chemical reactions - center for teaching &...

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Chemical Reactions

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Table of Contents: Chemical Reactions

· Balancing Equations

Click on the topic to go to that section

· Types of Chemical Reactions

· Oxidation-Reduction Reactions

· Chemical Equations

· Net Ionic Equations

· Types of Oxidation-Reduction Reactions

· Acid-Base Reactions

· Precipitation Reactions

· Identifying Reaction Types: Summary

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Return toTable ofContents

Chemical Equations

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Chemical EquationsChemical equations are concise representations of

chemical reactions.

+ +⇒

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g)

-->

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The formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs.

Write the names of the products to the right of the arrow, also separated by plus signs.

Reactant + Reactant Product + Product

Chemical Equations

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Symbols used in chemical equations

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Skeleton equations

A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products.

Write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right.

Here is the equation for rusting:

Metallic Iron reacts with oxygen in the air to produce iron (III) oxide (rust).

Iron( metal) + Oxygen ( gas) ⇒ iron (III) oxide ( solid) (word equation)

Fe + O2 # Fe2O3 ( skeleton /chemical equation)

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Word Equations When ignited, methane gas reacts with oxygen gas

to produce carbon dioxide and steam.

CH4 gas O2 gas CO2 gas

+ +⇒

H2O gas

This "skeleton" equation is not balanced:

CH4 (g) + O2 (g) H2O (g) + CO2 (g)

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1 In the reaction CH4 (g) + O2 (g) # H2O (g) + CO2 (g) the products are:

A oxygen and water

B carbon dioxide and water

C oxygen and methane

D methane and carbon dioxide

E I don't know the answer to this.

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2 In the reaction CH4 (g) + O2 (g) # H2O (g) + CO2 (g) the products are:

A solids

B liquids

C gases

D dissolved in water (aqueous)

E cannot be determined

F I don't know how to answer this. answ

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Word equations to Chemical equations

Solid potasium chlorate decomposes in air to produce solid potassium chloride and oxygen gas.

The word equation is:

potasium chlorate (s) --> potassium chloride (s) + oxygen (g)

The unbalanced "skeleton" equation is:

KClO3(s) KCl(s) + O2(g)

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Write the word equation, then the skeleton equation Aluminum sulfate reacts with calcium chloride to produce calcium sulfate and aluminum chloride

Al2(SO4)3 + CaCl2 --> Ca(SO4) + AlCl3

Word equations to Chemical equations

Aluminum sulfate + calcium chloride --> calcium sulfate + aluminum chlorideSlide for Word equation

Slide for Skeleton equation

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Law of Conservation of Mass

“We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends.”

--Antoine Lavoisier, 1789

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Balancing Equations

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To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.

This is a balanced equation for making a bicycle. The numbers are called coefficients—small whole numbers that are placed in front of the formulas in an equation in order to balance it.

Balancing chemical equations

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CH4 (g) + 2 O2 (g) # CO2 (g) + 2 H2O (g)

Reactants appear on the left side of the equation.

Products appear on the right side of the equation.

The states of the reactants and products are written in parentheses to the right of each compound.


1C4H

4 O 1C2 O

2 O4H

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Coefficients are inserted to balance the equation.


CH4 (g) + 2 O2 (g) # CO2 (g) + 2 H2O (g)

1C4H

4 O 1C2 O

2 O4H

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Subscripts and Coefficients

Subscripts tell the number of atoms of each element in a molecule.

Coefficients tell the number of representative particles (atoms, molecules, or formula units).

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3 How many oxygen atoms are in one formula unit of calcium nitrate? (First, write the formula for calcium nitrate.)

A 2

B 3C 5

D 6

E I don't know how to answer this.

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4 How many nitrogen atoms are in one formula unit of ammonium sulfate?

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chlorine + sodium bromide # bromine + sodium chloride


Write a balanced chemical equation for this reaction.

First write a skeleton equation

Cl2 + NaBr # # Br2 + NaCl

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Then, count up the number of each type of element on each side of the reaction


Reactants ProductsCl: 2 Cl: 1

Na: 1 Na: 1

Br: 1 Br: 2

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Balancing chemical equationsNext, identify one element that is not balanced. It is best to start with an easy element. The fewer places an element appears on

both sides of a reaction, the easier it will be to balance.



Na: 1 Na: 1

Br: 1 Br: 2

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Identify the side that needs more of that particular element.



