Chemical ReactionsChemical Reactions

Goals:

1. Write balanced equations for simple chemical reactions.

2. Understand the nature of ionic compounds dissolved in water.

3. Recognize common acids and bases and understand their behavior in aqueous solution.

4. Recognize and write equations for the common types of reactions in aqueous solution and net-ionic equations.

5. Recognize common oxidizing and reducing agents and identify oxidation-reduction reactions.

Chemical ReactionsChemical Reactions

• A stream of chlorine gas is directed onto solid phosphorus.

• The mixture bursts into flame, and a chemical reactions produces liquid phosphorus trichloride.

What are Chemical Equations?What are Chemical Equations?

Depict the kind of reactants and products and their relative amounts in a reaction.

P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)

The numbers in the front are called

stoichiometric coefficients.The letters (s), (g), and (l) are the

physical states of compounds.

reactants products

Chemical EquationsChemical Equations

P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)

This equation means1 molecule of solid phosphorus (P4) reacts with 6 molecules of chlorine gas producing 4 molecules of phosphorus trichloride.

or___ mol of phosphorus reacts with ___ moles of chlorine producing ___ moles of phosphorus trichloride.

What is the Law of What is the Law of Conservation of Matter?Conservation of Matter?

• Because the same atoms are present in a reaction at the beginning and at the end, the amount of matter in a system does not change.

• Because of the principle of the Because of the principle of the conservation of matter, an conservation of matter, an equation must be balanced.equation must be balanced.It must have the same number It must have the same number of atoms of the same kind on of atoms of the same kind on both sides.both sides. Lavoisier, 1788Lavoisier, 1788

Law of Conservation of Law of Conservation of MatterMatter

We must lay it down as an incontestable axiom, that in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment. …. Upon this principle, the whole art of performing chemical experiments depends.– Lavoisier’s Traité Élémentaire de Chimie.

Law of Conservation of Matter Law of Conservation of Matter and Chemical Equationsand Chemical Equations

P4 (s) + 6 Cl2 (g) - - - > 4 PCl3 (l)

• The numbers in front of each formula – stoichiometric coefficients - in a balanced chemical equation are required by the law of conservation of matter.

Students should become familiar with writing and balancing chemical

equations.

6 x 2 = 12 Cl atoms4 x 3 = 12 Cl atoms

4 P atoms 4 P atoms

Write a reaction for Iron reacting with Chlorine producing Iron (III) chloride

Notice the Notice the stoichiometric stoichiometric coefficientscoefficients and the physical and the physical states of the reactants and states of the reactants and

products.products.

Visualizing Chemical Visualizing Chemical ReactionsReactions

• The reaction between reactant A (red) and reactant B (blue) is shown in the diagram:

Based on this diagram, which equation best describes the reaction?

a) A2 + B A2B b) 2 A + B4 2 AB2

c) A2 + 4 B 2 AB2 d) A + B2 AB2

What is an Aqueous What is an Aqueous Solution?Solution?

• Aqueous solution:Aqueous solution: an homogenous mixture where the solvent is water.

KMnOKMnO44 in water in water KK++(aq) + MnO(aq) + MnO44--(aq)(aq)

How can Water be a solvent for How can Water be a solvent for Ionic Compounds?Ionic Compounds?

Water is a polar molecule: it has a ___________ (one side of the molecule is +, the other is -).This is due to the difference in _________________ (the ability of an atom in a molecule to attract electrons to itself) between oxygen and hydrogen.

O is more electronegative than H: O appears partially ________ charged (), and H partially __________ charged (+).

How do we know ions are How do we know ions are present in aqueous present in aqueous

solutions?solutions?The solutions The solutions conduct _______________!!

The The substances that provide ions in an aqueous solution are calledare called ____________________________________..

HCl, CuClHCl, CuCl22, and NaCl are, and NaCl are_____ _________. _____ _________.

What is a Strong Electrolyte?What is a Strong Electrolyte?

They They ionizeionize or or dissociatedissociate completely completely (or nearly so) into (or nearly so) into ionsions..

HCl, CuClHCl, CuCl22, and NaCl are , and NaCl are strong strong electrolytes.electrolytes.

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

What is a Weak Electrolyte?What is a Weak Electrolyte?

Acetic acid ionizes only to a small extent, so it is a

weak electrolyte.weak electrolyte.CH3CO2H(aq)

CH3CO2-(aq) +

H+(aq)

What is a Nonelectrolyte?What is a Nonelectrolyte?

Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes.nonelectrolytes.Examples include:Examples include:

sugarsugarethanolethanol

ethylene glycolethylene glycol

Summary of the Electrolytic Summary of the Electrolytic BehaviorBehavior

of Common of Common Soluble IonicSoluble Ionic and andMolecular CompoundsMolecular Compounds

Strong Weak Electrolyte Electrolyte

Nonelectrolyte

Ionic

Molecular

All

All others

None

Strong acids

None

Weak acidsandWeak bases(NH3)

Which Ionic Compounds are Which Ionic Compounds are Soluble in Water?Soluble in Water?

If one ion from the “Soluble If one ion from the “Soluble Compd.” list is present in a Compd.” list is present in a

compound, the compound is compound, the compound is water soluble.water soluble.

Book Ed 7:

Figure 3.10 (p. 126)

Book Ed 6:

Figure 5.3 (p. 179)

Learn this

table!

Solubility of Ionic Solubility of Ionic CompoundsCompounds

What is an Acid?What is an Acid?

An acid - - -> HAn acid - - -> H++ (in (in water)water)

Some Some strongstrong acidsacids(completely ionized) are:(completely ionized) are:HClHCl hydrochlorichydrochloric

HH22SOSO44 sulfuricsulfuric

HClOHClO44 perchloricperchloric

HNOHNO33 nitricnitric

HNOHNO33

PROTONBecause a hydrogen atom is one proton and one electron, a hydrogen ion (H+) is simply a proton.

What is an Acid?What is an Acid?

An acid ---> HAn acid ---> H++ in water in waterAn acid ---> HAn acid ---> H++ in water in water

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

What is the Hydronium Ion?What is the Hydronium Ion?

HCl

H2O

Cl-

H3O+

hydronium ion

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

Bronsted – Lowry Theory:An acid donates a proton

What is a Weak Acid?What is a Weak Acid?

WEAK ACIDS (only partially WEAK ACIDS (only partially ionizedionized))= weak electrolytes= weak electrolytes

CHCH33COCO22HH acetic acidacetic acid

HH22COCO33 carbonic acidcarbonic acid

HH33POPO44 phosphoric acidphosphoric acidHFHF hydrofluoric acidhydrofluoric acid

CHCH33COCO22H H (aq) H+(aq) + CHCH33COCO22- (aq)

Weak AcidWeak Acid

What is a Base?What is a Base?

Base ---> OHBase ---> OH-- in water in waterBase ---> OHBase ---> OH-- in water in water

NaOH(aq) ---> NaNaOH(aq) ---> Na++(aq) + OH(aq) + OH--

(aq)(aq)

NaOH is NaOH is a a strong strong basebase

HYDROXIDE

How is it that Ammonia, NHHow is it that Ammonia, NH33 is a base?is a base?

Bronsted – Lowry Theory:A base accepts a proton

Acids and BasesAcids and Bases

Students should become familiar with identifying acids and

bases.

Book Ed 7: p. 132

Book Ed 6: p. 187

Representative Trends in Strength of Binary Representative Trends in Strength of Binary Acids (containing only H atoms and a Acids (containing only H atoms and a

nonmetal)nonmetal)

Smaller atom bonded to HShorter bondWeaker acid

Larger atom bonded to HLonger bondStronger acid

Higher electronegativity difference of atoms - more polar bond

baseneutral

weak acid

strong acid

The Bronsted-Lowry TheoryThe Bronsted-Lowry Theory

• 1923 – J. N. Bronsted and T. M. Lowry:

• Acids – a proton (H+) ________.

• Bases – a proton (H+) _________.

HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)

• A reaction between an acid and a base consists of a proton transfer from an acid to a base.

Conjugate PairsConjugate Pairs• The products of an acid-base reaction are also an acid

and a base. The overall reaction consists of two combinations of acids and bases – conjugates pairs.

CH3COOH + H2O CH3COO- + H3O+

• The acid-base conjugate pairs differs in structure only by a proton (H+):– The conjugate acid of a specie is that specie plus _______.– The conjugate base of a specie is that specie minus

__________.

acid (1) base (2) acid (2)base (1)

Conjugate PairsConjugate Pairs

NH3 + H2O NH4+ + OH-

Ammonia (NH3) acts as a base by accepting a proton from H2O. In the reverse reaction, ammonium ion (NH4

+) acts as acid by losing a proton to OH-.

