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Reactions in SolutionReactions in Solution

Some Important DefinitionsSome Important Definitions

ElectrolytesElectrolytes

Reactions in SolutionReactions in Solution

Ionic EquationsIonic Equations

Single Replacement ReactionsSingle Replacement Reactions

ConcentrationConcentration

Solution StoichiometrySolution Stoichiometry

TitrationsTitrations

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Sugar in waterOxygen in water

AirDental fillings

Saline

Sugar in waterOxygen in water

AirDental fillings

Saline

SolutionsSolutions

A solutionA solution A homogeneous mixture of twoor more components.

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A solutionA solution

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

A solution consists of two component types.

solventsolvent - component in the greater extent

solutesolute - component in the lesser extent(You may have more than one.)

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Physical states of solutionsPhysical states of solutions

Solutions can be made that exist in any of the three states.

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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SolubilitySolubility

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

Common unit- grams / 100 ml

Factors affecting solubilityFactors affecting solubility•Temperature•Pressure•Polarity

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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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Properties ofProperties ofaqueous solutionsaqueous solutions

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 compoundsDissolving ionic compounds

When an ionic solid dissolves in water, the solvent removes ions from the crystal.

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Dissolving ionic compoundsDissolving ionic compounds

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Dissolving covalent Dissolving covalent compoundscompounds

Covalent compounds do not dissociate.

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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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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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Reactions between ions in solutionReactions between ions in solution

Neutralization is an example of a reaction between ions in solution.

When ions react, we might observe the formation of a precipitate or a gas.AgNO3 (aq) + NaCl (aq) AgCl AgCl (s)(s) + NaNO3 (aq)

Na2CO3 (aq) + 2HNO3 (aq) 2NaNO3 (aq) +H2O (l) CO CO2 2 (g)(g)

However, not all ions will react in solution.

KNO3 (aq) + NaCl (aq) No reaction

Solubility rules can help predict reactions.

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Some simple solubility rulesSome simple solubility rules

• All acids are soluble.

• All Na+, K+ and NH4+ salts are soluble.

• All nitrate and acetate salts are soluble.

• All chlorides except AgCl and Hg2Cl2 are soluble. PbCl2 is slightly soluble.

• All sulfates are soluble except PbSO4, Hg2SO4, SrSO4 and BaSO4. Ag2SO4 and CaSO4 are slightly soluble.

• All sulfides are insoluble except those of the Group IA (1), IIA (2) and ammonium sulfide.

• All hydroxides are insoluble except those of the group IA(1) and Ba(OH)2. Sr(OH)2 and Ca(OH)2 are slightly soluble.

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Ionic equationsIonic equations

When ionic substances dissolve in water, they dissociate into ions.

AgNO3 Ag+ + NO3

-

KCl K+

+ Cl-

When a reaction occurs, only some of the ions are actually involved in the reaction.

AgAg++ + NO3

- + K

+ + ClCl- AgClAgCl(s(s) + K+ +

NO3-

H2O

H2O

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Ionic equationsIonic equations

To help make the reaction easier to see, we commonly list only the species actually involved in the reaction.

Full ionic equationFull ionic equation

AgAg++ + NO3

- + K

+ + ClCl- AgCAgCll(s)(s) + K+ + NO3

-

Net ionic equationNet ionic equationAgAg++

+ ClCl-- AgClAgCl(s)(s)

NO3- and K

+ are referred to as spectatorspectator ions.

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Single replacement reactionSingle replacement reaction

Where one element displaces another in a chemical compound.

H2 + CuO Cu + H2O

• In this example, hydrogen replaces copper.

• This type of reaction always involves oxidation and reduction (REDOX).

• Since one species is replacing another, there are no spectator ions.

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Single replacement reactionsSingle replacement reactions

If various metals are in water, we observe that some are more reactive than others.

2Na (s) + 2H2O (l) 2NaOH (aq) + H2 (g) (fast)

Ca (s) + 2H2O (l) Ca(OH)2 (s) + H2 (g) (slow)

Mg (s) + H2O (l) no reaction

This indicates that the order of reactivity of these metals towards water is

Na > Ca > MgNa > Ca > Mg

We can show the reactivity of metals towards water and acids using an activity series.activity series.

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Activity series of metalsActivity series of metalspotassium

sodiumpotassium

sodium

calciumcalcium

magnesiumaluminum

zincchromium

magnesiumaluminum

zincchromium

ironnickel

tinlead

ironnickel

tinlead

coppersilver

platinumgold

coppersilver

platinumgold

incr

easi

ng r

eact

ivit

y

Reacts violently with cold water

Reacts slowly with cold water

Reacts very slowly with steambut quite reactive in acid

Reacts moderately with acid

Unreactive in acid

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Activity series of metals -Activity series of metals -various metals in HClvarious metals in HCl

Iron Zinc Magnesium

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Reactivity of nonmetalsReactivity of nonmetals

I

BrSe

ClS

FO

P

NC

Increased reactivity

Incr

ease

d r

eact

ivit

y

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Concentration of solutionsConcentration of solutions

We need a way to tell how much solute is in a solution - concentrationconcentration.

There are many systems - we will cover four.

•Weight / volume percent•Volume / volume percent•Weight / weight percent•Molarity

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Weight/Volume %Weight/Volume %

Weight/Volume % = Mass solute Total Volume

x 100

If 5 grams of NaCl is dissolved in water to make 200 ml of solution, what is the concentration?

