types of chemical reactions and solution stoichiometry

Types of Chemical Types of Chemical ReactionsReactions

and Solution and Solution StoichiometryStoichiometry

Classification of MatterClassification of MatterSolutions are homogeneous mixtures

SoluteSoluteA solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

SolvenSolventt

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

Saturation of SolutionsSaturation of Solutions A solution that contains the maximum A solution that contains the maximum

amount of solute that may be dissolved amount of solute that may be dissolved under existing conditions is under existing conditions is saturatedsaturated. .

A solution that contains less solute than A solution that contains less solute than a saturated solution under existing a saturated solution under existing conditions is conditions is unsaturatedunsaturated. .

A solution that contains more dissolved A solution that contains more dissolved solute than a saturated solution under solute than a saturated solution under the same conditions is the same conditions is supersaturatedsupersaturated..

The ammeter measures the flow of electrons (current) through the circuit.

If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

Electrolytes vs. Electrolytes vs. NonelectrolytesNonelectrolytes

An electrolyte is:

A substance whose aqueous solution conducts an electric current.

A nonelectrolyte is:

A substance whose aqueous solution does not conduct an electric current.

Try to classify the following substances as electrolytes or nonelectrolytes…

Definition of Electrolytes and Definition of Electrolytes and NonelectrolytesNonelectrolytes

1.Pure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution 5.Hydrochloric acid solution 6.Lactic acid solution 7.Ethyl alcohol solution 8.Pure, solid sodium chloride

Electrolytes?Electrolytes?

ELECTROLYTES: NONELECTROLYTES:

  Tap water (weak)   NaCl solution   HCl solution   Lactate solution

(weak)

  Pure water   Sugar solution   Ethanol

solution   Pure, solid

NaCl

But why do some compounds conduct electricity in solution while others do not…?

Answers…Answers…

Ionic Compounds DissociateIonic Compounds Dissociate

NaCl(s)

AgNO3(s) MgCl2(s)

Na2SO4(s)

AlCl3(s)

Na+(aq) + Cl-(aq)

Ag+(aq) + NO3-(aq)

Mg2+(aq) + 2 Cl-(aq)

2 Na+(aq) + SO42-

(aq)Al3+(aq) + 3 Cl-(aq)

The reason for this is the polar nature of the water molecule…

Positive ions associate with the negative end of the water dipole (oxygen).Negative ions associate with the positive end of the water dipole (hydrogen).

Ions tend to stay in solution where they canconduct a current rather than re-forming a solid.

Covalent acids form ions in solution, with the help of the water molecules.

For instance, hydrogen chloride molecules, which are polar, give up their hydrogens to water, forming chloride ions (Cl-) and hydronium ions (H3O+).

Some covalent compounds IONIZE in solution

Other examples of strong acids include:

Sulfuric acid, H2SO4

Nitric acid, HNO3

Hydriodic acid, HI Perchloric acid, HClO4

Hydrobromic acid, HBr Chloric acid, HClO3

Periodic acid, HIO4

Strong acids such as HCl are completelyionized in solution.

Many of these weaker acids are “organic” acids that contain a “carboxyl” group.

The carboxyl group does not easily give up its hydrogen.

Weak acids such as lactic

acid usually ionize less than 5% of the time.

Other organic acids and their sources include:

o Citric acid – citrus fruit o Malic acid – apples o Butyric acid – rancid butter o Amino acids – protein o Nucleic acids – DNA and RNA o Ascorbic acid – Vitamin C

This is an enormous group of compounds; these are only a few examples.

Because of the carboxyl group, organic acids are

sometimes called “carboxylic acids”.

Sugar (sucrose – C12H22O11),

and ethanol (ethyl alcohol – C2H5OH) do not ionize - That is why they are nonelectrolytes!

However, most covalent compounds do not ionize

at all in solution.

MolarityMolarity

The concentration of a solution measured in moles of solute per liter of solution.

mol = M L

Preparation of Molar Preparation of Molar SolutionsSolutions

Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution?

Step #1: Ask “How Much?” (What volume to prepare?)

1.500 L

Step #2: Ask “How Strong?” (What molarity?)

0.500 mol

1 L

Step #3: Ask “What does it weigh?” (Molar mass is?)

58.44 g

1 mol= 43.8 g

Serial DilutionSerial Dilution

It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution.

Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution?

MstockVstock = MdiluteVdilute

(11.6 M)(x Liters) = (3.0 M)(0.250 Liters)

x Liters = (3.0 M)(0.250 Liters) 11.6 M

= 0.065 L

Single Replacement Reactions

Replacement of:

Metals by another metal Hydrogen in water by a metal Hydrogen in an acid by a metal Halogens by more active halogens

A + BX AX + B

BX + Y BY + X

The Activity Series of the Metals

   Lithium    Potassium    Calcium    Sodium    Magnesium    Aluminum    Zinc    Chromium    Iron    Nickel    Lead    Hydrogen Hydrogen    Bismuth    Copper    Mercury    Silver    Platinum    Gold

Metals can replace other metals provided that they are above the metal that they are trying to replace.

Metals above hydrogen can replace hydrogen in acids.

Metals from sodium upward can replace hydrogen in water

The Activity Series of the Halogens

  Fluorine   Chlorine   Bromine   Iodine

Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace.

2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)

MgCl2(s) + Br2(g) ???No Reaction

???

Double Replacement Reactions

The ions of two compounds exchange places in an aqueous solution to form two new compounds.

AX + BY AY + BX

One of the compounds formed is usually a precipitate (an insoluble solid), an insoluble gas that bubbles out of solution, or a molecular compound, usually water.