Na: 1 Na: 1

Br: 1 Br: 2

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Balancing chemical equationsDetermine which molecule or element will be getting the

coefficient. In this case, because we need more chlorine on the products side, we will have to add a coefficent to the NaCl, since

that is the only product containing chlorine.

Cl: 2

Na: 1

Br: 1



Na: 1 Na: 1

Br: 1 Br: 2

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To figure out what the coefficient should be, simply take the amount of that specific element you need from the molecule, and divide by the

amount of the element you have in the molecule.

Cl2 + NaBr # # Br2 + __NaCl2

NeedHave = 2

1 =

2

Cl: 2

Na: 1

Br: 1


Na: 1 Na: 1

Br: 1 Br: 2

If this is not a whole number, simply multiply ALL the substances in the reaction by some whole number to make the coefficients

whole numbers.

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Now, just reevaluate the amount of each element on the table

Cl: 2

Na: 1

Br: 1

Cl2 + NaBr # # Br2 + 2NaCl

Reactants ProductsCl: 2 Cl: 1 2

Na: 1 Na: 1 2

Br: 1 Br: 2

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Balancing chemical equationsContinue with these steps until all the elements are balanced.

When all the elements exist in equal amounts on both sides of the equation, you have a balanced chemical equation.

Cl: 2

Na: 1

Br: 1

Cl2 + 2NaBr # # Br2 + 2NaCl

Reactants ProductsCl: 2 Cl: 1 2

Na: 1 2 Na: 1 2

Br: 1 2 Br: 2

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Balancing chemical equationsSPECIAL NOTE: Make sure that when you are calculating your coefficents you are only looking at the amounts needed/had by

individual elements or molecules

Cl: 2

Na: 1

Br: 1

CH3OH + O2 # # CO2+ 2H2O

Reactants ProductsC: 1 C: 1

H: 4 H: 2 4

O: 1+2=3 O: 2+1=3 2+2=4

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Balancing chemical equationsSPECIAL NOTE: Here is the incorrect way to evaluate the

coefficent in this case

Cl: 2

Na: 1

Br: 1

CH3OH + O2 # # CO2+ 2H2O


H: 4 H: 2 4

O: 1+2=3 O: 2+1=3 2+2=4

NeedHave = 4

3 = WRONG!!!

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Balancing chemical equationsSPECIAL NOTE: Here is the correct way to evaluate

the coefficent in this case

Cl: 2

Na: 1

Br: 1

CH3OH + O2 # # CO2+ 2H2O


H: 4 H: 2 4

O: 1+2=3 O: 2+1=3 2+2=4

NeedHave = 4 - 1

2=

Because we already have 1 Oxygen from CH3OH, we only need 3 Oxygen from O2

Because O2 only has 2 Oxygen, the denominator must be 2.

32

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Balancing chemical equationsSPECIAL NOTE: Remember to make sure you get rid

of ALL fractions.

2CH3OH + 2x O2 # # 2CO2+ 2x2H2O32

Cl: 2

Na: 1

Br: 1

Reactants ProductsC: 1 2 C: 1 2

H: 4 8 H: 2 4 8

O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8

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Balancing chemical equationsIf you follow these steps, you'll be able to balance any

type of reaction.

2CH3OH + 3O2 # # 2CO2+ 4H2O

Cl: 2

Na: 1

Br: 1

Reactants ProductsC: 1 2 C: 1 2

H: 4 8 H: 2 4 8

O: 1+2=3 2+6=8 O: 2+1=3 2+2=4 4+4=8

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5 When the following equation is balanced, the coefficients are:

A 1, 1, 1 B 1, 2, 4

C 4, 1, 2

D 2, 2, 1

E 4, 1, 4

Na + O2 # Na2O

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6 When the following equation is balanced, the coefficients are

HgO # Hg + O2

A 1, 1, 1

B 1, 2, 4

C 4, 1, 2

D 2, 2, 1

E 4, 1, 4

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A 1, 1, 1, 1

B 4, 7, 4, 6

C 2, 3, 2, 3

D 1, 3, 1, 2 E 2, 3, 3, 2

Al + ZnCl2 # Zn + AlCl3

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A 1, 1, 1, 1

B 3, 2, 2, 3

C 2, 3, 2, 3

D 1, 3, 1, 2

E 2, 1, 2, 1

NaCl + CaI2 # NaI + CaCl2

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A 1, 1, 1, 1

B 4, 7, 4, 6

C 2, 3, 2, 3

D 1, 3, 1, 2 E 4, 3, 4, 3

NH3 + O2 # NO2 + H2O

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A 2, 3, 1, 6

B 2, 1, 3, 2

C 1, 1, 1, 1

D 4, 6, 3, 2

E 2, 3, 2, 3

Al(NO3)3 + Na2S # Al2S3 + NaNO3

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Reaction Types

Precipitation: formation of insoluble product out of aqueous solutions

Oxidation/Reduction: exchange of electrons between atoms/ions

Acid/Base: reaction between acids and bases

Most reactions can be classified as one of the following:

