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Chemical Reactions

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Slide 3 / 142 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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Chemical Equations

Slide 5 / 142 Chemical Equations

Chemical equations are concise representations of chemical reactions.

+ +

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

• ->

Slide 6 / 142

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

Slide 7 / 142 Symbols used in chemical equations Slide 8 / 142 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)

Slide 9 / 142 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)

Slide 10 / 142

1 In the reaction CH4 (g) + O2 (g)  H2O (g) + CO2 (g)

the products are: A

• xygen and water

B carbon dioxide and water

C

• xygen and methane

D methane and carbon dioxide E I don't know the answer to this.

answer

Slide 11 / 142

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.

answer

Slide 12 / 142 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)

Slide 13 / 142

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 chloride

Slide for Word equation

Slide for Skeleton equation

Slide 14 / 142 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
• beys 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 Slide 17 / 142

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.

Balancing chemical equations

1C 4H 4 O 1C 2 O 2 O 4H

Slide 18 / 142

Coefficients are inserted to balance the equation.

Balancing chemical equations

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

1C 4H 4 O 1C 2 O 2 O 4H

Slide 19 / 142 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).

Slide 20 / 142

3 How many oxygen atoms are in one formula

unit of calcium nitrate? (First, write the formula

for calcium nitrate.)

A

2

B

3

C

5

D

6

E

I don't know how to answer this.

answer

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4 How many nitrogen atoms are in one formula

unit of ammonium sulfate?

answer

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2 2 1 1 2 2 2 2

H2 + Cl2  HCl H2 + Cl2  2HCl

Balancing chemical equations

unbalanced balanced

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chlorine + sodium bromide  bromine + sodium chloride

Balancing chemical equations

Write a balanced chemical equation for this reaction. First write a skeleton equation Cl2 + NaBr Br2 + NaCl

Slide 24 / 142 Balancing chemical equations

Then, count up the number of each type of element on each side of the reaction Cl2 + NaBr Br2 + NaCl

Reactants Products

Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2

Slide 25 / 142 Balancing chemical equations

Next, 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. Cl2 + NaBr Br2 + NaCl

Reactants Products

Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2

Slide 26 / 142 Balancing chemical equations

Identify the side that needs more of that particular element. Cl2 + NaBr Br2 + NaCl

Reactants Products

Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2

Slide 27 / 142 Balancing chemical equations

Determine 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

Cl2 + NaBr Br2 + NaCl

Reactants Products

Cl: 2 Cl: 1 Na: 1 Na: 1 Br: 1 Br: 2

Slide 28 / 142 Balancing chemical equations

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 + __NaCl

2

Need Have = 2 1 =

2

Cl: 2 Na: 1 Br: 1

Reactants Products

Cl: 2 Cl: 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.

Slide 29 / 142 Balancing chemical equations

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

Cl: 2 Na: 1 Br: 1

Cl2 + NaBr Br2 + 2NaCl

Reactants Products

Cl: 2 Cl: 1 2 Na: 1 Na: 1 2 Br: 1 Br: 2

Slide 30 / 142 Balancing chemical equations

Continue 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 Products

Cl: 2 Cl: 1 2 Na: 1 2 Na: 1 2 Br: 1 2 Br: 2

Slide 31 / 142 Balancing chemical equations

SPECIAL 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 Products

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

Slide 32 / 142 Balancing chemical equations

SPECIAL NOTE: Here is the incorrect way to evaluate the coefficent in this case

Cl: 2 Na: 1 Br: 1

CH3OH + O2 CO2+ 2H2O

Reactants Products

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

Need Have = 4 3 = WRONG!!!

Slide 33 / 142 Balancing chemical equations

SPECIAL NOTE: Here is the correct way to evaluate the coefficent in this case

Cl: 2 Na: 1 Br: 1

CH3OH + O2 CO2+ 2H2O

Reactants Products

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

Need Have = 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.

3 2

Slide 34 / 142 Balancing chemical equations

SPECIAL NOTE: Remember to make sure you get rid

• f ALL fractions.

2CH3OH + 2x O2 2CO2+ 2x2H2O

3 2

Cl: 2 Na: 1 Br: 1

Reactants Products

C: 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

Slide 35 / 142 Balancing chemical equations

If 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 Products

C: 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

answer

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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

answer

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7 When the following equation is balanced, the

coefficients are

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

answer

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8 When the following equation is balanced, the

coefficients are

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

answer

Slide 40 / 142

9 When the following equation is balanced, the

coefficients are

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

answer

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10 When the following equation is balanced, the

coefficients are

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

answer

Slide 42 / 142 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

Slide 44 / 142 Precipitation Reactions

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

Slide 45 / 142

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

Precipitation Reactions Slide 46 / 142

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)

Precipitation Reactions

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-, PO43-, 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

answer

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12 Which of the following would be MOST SOLUBLE in

water?

A CaSO4 B PbF2 C PbI2 D Cu(OH)2 E CuSO4

answer

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A solubility chart provides more exact information as to the individual solubilities of various ionic substances.

Solubilities Slide 50 / 142 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.