5 g / 200 ml * 100 = 2.5 wt/v%

Saline is a 0.9 wt/v% solution of NaCl in water.

use g and mluse g and ml

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Volume/Volume %Volume/Volume %

Volume/Volume % = Volume SoluteTotal Volume

x 100

If 10 ml of alcohol is dissolved in water to make 200 ml of solution, what is the concentration?

10 ml / 200 ml * 100 = 5 V/V%

Alcohol in wine is measured as a V/V%.

Use the same units for bothUse the same units for both

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Weight/Weight %Weight/Weight %

Weight/Weight % = Mass SoluteTotal Mass

x 100

If a ham contained 5 grams of fat in 200 gof ham, what is the % wt/wt?

5 g / 200g * 100 = 2.5 wt/wt%

On the label, it would say 97.5 % fat free.

Use the same units for bothUse the same units for both

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Very low concentrationsVery low concentrations

Pollutants in air and water are typically found at very low concentrations. Two common units are used to express these trace amounts.

Parts per million - ppmParts per million - ppmParts per billion - ppbParts per billion - ppb

Both are modifications of the % system which could be viewed as parts per hundred - pph.

Both mass and volume % systems are used.

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Low concentrations in airLow concentrations in air

Trace amounts in are are expressed as volume/volume ratios.

ppm = x 106

ppb = x 109

Example.Example. One cm3 of SO2 in one m3 of air would be expressed as 1 ppm or 1000 ppb.

volume solutevolume solution

volume solutevolume solution

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Low concentrations in waterLow concentrations in water

Mass percentages are used for water pollutants.

ppm = x 106

ppb = x 109

Example.Example. One ppm of a toxin in water is the same as 1 mg / liter since one liter of water has a mass of approximately 106 mg.

mass solutemass solution

mass solutemass solution

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MolarityMolarity

M = moles solute molliters of solution L

=

MolarityMolarity• Recognizes that compounds have different

formula weights.

• A 1 M solution of glucose contains thesame number of molecules as 1 M ethanol.

• [ ] - special symbol which means molar ( mol/L )

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MolarityMolarity

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

MNaOH = 10 molNaOH / 2.0 L

= 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 FM of HCl.First, you need the FM of HCl.FMHCl = 1.008 x 1 H + 35.45 x 1 Cl

= 36.46 g/mol

Next, find the number of moles.Next, find the number of moles.molesHCl = 18.23 gHCl / 36.46 g/mol

= 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 preparationSolution preparation

Solutions are typically prepared by:

Dissolving the proper amount of solute and diluting to volume.

Dilution of a concentrated solution.

Lets look at an example of the calculations required to prepare known molar solutions using both approaches.

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Making a solutionMaking a solution

You are assigned the task of preparing 100.0 ml of a 0.5000 M solution of sodium chloride.

What do you do?

First, you need to know how many moles of NaCl are in 100.0 ml of a 0.5 M solution.

mol = M x V (in liters)

= 0.5000 M x 0.1000 liters

= 0.05000 moles NaCl

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Making a solutionMaking a solution

Next, we need to know how many grams of NaCl to weigh out.

gNaCl = mol x FMNaCl

= 0.05000 mol x 58.44 g/mol

= 2.922 grams

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Making a solutionMaking a solution

Finally, you’re ready to make the solution.

Weigh out exactly 2.922 grams of dry, pure NaCl and transfer it to a volumetric flask.

Fill the flask about 1/3 of the way with pure water and gently swirl until the salt dissolves.

Now, dilute exactly to the mark, cap and mix.

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DilutionDilution

Once you have a solution, it can be diluted by adding more solvent. This is also important for materials only available as solutions

M1V1 = M2V2

1 = initial 2 = final

Any volume or concentration unit can be used as long as you use the same units on both sides of the equation.

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DilutionDilution

What is the concentration of a solution produced by diluting 100.0 ml of 1.5 MNaOH to 2.000 liters?

M1V1 = M2V2

M1 = 1.5 M M2 = ???V1 = 100.0 ml V2 = 2000 ml

M2 = M1V1 / V2

M2 = (1.5 M) (100.0 ml) = 0.075 M (2000. ml)

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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.

You still need a balanced equation and must use the coefficients for working the problem.

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Solution stoichiometry Solution stoichiometry exampleexample

Determine the volume of 0.100 M HCl that must be added to completely react with 250 ml of 2.50 M NaOH

Balanced chemical equationBalanced chemical equation

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

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

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Solution stoichiometry Solution stoichiometry exampleexample

We have 250 ml of a 2.50 M solution.

molNaOH = 0.250 L x 2.50 mol/L

= 0.625 molNaOH

From the balanced chemical equation, we know that we need one mole of HCl for each mole of NaOH.

That means we need 0.625 molHCl.

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Solution stoichiometry exampleSolution stoichiometry example

Now we can determine what volume of our 0.100 M HCl solution is required.

L = molHCl / MHCl

= 0.625 mol

= 6.26 L

1 L0.100 mol( )

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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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NeutralizationNeutralization

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

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

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

This is an example of Analytical Chemistry.

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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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TitrationsTitrations

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TitrationsTitrations

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

Start End

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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