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Precipitation Reactions

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The giant clam's shell is made from the precipitation of CaCO3

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Precipitation reactions involve the reaction of water soluble ionic compounds to form a water insoluble product called a precipitate:

AgNO3(aq) + HCl(aq) --> AgCl(s) + HNO3(aq)

AgCl precipitate


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One must know which ionic compounds are water soluble and which are not. It is the insoluble ones that form precipitates!

Some general rules apply:

ALWAYS SOLUBLE

SOMETIMES SOLUBLE

INSOLUBLE

(unless paired with a soluble ion)


NH4+, C2H3O2-, ClO3-, Group 1 A metal ions, NO3-

Cl-,Br-, I- except when combined with Ag+, Hg+, and Pb2+

SO42- except when combined with Ag+, Hg+, Pb2+,

Ca2+, Sr2+, Ba2+

CO32-, PO4

3-, OH-, S2-, F-, O2-

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11 Which one of the following would be INSOLUBLE in water?

A Na2CO3

B NH4NO3

C AgNO3

D Mg(OH)2

E KCl

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12 Which of the following would be MOST SOLUBLE in water?

A CaSO4

B PbF2

C PbI2D Cu(OH)2

E CuSO4

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A solubility chart

provides more exact information

as to the individual

solubilities of various ionic substances.

Solubilities

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Solubility Chart

Note that S on this chart means that the compound is soluble. When you write a chemical equation, it will be (aq) aqueous.

Insoluble compounds are shown with the letter I. When you write a chemical equation, it will be (s) solid.

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Double Displacement Reactions

Precipitation reactions are often called "double replacement" or "double displacement" reactions because it appears as if the ions switch places with each other.

NaCl(aq) + AgNO3(aq) --> AgCl(s) + NaNO3(aq)

Na+ and Ag+ switch places

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Some examples of precipitation reactions....

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

AgNO3(aq) + KCl(aq) # AgCl(s) + KNO3(aq)

The formation of an insoluble precipitate is the driving force of these reactions

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A precipitation reaction will NOT occur if both products are water soluble....

2NaNO3(aq) + MgCl2(aq) --> 2NaCl(aq) + Mg(NO3)2(aq)

Since both products are soluble, no reaction occurs

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Predict the products of this reaction:

potassium phosphate + magnesium chloride -->

K3PO4 (aq) + MgCl2 (aq) --> KCl + Mg3(PO4)2


Now, put in the phases of the products and balance the equation.

Answer

2K3PO4 (aq) + 3MgCl2 (aq) --> 6KCl(aq) + Mg3(PO4)2(s)Answer

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Predict the products of this reaction:

calcium fluoride + sodium sulfate -->

CaF2 (aq) + Na2SO4 (aq) --> NaF + Ca(SO4)(s)


Now, put in the phases of the products and balance the equation.

CaF2 (aq) + Na2SO4 (aq) --> 2NaF (aq) + Ca(SO4)(s)

Answer

Answer

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13 Which of the following would be products from the reaction of aqueous Mg(C2H3O2)2 with aqueous Na3PO4?

A Mg3(PO4)2(aq) + NaC2H3O2(aq)B Mg3(PO4)2(s) + NaC2H3O2(aq)C Mg3(PO4)2(aq) + NaC2H3O2(s)D Mg3(PO4)2(s) + NaC2H3O2(s)E Mg3(PO4)2(s) + NaC2H3O2(s)

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14 One of the products of a reaction between silver nitrate and potassium carbonate will be:

A silver potassium(aq)

B potassium carbonate(aq)

C nitrate carbonate(aq)

D potassium nitrate(aq)

E potassium carbonate(s)

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Precipitation ReactionsIn order to better represent what is actually happening in a precipitation reaction, two things must be accounted for:

1. The ions that comprise a soluble ionic compound are separated when dissolved in water. For example....

NaCl(aq) + AgNO3(aq) --> AgCl(s) + NaNO3(aq)

can be written in ionic form as

Na+(aq) + Cl-(aq) + Ag+(aq) + NO3(aq)- --> AgCl(s) + Na+(aq) + NO3-(aq)

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In order to better represent what is actually happening in a precipitation reaction, two things must be accounted for:

2. Ions not involved in the reaction (not involved in the formation of the precipitate) are called spectator ions and can be eliminated. Reactions written this way are called Net Ionic Equations.