Slide 51 / 142 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

Slide 52 / 142 Precipitation Reactions

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

Slide 53 / 142 Precipitation Reactions

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

Precipitation Reactions

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)

Precipitation Reactions

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

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

Answer Answer Slide 56 / 142

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)

answer

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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)

answer

Slide 58 / 142 Precipitation Reactions

In 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)

Slide 59 / 142 Precipitation Reactions

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)

Slide 60 / 142

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.

Precipitation Reactions

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Net Ionic Equations

Slide 62 / 142

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.

Slide 63 / 142 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.

Writing Net Ionic Equations

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

Slide 65 / 142

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) Writing Net Ionic Equations

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) This is called the net ionic equation.

Slide 66 / 142

Write a balanced molecular equation.

Steps for Net Ionic Equations

Slide 67 / 142

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

Steps for Net Ionic Equations Slide 68 / 142

Write a balanced molecular equation. Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate. Cross out anything that remains unchanged from the left side to the right side of the equation.

Steps for Net Ionic Equations Slide 69 / 142

Write a balanced molecular equation. Dissociate any reactants or products that are aqueous. All solids, liquids, and gases stay intact and do not dissociate. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain.

Steps for Net Ionic Equations

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

Slide 70 / 142

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) Cross out anything that remains unchanged from the left side to the right side of the equation. 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 Slide 71 / 142

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)

Writing Net Ionic Equations

Slide for Answer

[*] Slide 72 / 142

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?

A

Na+(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) E

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

answer

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16 Which of the following aqueous solutions could be

used to form a precipitate with MgSO4?

A NaCl B NH4NO3 C BaI2 D KC2H3O2 E LiClO3

answer

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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-

answer

Slide 76 / 142 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 water

move for answer Slide 77 / 142

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Oxidation-Reduction Reactions

Slide 78 / 142 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

Slide 79 / 142 Oxidation/Reduction Reactions

These reactions, often called REDOX reactions, involve a transfer of electrons from one element to another. 4Al(s) + 3O2(g) 2Al2O3

Charge +3 -2

Each Al loses 3 electrons Each O gains 2 electrons

Oxidation element loses electrons Reduction element gains electrons

Slide 80 / 142

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

Oxidation/Reduction Reactions

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

Slide 81 / 142 Determining Oxidation States

In 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 0

Oxidation States

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

Slide 82 / 142 Determining Oxidation States

Substance Oxidation State H2(g) Ca(s) 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

• xidation state.

Slide 83 / 142

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 States

If 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...

Slide 84 / 142

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

• xide

ZnO ? 2- 2+ + 2- = zinc has a +2 oxidation state!

Determining Oxidation States

Slide 85 / 142

Another Example: NO3- Charges N Ox3 NO3- ?

• 2(3) = -6
• 1

+5 +

• 6

= -1 Oxidation States: N = +5 O = -2

Determining Oxidation States Slide 86 / 142

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

Determining Oxidation States Slide 87 / 142

Another example: HS- Charges H S HS- ?

• 2
• 1

+1 +

• 2 = -1

H = +1, S = -2

Move for answer

Determining Oxidation States Slide 88 / 142

Another Example: N2O4 Charges Nx2 Ox4 N2O4 ?

• 2(4) = -8

+8 +

• 8

= Since Nx2 =8, each N = 4 so.... N = +4, O = -2

Determining Oxidation States

Move for answer

Slide 89 / 142

18 In which of the following substances would zinc have an

• xidation state of 0?

A ZnS B Zn C Zn2+ D ZnSO4 E ZnCl2

answer

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

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

answer

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

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

answer

Slide 92 / 142

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

2 + 4

• 6

Determining Oxidation States

Since Sx2 = 4, each sulfur will have a charge of just +2 so....Na =+1, S =+2, and O = -2

Slide 93 / 142

Example: Mg(OH)2 charges Mg Ox2 Hx2 Mg(OH)2 +2

• 2(2)=-4

+1(2)=+2 2 +

• 4

+ 2 = 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

Determining Oxidation States Slide 94 / 142

Example: KMnO4 charges K Mn Ox4 KMnO4 +1 ?

• 2(4)=-8

1 + 7

• 8

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

move for answer Determining Oxidation States Slide 95 / 142

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

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

answer

Slide 96 / 142

22 In which of the following substances would S have an

• xidation state of +4?

A Na2SO4 B Na2SO3 C Na2S D S8 E SO3

answer

Slide 97 / 142 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.

Slide 98 / 142

23 In which of the following would oxygen have an oxidation

state of -1?

A O2 B Na2O C Li2O2 D H2O E None of these

answer

Slide 99 / 142 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 +3 slide for answer

Slide 100 / 142

What are the oxidation states of each of the elements in the reaction? 2H2O2 --> 2H2O + O2 +1, -1 +1,-2 *note that H2O2 is a peroxide

Key: Ignore coefficients when you find oxidation states!

Find the Oxidation States

slide for answer

Slide 101 / 142

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

the oxidation state of O changes from:

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

answer

Slide 102 / 142

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

the oxidation state of Cl changes from:

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

answer

Slide 103 / 142 Which species got oxidized/reduced?