Amphiprotic – a substance that can act ________ __________________________

acid (2)base (1) acid (1) base (2)

Dual Role of WaterDual Role of Water

• Amphiprotic – a substance that can act either as an acid or a base – like H2O.

pair of e- in bond are kept by O atom

lone pair of e- forms new bond

Water EquilibriumWater Equilibrium

• Self-ionization of water: about 1 water molecule in 500 million transfer a proton to another water molecule:

H2O + H2O H3O+ + OH-

• Water is in equilibrium with a hydronium ion and a hydroxide ion (or using our convention with a hydrogen ion and a hydroxide ion).

H2O H+ + OH-

Water EquilibriumWater Equilibrium• Equilibrium lies far to the left (it is mostly

water molecules). Experimentally determined concentrations of ions (25oC) in molarity (moles per liter) are:

[H+] = [OH-] = 1.0 x 10-7 M (= 0.0000001 M)

• Ion product of water (Kw) – product of the concentrations of H+ and OH-, at 25oC is:

Kw = [H+] [OH-] = (1.0 x 10-7) (1.0 x 10-7) = 1.0 x 10-14

• The ion product relationship applies to all aqueous solutions (acids, bases, salts).

What are Basic Oxides?What are Basic Oxides?(Basic Anhydrides)(Basic Anhydrides)

Metal Metal oxides react with water to form bases

CaO(s) + H2O(liq) -- > Ca(OH)2(aq)

CaO in water. Indicator shows solution is basic.

What are Acidic Oxides?What are Acidic Oxides?(Acidic Anhydrides)(Acidic Anhydrides)

NonmetalNonmetal oxides react with water to form acids

CO2(aq) + H2O(l) ---> H2CO3(aq)

SO3(aq) + H2O(l) ---> H2SO4(aq)

And can come from burning coal and oil.

= ACID RAIN

What is a Net Ionic What is a Net Ionic Equation?Equation?

Mg(s) + 2 HCl(aq) --> HMg(s) + 2 HCl(aq) --> H22(g) + MgCl(g) + MgCl22(aq)(aq)

We really should writeWe really should write

Mg(s) + 2 HMg(s) + 2 H++(aq) + 2 Cl(aq) + 2 Cl--(aq) ---> (aq) ---> HH22(g) + Mg(g) + Mg2+2+(aq) + 2 Cl(aq) + 2 Cl--(aq)(aq)

The two Cl- ions are ____________ IONS____________ IONS — they do not participate (could have used NO3

-).We leave the spectator ions out — to write aNET IONIC EQ:

Mg(s) + 2 H+(aq) ---> H2(g) + Mg2+(aq)

Review in Exp 8: Six bottles experiment

Which Which Types of ReactionsTypes of Reactions occur in occur in Aqueous Solution?Aqueous Solution?

• EXCHANGE REACTIONSEXCHANGE REACTIONSThe anions exchange placesbetween cations:

Precipitation

Acid-base; neutralization

Gas-forming

• OXIDATION-REDUCTION REACTIONSOXIDATION-REDUCTION REACTIONSElectron Transfer.

Driving forceFormation of ________

compound Formation of _____ and ______; proton transfer

Evolution of _____________________

What are Precipitation Reactions?What are Precipitation Reactions?

The “driving force” is the The “driving force” is the formation of an insoluble formation of an insoluble compound — a compound — a precipitateprecipitate..

Pb(NOPb(NO33))22(aq) + 2 KI(aq)(aq) + 2 KI(aq)

-----> 2 KNO-----> 2 KNO33(aq) + PbI(aq) + PbI22(s)(s)

Net ionic equation: Net ionic equation:

Net Ionic EquationNet Ionic Equation

Complete formula equation:Complete formula equation:

Pb(NOPb(NO33))2 2 (aq)(aq) + 2 KI + 2 KI (aq)(aq)

-----> 2 KNO-----> 2 KNO3 3 (aq)(aq) + + PbIPbI2 2 (s)(s)

Ionic equation:

Net ionic equation:Net ionic equation:

What are Acid-Base Reactions?What are Acid-Base Reactions?

• The “driving force” is the formation of water.The “driving force” is the formation of water.

NaOH(aq) + HCl(aq) ---> NaCl(aq) + NaOH(aq) + HCl(aq) ---> NaCl(aq) + HH22O(liq)O(liq)

• Net ionic equationNet ionic equation

OHOH--(aq) + H(aq) + H++(aq) ---> H(aq) ---> H22O(liq)O(liq)

This applies to ALL reactions ofThis applies to ALL reactions of

STRONG STRONG acids and bases.acids and bases.

Acid-Base ReactionsAcid-Base Reactions

Complete formula equation:HCl (aq) + NaOH (aq)

Ionic equation:

Net ionic equation:

products do not have characteristics of acid or base.