Ag+(aq) + Cl-(aq) --> AgCl(s)

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The complete ionic equation shows all aqueous substances (i.e. strong acids, strong bases, and soluble ionic compounds) dissociated into their ions.

For example:

NaCl (aq) would be written as Na+ (aq) + Cl- (aq)

Note: all ionic compound if soluble in water will readily dissociate into the corresponding (+) and (-) ions.


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Net Ionic Equations

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However, when all the aqueous species are dissociated into their respective ions, it becomes:

Ag+ (aq) + NO3- (aq) + K+ (aq) + Cl- (aq) --->AgCl (s) + K+ (aq) + NO3

- (aq)

Writing Net Ionic Equations

The equation between silver nitrate and potassium chloride would normally be shown as

AgNO3 (aq) + KCl(aq) --->AgCl (s) + KNO3 (aq)

This is called the complete ionic equation.

Note that the insoluble product does not dissociate.

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Spectator Ions

Ag (aq) + NO3-(aq) + K+(aq) + Cl-(aq) --->AgCl (s) + K+(aq) + NO3- (aq)

As this example shows, certain ions are present both before and after the reaction. Because they play no significant role in the reaction, they are known as "spectator ions."

A spectator ion is an ion that appears on both sides of an equation and is not directly involved in the reaction.

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The net ionic equation is an equation for a reaction in solution that shows only those particles that are directly involved in the chemical change.

To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right.

In other words, cancel out the spectator ions.


Ag (aq) + NO3-(aq) + K+(aq) + Cl-(aq) --->AgCl (s) + K+(aq) + NO3- (aq)

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After cancelling out the spectator ions, the only things left in the equation are those things that change, or react, during the course of the reaction.

Ag+(aq) + Cl-(aq) AgCl (s)


Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3

-(aq)

This is called the net ionic equation.

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Write a balanced molecular equation.

Steps for Net Ionic Equations

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Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate.


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Cross out anything that remains unchanged from the left side to the right side of the equation.


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Write the net ionic equation with the species that remain.


In all cases (involving double replacement), it will be the reaction between the ions that produces the insoluble precipitate.

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Write a balanced molecular equation. Pb(NO3)2 (aq)+ 2 KI (aq) --> PbI2 (s)+ 2 KNO3 (aq)

Dissociate any reactants or products that are aqueous. Pb2+

(aq) + 2NO3-(aq)+ 2K+

(aq)+ 2I-(aq)# PbI2 (s)+ 2K+

(aq)+ 2NO3-(aq)


Pb2+(aq) + 2NO3

-(aq)+ 2K+

(aq)+ 2I-(aq)# PbI2 (s)+ 2K+

(aq)+ 2NO3-(aq)

Write the net ionic equation with the species that remain. Pb2+

(aq) + 2 I-(aq) --> PbI2 (s)

Example Net Ionic Equation

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Practice writing the balanced equation, complete ionic equation and net ionic equation for these reactions.

1. calcium nitrate (aq) and potassium carbonate (aq) --->

Ca2+ (aq) + CO32- (aq) --> CaCO3 (s)


Slide for Answer

[*]

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Practice writing the balanced equation, complete ionic equation and net ionic equation for these reactions.

2. silver nitrate (aq) and sodium phosphate (aq) -->

3Ag+ (aq) + PO43- (aq) --> Ag3PO4 (s)

Writing Net Ionic Equations [*]

Slide for Answer

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15 Which of the following would be a correct net-ionic equation between aqueous BaCl2 and aqueous NaOH?

ANa+(aq) + OH-(aq) + Ba2+(aq) + Cl-(aq) -->NaBa(s) + ClOH(aq)

B Ba2+(aq) + 2Cl-(aq) --> BaCl2(s)

C Ba2+(aq) + 2OH-(aq) --> Ba(OH)2(s)

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

ENa+(aq) + OH-(aq) + Ba2+(aq) + 2Cl-(aq) -->Ba(OH)2(s) + NaCl(aq)

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16 Which of the following aqueous solutions could be used to form a precipitate with MgSO4?