To determine which species in a reaction got oxidized or reduced,

• ne 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.

Slide 104 / 142 Which species got oxidized/reduced?

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

• xidized

Slide 105 / 142 Which species got oxidized/reduced?

Which of the following elements got oxidized and reduced in the following reaction? 2F-(aq) + Cl2(g) --> 2Cl-(aq) + F2(g)

• 1
• 1

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 Slide 106 / 142 Real World Application

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

Slide 107 / 142

26 Which of the following represents a reduction?

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

answer

Slide 108 / 142

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)

answer

Slide 109 / 142

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

A 2H2O2 -- 2H2O + O2 B 2H2O --> 2H2 + O2 C CH4 + 2O2 --> CO2 + 2H2O D 3Fe + 3O2 --> 2Fe2O3 E None of these

answer

Slide 110 / 142

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

A Ca + 2H+ --> Ca2+ + H2 B H2 + Cl2 -->2HCl C 4Al + 3O2 --> 2Al2O3 D CaO + CO2 --> CaCO3 E Mg3N2 --> 3Mg + N2

answer

Slide 111 / 142

Chromium metal is used as rust resistant coating over steel as shown

• n 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

Real World Application

What element do you think gets

• xidized at the natural gas

burning power plant to provide the energy so chromium can get reduced? Cr3+ + 3e- --> Cr(s) Slide for Answer

Slide 112 / 142

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Types of Oxidation-Reduction Reactions

Slide 113 / 142 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

Slide 114 / 142 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

• ne product.

Mg O2 MgO

Slide 115 / 142

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

answer

Slide 116 / 142

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

Slide 117 / 142

31

Which of the following is a decomposition reaction?

A H2O --> H2 +O2

B Na + Cl2 --> NaCl C AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2 D C3H8 + O2 --> H2O + CO2 E Ca2+(aq) + SO4 2-(aq) --> CaSO(s)

answer

Slide 118 / 142 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.

Slide 119 / 142 Combustion Reactions

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.

Slide 120 / 142

32

Which of the following is a combustion reaction?

A H2O --> H2 +O2

B Na + Cl2 --> NaCl

C AgNO3 + BaSO4 --> Ag2SO4 + Ba(NO3)2 D C3H8 + O2 --> H2O + CO2 E Ca2+ + SO42- --> CaSO4(s)

answer

Slide 121 / 142 Combustion Reactions

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

• n how much oxygen is available.

Complete combustion products are carbon dioxide and water Incomplete combustion products are carbon monoxide and water

Slide 122 / 142 Disproportionation Reactions

The same element gets both oxidized and reduced. Hg2Cl2

• -> 2Hg

+ HgCl2

• Oxid. States: +1 , -1

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

Slide 123 / 142 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 reduced

move for answer

Slide 124 / 142

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 --> 2HF E none of these

answer

Slide 125 / 142

34 Which element gets both oxidized and reduced in the

following disproportionation reaction? NaOH + Cl2 --> NaCl + NaClO + H2O

A Na B Cl C O D H E This is NOT a disproportionation reaction

answer

Slide 126 / 142

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Acid-Base Reactions

Slide 127 / 142 Acid/Base Reactions

Soda pop contains two common weak acids: phosphoric acid (H3PO4) and carbonic acid (H2CO3)

Slide 128 / 142

Acid = H+ ion donor Base = H+ acceptor H+ acceptor H+ donor

Bronsted-Lowry Definition of Acids and Bases Slide 129 / 142

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 Slide 130 / 142 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

Slide 131 / 142 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

Slide 132 / 142

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

move for answer

Acid/Base Reactions

Slide 133 / 142

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 Slide 134 / 142

35 Which of the following acid/base reactions represent a

neutralization reaction?

A H+ + CN- --> HCN B HNO2 + OH- --> H2O + NO2- C HCN + NH3 --> NH4+ + CN- D HCO3- + H2O --> CO32- + H3O+ E none of these

answer

Slide 135 / 142

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

Real World Application

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

Slide 136 / 142

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Identifying Reaction Types

Slide 137 / 142 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

Slide 138 / 142 Identifying what kind of reaction it is?

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....

Slide 139 / 142 Identifying what kind of reaction it is?

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

+4,-2 +1,-2 Carbon changes from -2 --> +4 and Oxygen changes from 0 -->-2. Oxidation states are definitely changing = REDOX!!!

Slide 140 / 142

36 Which of the following would be an example of an

• xidation/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) + CO32-(aq) --> ZnCO3(s)

answer

Slide 141 / 142

What type of chemical reaction is the following? Mg2+(aq) + 2OH-(aq) --> Mg(OH)2(s)

• 1. Are you forming a precipitate? Yes .... Precipitation

move for answer

Identifying what kind of reaction it is? Slide 142 / 142

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

A H2O + CN- --> OH- + HCN B 2CuO -->2Cu + O2 C NH3 + HSO4- --> NH4+ + SO42- D H+ + OH- --> H2O E All of these are acid/base reactions

answer