For strong acids and bases write the ionic form.

Write the equations for ammonia added to Write the equations for ammonia added to phosphoric acid to make ammonium phosphoric acid to make ammonium

phosphate.phosphate.

Complete formula equation:3 NH3 (aq) + H3PO4 (aq)

Ionic equation:

Net ionic equation:

For weak acids and bases do not write the ionic form.

Acid-Base ReactionsAcid-Base Reactions

• Acid-Base reactions are sometimes called

NEUTRALIZATIONS because the solution is

neither acidic nor basic at the end.

• The other product of Acid-Base reactions is a

SALT, with general formula: MX.

HX + MOH ---> MX + H2O

Mn+ comes from base & Xn- comes from acid

This is one way to make compounds!

Salt Water

What are Gas-Forming Reactions?What are Gas-Forming Reactions?

This is primarily the chemistry of metal carbonates.

CO2 and water ---> H2CO3

H2CO3(aq) + Ca2+ ---> 2 H+(aq) +

CaCO3(s) (limestone)

Adding acid reverses this reaction.

MCO3 + acid ---> CO2 + H2O + salt carbonates carbon dioxide

Gas-Forming ReactionsGas-Forming Reactions

CaCO3(s) + H2SO4(aq) --->

2 CaSO4(s) + H2CO3(aq)

Carbonic acid is unstable and forms CO2 & H2O

H2CO3(aq) ---> CO2+ H2O

(Antacid tablethas citric acid + NaHCO3)

PracticePractice

• Write down the complete formula, ionic, and net ionic equations for:Sulfuric acid reacts with calcium carbonate.

Students should become familiar with writing ionic and net

equations.

Gas-Forming ReactionsGas-Forming Reactions

Book Ed 7. p. 140

Book Ed 6: p. 194

Students should become familiar with identifying the several types of

reactions and predicting products of the reactions.

Redox ReactionsRedox Reactions

FuelsFuelsFuelsFuels

CorrosionCorrosionCorrosionCorrosion

BatteriesBatteriesBatteriesBatteries

Manufacturing metalsManufacturing metalsManufacturing metalsManufacturing metals

PhotosynthesisPhotosynthesis

6 CO2 + 6 H2O C6H12O6 + 6 O2

Combustion, respiration/metabolism

C6H12O6 + 6 O2 6 CO2 + 6 H2O

Oxidation and ReductionOxidation and Reduction

• Oxidation is a ________________.• Reduction is a __________________.

LEO says GER

Mg + Cl2 Mg2+ + 2 Cl-

Mg atom _____________; it is __________.

Cl atoms _____________; Cl2 is ___________.

What are Redox Reactions?What are Redox Reactions?

• An oxidation-reduction reaction - must always have both an oxidation and a reduction.Oxidation process – the oxidation number of one or more elements ___________.Reduction process – and the oxidation number of one or more elements _________.

Mg (s) + Cu2+(aq) Mg2+

(aq) + Cu (s)

Half- ReactionsHalf- Reactions

• A redox reaction is two half-reactions that occur simultaneously.

Mg (s) + Cu2+(aq) Mg2+

(aq) + Cu (s)

0 +2 +2 0

Oxidation half-reaction:Mg atoms lose 2 e-

Reduction half-reaction:Cu2+ ions gain 2-

Mg (s) Mg2+(aq) + _____

Cu2+(aq) + _____ Cu (s)

oxidation

reduction

Hydrogen-Oxygen Fuel CellHydrogen-Oxygen Fuel Cell

Hydrogen-Oxygen Fuel CellHydrogen-Oxygen Fuel Cell

• Fuel cellFuel cell - reactants are supplied - reactants are supplied

continuously from an external continuously from an external

source.source.• Cars can use electricity generated Cars can use electricity generated

by Hby H22/O/O22 fuel cells. fuel cells.

• HH22 carried in tanks or generated carried in tanks or generated

from hydrocarbons– (if possible from hydrocarbons– (if possible

solar)solar)

2 H2 + O2 2 H2O

2 H2 4 H+ + 4 e-

O2 + 4 e- 2 O-2

4 H+ + 2 O-2 2 H2O

2 H2 + O2 2 H2O

Identifying Redox ReactionsIdentifying Redox Reactions

• Look for a change in the oxidation number of an element in the course of the reaction.

What are oxidation numbers?

Is the charge an atom has, or appears to have, as determined by the following guidelines for assigning oxidation numbers.Students should become familiar

with assigning OXIDATION NUMBERS – learn the rules.