A NaClB NH4NO3

C BaI2

D KC2H3O2

E LiClO3

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17 Which of the following would be spectator ions when aqueous lead(II)nitrate and sodium iodide are mixed?

A Pb2+ and I-B NO3- and Na+C NO3- and I-D Pb2+ and Na+E Na+ and I-

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Real World Application

This is a river in China that became contaminated with Cd2+ ions.

Knowing what you know about precipitation reactions, what do you think could be added to remove the Cd2+ ions?

Cd ions are often removed by adding hydroxides or sulfides to form precipitates that can be filtered out of the watermove for answer

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Oxidation-Reduction Reactions

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Oxidation/Reduction Reactions

The thermite reaction between iron(III)oxide and Al generates a lot of heat!

Recall that Oxidation/Reduction Reactions involve exchange of electrons between atoms/ions

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These reactions, often called REDOX reactions, involve a transfer of electrons from one element to another.

4Al(s) + 3O2(g) 2Al2O3

Charge 0 0 +3 -2

Each Al loses 3 electrons Each O gains 2 electrons

Oxidation

element loses electronsReduction

element gains electrons

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The electrons lost/gained must be balanced in a REDOX reaction


Each Al loses 3 electrons Each O gains 2 electrons

4Al(s) + 3O2(g) --> 2Al2O3

4 x Al x 3e- lost = 12 e- lost 6 x O x 2e- gained = 12 e- gained

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Determining Oxidation StatesIn order to determine if a reaction is an oxidation/reduction reaction and which element got oxidized or reduced, one must be able to track the charges (oxidation states) of elements throughout the reaction.

Zn + 2H+ --> Zn2+ + H2

0 +1 +2 0Oxidation States

Since the charges on both the zinc and hydrogen change, this is definitely a redox reaction.

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Determining Oxidation States

Substance Oxidation State

H2(g) 0

Ca(s) 0

Na+(aq) +1

F-(aq) -1

All elements in their standard (neutral) state, have an oxidation state of zero. If the element has a charge listed, this is it's

oxidation state.

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Rule 1: The charges of all the elements in the compound have to add up to the charge of the compound.

Example: ZnO The compound is neutral so...

Charge of Zn + Charge of O = 0

Example: NO3- The compound has a charge of -1 so...

Charge of N + charge of O = -1

Determining Oxidation StatesIf the element is combined with others, the oxidation state will have to be deduced using the periodic table, your knowledge of ionic compounds, and some mathematics. Here are some general guidelines...

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Guideline 1: The charges of all the elements in the compound have to add up to the charge of the compound.

Guideline 2: Using your periodic table, find the charge on the anion and use this and what you know to be the charge on the whole compound to find the charge on the cation. Typically, the cation is written first and the anion second.

Example: ZnO Charges

zinc oxide ZnO

? 2- 0

2+ + 2- = 0

zinc has a +2 oxidation state!


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Another Example: NO3- Charges

N Ox3 NO3-

? -2(3) = -6 -1

+5 + -6 = -1

Oxidation States: N = +5 O = -2


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Another Example: Cr2O72-(aq)

Charges

Cr x 2 O x 7 Cr2O72-

? -2(7) =-14 -2

+12 + -14 = -2

Since Cr x 2 = +12 ... the oxidation state of each Cr must be +6!

Oxidation states: Cr = +6 O = -2


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Another example: HS-

Charges

H S HS-

? -2 -1

+1 + -2 = -1

H = +1, S = -2

Move for answer


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Another Example: N2O4

Charges

Nx2 Ox4 N2O4

? -2(4) = -8 0

+8 + -8 = 0

Since Nx2 =8, each N = 4

so.... N = +4, O = -2


Move for answer

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18 In which of the following substances would zinc have an oxidation state of 0?

A ZnSB ZnC Zn2+

D ZnSO4

E ZnCl2

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19 What is the oxidation state of P in the phosphate ion -- PO43-?

A 0B +1C +3D +5E -3

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20 What is the oxidation state of Cl in ClO2-?

A 0B -1C +1D +3E +5

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For elements containing three elements, find the oxidation states of the first and last from the periodic table and then find the middle element (usually but not always a transition metal).