Double replacement forming a precipitate…

Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

Pb2+(aq) + 2 NO3-(aq) + 2 K+(aq) +2 I-(aq) PbI2(s) + 2K+(aq) + 2

NO3-(aq)

PbPb2+2+(aq) + 2 I(aq) + 2 I--(aq) (aq) PbIPbI22(s)(s)

Double replacement (ionic) equation

Complete ionic equation shows compounds as aqueous ions

Net ionic equation eliminates the spectator ions

Solubility Rules – Mostly Solubility Rules – Mostly SolubleSoluble

Solubility Rules – Mostly Solubility Rules – Mostly SolubleSolubleIonIon SolubilitSolubilit

yyExceptionsExceptions

NONO33-- SolubleSoluble NoneNone

ClOClO44-- SolubleSoluble NoneNone

NaNa++ SolubleSoluble NoneNone

KK++ SolubleSoluble NoneNone

NHNH44++ SolubleSoluble NoneNone

ClCl--, I, I-- SolubleSoluble PbPb2+2+, Ag, Ag++, Hg, Hg222+2+

SOSO442-2- SolubleSoluble CaCa2+2+, Ba, Ba2+2+, Sr, Sr2+2+, Pb, Pb2+2+, Ag, Ag++, ,

HgHg2+2+

Solubility Rules – Mostly Solubility Rules – Mostly InsolubleInsoluble

IonIon SolubilitSolubility y

ExceptionsExceptions

COCO332-2- InsolubleInsoluble Group IA and NHGroup IA and NH44

++

POPO443-3- InsolubleInsoluble Group IA and NHGroup IA and NH44

++

OHOH-- InsolubleInsoluble Group IA and CaGroup IA and Ca2+2+, Ba, Ba2+2+, , SrSr2+2+

SS2-2- InsolubleInsoluble Groups IA, IIA, and NHGroups IA, IIA, and NH44++

Oxidation and Reduction (Redox)Oxidation and Reduction (Redox)

Electrons are transferred

  Spontaneous redox rxns can transfer energy

  Electrons (electricity)   Heat

Non-spontaneous redox rxns can be made to happen with electricity

Oxidation and ReductionOxidation and Reduction

GGainain EElectronslectrons = = RReductioneduction

An old memory device for An old memory device for oxidation and reduction goes oxidation and reduction goes like this…like this… LEOLEO says says GERGER

LLoseose EElectronslectrons = = OOxidationxidation

Oxidation Reduction ReactionsOxidation Reduction Reactions(Redox)(Redox)

11

2

00

22

ClNaClNaEach sodium atom loses one electron:

Each chlorine atom gains one electron:

eNaNa10

10 CleCl

LEO says GERLEO says GER : :

eNaNa10

Lose Electrons = Oxidation

Sodium is oxidized

Gain Electrons = Reduction

10 CleCl Chlorine is reduced

Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers

Rules 1 & 2Rules 1 & 2

1. The oxidation number of any uncombined element is zero

2. The oxidation number of a monatomic ion equals its charge

11

2

00

22

ClNaClNa

Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers

Rules 3 & 4Rules 3 & 4

3. The oxidation number of oxygen in compounds is -24. The oxidation number of hydrogen in compounds is +1

2

2

1

OH

Rules for Assigning Oxidation Rules for Assigning Oxidation Number Rule 5Number Rule 5

5. The sum of the oxidation numbers in the formula of a compound is 02

2

1

OH2(+1) + (-2) = 0 H O

2

122

)(

HOCa(+2) + 2(-2) + 2(+1) = 0 Ca O H

Rules for Assigning Oxidation Rules for Assigning Oxidation NumbersNumbers

Rule 6Rule 66. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge

3

2?

ONX + 3(-2) = -1 N O

24

2?

OS

X = +5 X = +6

X + 4(-2) = -2 S O

Reducing Agents and Oxidizing Reducing Agents and Oxidizing AgentsAgents

  The substance reduced is the oxidizing agent   The substance oxidized is the reducing agent

eNaNa10

10 CleCl

Sodium is oxidized – it is the reducing agent

Chlorine is reduced – it is the oxidizing agent

Trends in Oxidation and ReductionTrends in Oxidation and Reduction

Active metals:   Lose electrons

easily   Are easily

oxidized   Are strong

reducing agents Active nonmetals:   Gain electrons easily   Are easily reduced   Are strong oxidizing agents

Redox Reaction Prediction #1

Important Oxidizers Formed in reaction

MnO4- (acid

solution) MnO4-

(basic solution) MnO2 (acid solution) Cr2O7

2- (acid) CrO4

2- HNO3, concentrated HNO3, dilute H2SO4, hot conc Metallic Ions

Free Halogens HClO4

Na2O2

H2O2

Mn(II) MnO2

Mn(II) Cr(III) Cr(III) NO2

NO SO2

Metallous Ions Halide ions Cl-

OH-

O2

Redox Reaction Prediction #2

Important Reducers Formed in reaction

Halide IonsFree MetalsMetalous Ions Nitrite Ions Sulfite IonsFree Halogens (dil, basic sol) Free Halogens (conc, basic sol) C2O4

2-

Halogens Metal Ions Metallic ions Nitrate Ions SO42- Hypohalite ions Halate ions CO2

Not All Reactions are Redox Not All Reactions are Redox ReactionsReactions

Reactions in which there has been no change in oxidation number are not redox rxns.

Examples:

)()()()( 3

2511111

3

251

aqONNasClAgaqClNaaqONAg

)()()()(22

2

1

4

26

2

1

4

26

2

1121

lOHaqOSNaaqOSHaqHONa