(Page 200)

Oxidation Numbers in HF: Animation

Follow the Follow the rulesrules for Oxidation Numbers for Oxidation Numbers1. Each atom in a pure element has an oxidation

number of zero. Cu, I2, S8.2. For monoatomic ions, the oxidation number is equal

to the charge on the ion. NaBr, MgBr2.3. Fluorine always has an oxidation number of -1 in

compounds with all other elements.4. Cl, Br, and I always have oxidation number of -1 in

compounds, except when combined with oxygen or fluorine. NaCl, ClO-.

5. The oxidation number of H is +1 and of O is -2 in most compounds. Exceptions: H in a binary compound with a metal, CaH2. O in peroxides can have an oxidation number of -1, H2O2.

6. The algebraic sum of the oxidation numbers for atoms in a neutral compound must be zero; in a polyatomic ion, the sum must be equal to the ion charge. HClO4

Give the Oxidation Number of each Element Give the Oxidation Number of each Element in the following:in the following:

Br2

Na2SO4

CaH2

Fe2O3

P4

H2O2

KMnO4

What is Oxidizing Agent?What is Oxidizing Agent?What is Reducing Agent?What is Reducing Agent?

• OXIDIZING AGENT:The substance that accepts electrons in an oxidation-reduction reaction and gets reduced.

• REDUCING AGENT:The substance that donates electrons in an oxidation-reduction reaction and gets oxidized.

Oxidizing and Reducing AgentsOxidizing and Reducing Agents

K (s) + H2O (l) KOH (aq) + H2 (g)2 2 2

Common Oxidizing and Common Oxidizing and Reducing Agents (Table 5.4, p. Reducing Agents (Table 5.4, p.

203)203)

HNOHNO33 is an is an

oxidizing agentoxidizing agent

2 K + 2 H2 K + 2 H22O --> 2 KOH + HO --> 2 KOH + H22

MetalsMetals (Na, (Na, K, Mg, Fe) K, Mg, Fe) are are reducing reducing agentsagents

Metals Metals (Cu) (Cu) are reducing are reducing agentsagents

Cu + HNOCu + HNO33 --> Cu --> Cu2+2+ + NO + NO22

Students should be familiar with common oxidizing and reducing

agents.

O2, F2, Cl2, Br2, I2, Cr2O2-, MnO4

- H2, Na, K, Fe, Al, C

• Oxygen - Oxidizes coal in electric power plants, gasoline in automobiles, “burns” the food we eat.

• Potassium dichromate - Lab: aldehydes to ketones; ethanol to acetaldehyde.

• Potassium permanganate - Lab: color test for many oxidizable substances (purple color disappears).

• Halogens and Peroxides– Antiseptics – substance applied to living tissue to kill

microorganisms or prevent their growth: Iodine, Hydrogen peroxide (3% sol), Benzoyl peroxide.

– Disinfectants – substance that is applied to nonliving tissue to kill microorganisms: Chlorine from [Ca(OCl)2].

Oxidizing AgentsOxidizing Agents

MnO4- + 5 Fe2+ + 8 H+ Mn2+ + 5 Fe3+ + 4 H2O

Cr2O72- + 3 C2H5OH + 8 H+ 2 Cr3+ + 3 C2H4O + 7 H2O

acetaldehyde

Reducing AgentsReducing Agents• Carbon - To obtain free metals from their ores.

• Metals - To obtain free metals from their ores.

• Hydrogen - To obtain free metals from their ores and to reduce many kinds chemical compounds.

• Organic Compounds– Hydroquinone: it reduces silver ions in photographic films

– Antioxidants – in food chemistryVitamin C (ascorbic acid) prevents the browning of fruit by inhibiting air oxidation.Vitamin E (tocopherol) - Both vitamins retard oxidation reactions that damage

vital components of living cells.

SnO2 (s) + 8 C (s) Sn (s) + CO2 (g)

Cr2O3 (s) + 2 Al (s) Al2O3 (s) + 2 Cr(s)

WO3 (s) + 3 H2 (g) W (s) + 3 H2O

N2 (g) + 3 H2 (g) 2 NH3 (g)Fe

C6H4(OH)2 (aq) + 2 Ag+ (aq) C6H4O2 (aq) + 2 Ag (s) + 2 H+

RememberRemember

• Go over all the contents of your textbook.

• Practice with examples and with problems at the end of the chapter.

• Practice with OWL tutor.• Work on your assignment for OWL

Chapters 4, 5.• Practice with the quiz on CD of

Chemistry Now.