Example: Na2S2O3

Charges

Na x2 Sx2 Ox3 Na2S2O3

+1(2)= +2 ? -2(3) = -6 0

2 + 4 -6 0


Since Sx2 = 4, each sulfur will have a charge of just +2

so....Na =+1, S =+2, and O = -2

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Example: Mg(OH)2

charges

Mg Ox2 Hx2 Mg(OH)2

+2 -2(2)=-4 +1(2)=+2 0

2 + -4 + 2 = 0

All of these charges could be obtained using the periodic table so nothing needed to be figured out!

Mg = +2, O = -2, and H = +1


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Example: KMnO4

charges

K Mn Ox4 KMnO4

+1 ? -2(4)=-8 0

1 + 7 -8 = 0

So... K = +1, Mn = +7, and O = -2

move for answer


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21 What is the oxidation state of each element in K2TeO4?

A K = +1, Te = +6, O = -2B K = +2, Te = +4, O = -2C K = +1, Te = +4, O = -2D K = +1, Te = +2, O = -2E K = +1, Te = +8, O = -2

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22 In which of the following substances would S have an oxidation state of +4?

A Na2SO4

B Na2SO3

C Na2SD S8

E SO3

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Exceptions with Determining Oxidation States

1)Peroxides like Na2O2 and H2O2

Oxygen has an oxidation state of -1 instead of -2

2) Ammonia (NH3) and ammonium (NH4+)

Usually the element with the - charge is written second but that is not the case here. N carries a -3 charge in both instances and H carries a +1 charge.

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23 In which of the following would oxygen have an oxidation state of -1?

A O2

B Na2OC Li2O2

D H2OE None of these an

swer

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Find the Oxidation States

What are the oxidation states of each element in the following reaction?

Fe2+(aq) + MnO4-(aq) + H+ --> H2O + Mn2+ + Fe3+

+2 +7, -2 +1 --> +1, -2 +2 +3slide for answer

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What are the oxidation states of each of the elements in the reaction?

2H2O2 --> 2H2O + O2

+1, -1 +1,-2 0

*note that H2O2 is a peroxide

Key: Ignore coefficients when you find oxidation states!

Find the Oxidation States

slide for answer

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24 In the following equation: 2KClO3 --> 2KCl + 3O2

the oxidation state of O changes from:

A -2 --> -2B -6 --> -2C -6 --> 0D -2 --> 0E -1 --> 0

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25 In the following equation: 2KClO3 --> 2KCl + 3O2

the oxidation state of Cl changes from:A -1 --> -1B 0 --> -1C +3 --> +5D + 5 --> -1E +5 --> 0

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Which species got oxidized/reduced?

To determine which species in a reaction got oxidized or reduced, one must know what it means to be oxidized and reduced.Oxidation = Loss of electrons

Na --> Na+ + e-

0 --> +1

Notice that an element becomes more + when it gets oxidized.

Reduction = Gain of electrons

Mg2+ + 2e - --> Mg

+2 --> 0

Notice that an element becomes less + when it gets reduced.

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Which element got oxidized and which got reduced in the following reaction?

2KClO3 --> 2KCl + 3O2

Find Ox. States +1,+5, -2 +1,-1 0

Oxygen went from -2 --> 0 becoming more + so it

must have lost electrons

Chlorine went from +5 --> -1 becoming less + so it must

have gained electrons

reduced oxidized

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Which of the following elements got oxidized and reduced in the following reaction?

2F-(aq) + Cl2(g) --> 2Cl-(aq) + F2(g)

-1 0 -1 0

Flourine went from -1 to 0 becoming more + meaning electrons were lost = oxidation!

Chlorine went from 0 to -1 becoming more - meaning electrons were gained = reduction!

move for answer

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Anti-oxidants like carotenoids found in veggies have many electrons to lose so they help reduced the radicals so the molecules in your body don't get harmed!!! So...eat your veggies!!!

[ ]2-

carotenoid ----->

free radical singlet O ----->

An oxidant is a chemical species that wants to be reduced so it causes something else to get oxidized. Free radical species like singlet oxygen are oxidants and not good for you as they will get electrons from molecules in your body that need them!

O + 2e- --> O

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26 Which of the following represents a reduction?

A An elements charge going from -3 --> -2B An elements charge going from -2 -->-3C An elements charge going from 0 --> +2D An elements charge going from +1 --> +3E None of these

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27 Which of the following represents an oxidation?

A Al3+(aq) --> Al(s)B F2(g) --> 2F-(aq) C Mn7+ --> Mn2+

D Fe2+(aq) --> Fe3+(aq)E O-(aq) --> O2-(aq) an

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28 In which of the following equations does O get oxidized?

