litmus red

•react with metals to form H2 gas

•bitter taste

•corrosive

•electrolytes

•turn litmus blue

•slippery feel

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AcidsAcids

þProduce H+ (as H3O+) ions in water

þProduce a negative ion (-) too

þTaste sour

þCorrode metals

þReact with bases to form salts and

water

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ACID:ACID:

• AcidsAcids– Ionize to form hydronium ions (H3O+) in

water

HCl + H2O H3O+ + Cl–

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BasesBases

Produce OH- ions in water

Taste bitter, chalky

Are electrolytes

Feel soapy, slippery

React with acids to form salts and

water

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Bases:Bases:

• BasesBases–Dissociate or ionize to form hydroxide ions (OH-) in water

NH3 + H2O NH4+ + OH-

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Arrhenius Acids and BasesArrhenius Acids and Bases

Acids produce H+ in aqueous solutions

waterHCl H+(aq) + Cl- (aq)

Bases produce OH- in aqueous solutions

water

NaOH Na+(aq) + OH-

(aq)

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Arrhenius Acids and BasesArrhenius Acids and Bases

Acids ionize H+ in aqueous solutions water

HCl H+(aq) + Cl- (aq)

Bases dissociate OH- in aqueous solutions

water

NaOH Na+(aq) + OH-

(aq)

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Bronsted-Lowry AcidsBronsted-Lowry Acids

Acids are hydrogen ion (H+) donorsBases are hydrogen ion (H+) acceptors

HCl + H2O H3O+ + Cl-

donor acceptor + -

+ +

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Some acids, bases and their saltsSome acids, bases and their salts

AcidAcid Sodium salt Sodium saltNameName FormulaFormula NameName FormulaFormulaAcetic acid HC2H3O2 Sodium acetate NaC2H3O2

Hydrogen chloride HCl Sodium chloride NaClNitric acid HNO3 Sodium nitrate

NaNO3

Phosphoric acid H3PO4 Sodium phosphate Na3PO4

Sulfuric acid H2SO4 Sodium sulfate Na2SO4

BaseBase Chloride salt Chloride saltNameName FormulaFormula NameName FormulaFormulaSodium hydroxide NaOH Sodium chloride NaClBarium oxide BaO Barium chloride BaCl2Sodium oxide Na2O Sodium chloride NaClAmmonia NH3 Ammonium chloride NH4Cl

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Some acids, bases and their saltsSome acids, bases and their saltsDO NOT dissociate completely.DO NOT dissociate completely.

Their strength is expressedTheir strength is expressed

Weak AcidWeak AcidNameName FormulaFormulaAcetic acid HC2H3O2

Weak BaseWeak BaseNameName FormulaFormula

Ammonia NH3

KKaa is the is the

ionization ionization constant for constant for acids:acids:

It tells the It tells the strengthstrength

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Weak Electrolytes in HWeak Electrolytes in H22OO

Weak electrolytes only dissociate or ionize slightly.

These charged particles act as a conductor and can transfer electricity, but there are not as many of them.

HC2H3O2(l) H+(aq) + C2H3O2

-(aq)

For weak electrolytes, this is reversible and in equilibrium.

Some acids and some bases are weak electrolytes; their

strength is represented by Ka or by Kb

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•Arrhenius ConceptAcids: H+ donorsBases: OH- donors

Bronsted-Lowry conceptAcids: H+ donorsBases: H+ acceptors

Lewis conceptAcids: electron pair acceptorsBases: electron pair donors

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IndicatorsIndicators

• IndicatorIndicator–substance that changes color in an acid or base

• ExamplesExamples::– litmus - red/blue–phenolphthalein - colorless/pink–goldenrod - yellow/red–red cabbage juice - pink/green

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Indicators and pH RangesIndicators and pH Ranges

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Indicator examplesIndicator examples

Acid-base indicators are weak acids that undergo a color change at a known pH.

phenolphthalein

pH

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Indicator examplesIndicator examples

methyl red

bromthymol blue

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Defining IndicatorsDefining Indicators

• Most solutions of acids or bases are clear and colorless. Therefore they cannot be distinguished from ordinary water by appearance alone.

• The simplest way to distinguish them from water is to use an indicator. A pH meter can also be used.

• An indicator is a chemical that changes colour as the concentration of H+ (aq) or OH– (aq) changes.

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Defining Indicators (con’t)Defining Indicators (con’t)

• Two of the most common indicators are phenolphthalein and litmus.

• Litmus is a compound that is extracted from lichens, a plant-like member of the fungi kingdom. Litmus paper is made by dipping paper in litmus solution.

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NeutralizationNeutralization

The reaction of an acid with a base to produce a salt and water.

HBr (aq) + LiOH (aq) LiBr (aq) + H2O (l)

If we prepare a standard solution of LiOH, we can then use it to determine the concentration of HBr in a sample.

This is an example of Analytical Chemistry.

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TitrationTitration

Method based on measurement of volume.

•You must have a solution of known concentration - standard solution.standard solution.

•It is added to an unknown solution while the volume is measured.

•The process is continued until the end end pointpoint is reached - a change that we can measure.

•Acids and bases are commonly measured using titrations.

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TitrationsTitrations

BuretBuret - volumetric glassware used for titrations.

It allows you to add a known amount of your titrant to the solution you are testing.

An indicator will give you the endpoint.

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Note the color change which indicates that the ‘endpoint’ has been reached.

Start End

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Essential Questions:

Enduring Understandings:

Knowledge and Skills:

What quantities do scientist use to express solubility?

Molarity is a measure of concentration commonly used. Parts per million (ppm) also is used.

Express concentrations of solutions quantitatively.

Why does something dissolve?

The structure of matter determines whether solutions form.

Define solubility and the factors that affect it.

Can an unlimited amount of a substance dissolve in H2O?

Solubility limits vary based on the substance and temperature.

Use a solubility curve to make predictions about a solution.

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4 - 1 Aqueous Solutions. 4 - 2 Essential Questions: Why does something dissolve? Can an unlimited quantity of a substance dissolve in H 2 O? What quantities