A 2H2O2 -- 2H2O + O2

B 2H2O --> 2H2 + O2

C CH4 + 2O2 --> CO2 + 2H2OD 3Fe + 3O2 --> 2Fe2O3

E None of these answ

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29 Which of the following is NOT an oxidation/reduction reaction?

A Ca + 2H+ --> Ca2+ + H2

B H2 + Cl2 -->2HClC 4Al + 3O2 --> 2Al2O3

D CaO + CO2 --> CaCO3

E Mg3N2 --> 3Mg + N2

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Chromium metal is used as rust resistant coating over steel as shown on the motorcycle. This is accomplished by reducing chromium ions.

C gets oxidized and releases a lot of energy which is used to generate the potential so electrons will move through the wire and reduce the Cr3+ ions. CH4 + 2O2 --> CO2 + 2H2O

-4 +4


What element do you think gets oxidized at the natural gas burning power plant to provide the energy so chromium can get reduced?

Cr3+ + 3e- --> Cr(s)

Slide for Answer

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Types of Oxidation-Reduction Reactions

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Types of Oxidation/Reduction Reactions

There are essentially four types of Redox reactions:1. Synthesis or Combination - two or more substances combine

2Mg(s) + O2(g) --> 2MgO(s)

2. Decomposition - a substance breaks into two or more compounds

2LiClO3(s) --> 2LiCl(s) + 3O2(g)

3. Combustion - a substance reacts with oxygen.

C(s) + O2(g) --> CO2(g)

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g)

4. Disproportionation - the same material gets both oxidized and reduced

Hg2Cl2 → Hg + HgCl2

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Combination/Synthesis Reactions

Examples:

· 2 Mg (s) + O2 (g) 2 MgO (s)· N2 (g) + 3 H2 (g) 2 NH3 (g)· C3H6 (g) + Br2 (l) C3H6Br2 (l)

Two or more substances react to form one product.

Mg O2 MgO

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30 Which of the following is a combination reaction?

A H2O --> H2 +O2

B Na + Cl2 --> NaCl

C AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2

D C3H8 + O2 --> H2O + CO2

E CaCO3 --> CaO + CO2

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One substance breaks down into two or more substances.

Decomposition Reactions

Examples:

CaCO3 (s) CaO (s) + CO2 (g)

2 KClO3 (s) # 2 KCl (s) + 3 O2 (g)

2 NaN3 (s) 2 Na (s) + 3 N2 (g)

# +

2 H2O # O2 + 2 H2

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31 Which of the following is a decomposition reaction?

A H2O --> H2 +O2

B Na + Cl2 --> NaCl


D C3H8 + O2 --> H2O + CO2

E Ca2+(aq) + SO42-(aq) --> CaSO(s)

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Combustion Reactions

Examples:CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)

C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)

These are generally rapid reactions that produce a flame.

Most often involve hydrocarbons reacting with oxygen in the air.

O2 is always one of the reactants.

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Note: substances other than hydrocarbons may also undergo combustion:

Mg (s) + O2 (g) ---> MgO (s)N2 (g) + 2 O2 (g) ---> 2 NO2 (g)

These last two may also be classified as combination reactions.

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32 Which of the following is a combustion reaction?

A H2O --> H2 +O2

B Na + Cl2 --> NaCl


D C3H8 + O2 --> H2O + CO2

E Ca2+ + SO42- --> CaSO4(s)

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Combustion reactions are easily identified by oxygen as a reactant. However, the products of a combustion reaction may vary depending on how much oxygen is available.

Complete combustion

products are carbon dioxide and water

Incomplete combustion

products are carbon monoxide and water

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Disproportionation ReactionsThe same element gets both oxidized and reduced.

Hg2Cl2 --> 2Hg + HgCl2

Oxid. States: +1 , -1 0 +2 , -1

Hg gets both oxidized (+1 -->+2) and reduced (+1 -->0)

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Disproportionation Reactions

Is the following a disproportionation reaction and if so, what element is getting both oxidized and reduced?

Cl2 + 6 OH− → 5 Cl− + ClO3− + 3 H2O

Oxid.States 0 -1,+1 -1 +5,-2 +1,-2

It is! Cl is the element that gets both oxidized and reducedmove for answer

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33 Which of the following would be a disproportionation reaction?

A CO → C + CO2

B CaCO3 --> CaO + CO2

C H2O --> H2 + O2

D H2 + F2 --> 2HFE none of these

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34 Which element gets both oxidized and reduced in the following disproportionation reaction?

NaOH + Cl2 --> NaCl + NaClO + H2OA NaB ClC OD HE This is NOT a disproportionation reaction

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Acid-Base Reactions

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Acid/Base Reactions

Soda pop contains two common weak acids:

phosphoric acid (H3PO4) and carbonic acid (H2CO3)

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Acid = H+ ion donor Base = H+ acceptor

H+ acceptor H+ donor

Bronsted-Lowry Definition of Acids and Bases

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Acid = electron pair acceptor Base = electron pair donor

** unless otherwise noted, we will be using the bronsted/lowry definition of acids and bases throughout the rest of the presentation.

Lewis Definition of Acids and Bases

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Acid/Base Reactions

Bronsted/Lowry Acid/Base reactions involve the transfer of H+ ions from one an acid (H+ donor) to a base (H+ acceptor)

Example: HC2H3O2(aq) + CO32-(aq) --> HCO3-(aq) + C2H3O2-(aq)

HC2H3O2(aq) gave away it's H+ = acid

CO32-(aq) accepted an H+ = base

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Acid/Base Reactions

Identify the acid and base in the following reaction:

CN- + H2O --> HCN + OH-

CN- accepted an H+ so it is a base

H2O donated an H+ so it is an acid

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Identify the acid and base in the following reaction:

HCO3- + HF --> F- + H2CO3

HCO3- accepted an H+ so it was a base

HF donated an H+ so it was an acid

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Acid/Base Reactions

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Neutralization reactions are a special type of acid/base reaction in which an acid and base react to produce water.

Example: HF + OH- --> H2O + F-

Neutralization Reactions

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35 Which of the following acid/base reactions represent a neutralization reaction?

A H+ + CN- --> HCNB HNO2 + OH- --> H2O + NO2-C HCN + NH3 --> NH4+ + CN-D HCO3- + H2O --> CO3

2- + H3O+E none of these

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The classic childhood reaction of vinegar (HC2H3O2) and baking soda (HCO3-) is an acid/base

reaction.

Which molecule is the conjugate base of acetic acid (HC2H3O2)?

C2H3O2-answer


HC2H3O2(aq) + HCO3-(aq) --> C2H3O2-(aq) + CO2(g) + H2O(l)

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Identifying Reaction Types

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Identifying what kind of reaction it is?

One can determine the type of chemical reaction by following some basic guidelines....

1) Are you forming a precipitate?

Look for the formation of an insoluble solid

2) Check to see if H+ ions are being transferred?

If so, you've got an acid/base reaction

3) Check oxidation states

If they change, you've got an oxidation/reduction reaction

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What kind of reaction is the following?

C4H8(s) + O2(g) --> CO2(g) + H2O(g)

1) Is there a precipitate?

2) Is there a transfer of H+ ions?

3) Check oxidation states....

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What kind of reaction is the following?

C4H8(s) + O2(g) --> CO2(g) + H2O(g)

1) Is there a precipitate? No - So... not a precipitation reaction

2) Is there a transfer of H+ ions? No - So...not an acid/base reaction

3) Check oxidation states....

C4H8(s) + O2(g) --> CO2(g) + H2O(g)

-2,+1 0 +4,-2 +1,-2

Carbon changes from -2 --> +4 and Oxygen changes from 0 -->-2. Oxidation states are definitely changing = REDOX!!!

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36 Which of the following would be an example of an oxidation/reduction reaction?

A CH3COOH + NH3 --> NH4+ + CH3COO-B AlCl3(s) --> Al3+(aq) + 3Cl-(aq)C 2Ag+(aq) + Cu(s) --> Cu2+(aq) + 2Ag(s)D H+(aq) + OH-(aq) --> H2O(l)E Zn2+(aq) + CO3

2-(aq) --> ZnCO3(s)

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What type of chemical reaction is the following?

Mg2+(aq) + 2OH-(aq) --> Mg(OH)2(s)

1. Are you forming a precipitate? Yes .... Precipitationmove for answer


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37 Which of the following is NOT an acid/base reaction?

A H2O + CN- --> OH- + HCNB 2CuO -->2Cu + O2

C NH3 + HSO4- --> NH4+ + SO42-

D H+ + OH- --> H2OE All of these are acid/base reactions

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