Hewitt/Suchocki/Hewitt Conceptual Physical Science …€¦ · PPT file · Web view ·...

Conceptual PhysicalScience5th Edition

Chapter 18: TWO CLASSES OF

CHEMICAL REACTIONS

This lecture will help you understand:

• Acids Donate Protons, Bases Accept Them• Relative Strengths of Acids and Bases• Acidic, Basic, and Neutral Solutions• Acidic Rain and Basic Oceans• Losing and Gaining Electrons• Harnessing the Energy of Flowing Electrons• Electrolysis• Corrosion and Combustion

Acids Donate Protons, Bases Accept Them

Acid• A chemical that donates a hydrogen ion, H+

Base• A chemical that accepts a hydrogen ion, H+

The hydrogen atom

The hydrogen ion

proton

Accepts

Donates

H2OHCl +

H3O+Cl– +

H3O+Cl–H2OHCl + +

H3O+Cl–H2OHCl + +donor

acceptor

H3O+Cl–H2OHCl + +

(acid) (base)

H2O NH3+

NH4+OH– +

H2O NH3+

NH4+OH– +

NH4+OH–H2O NH3+ +

acceptor

NH4+OH–H2O NH3+ +

(acid) (base)

NH4+OH–H2O NH3+ +

NH4+OH–H2O NH3+

(acid) (base) +

NH4+OH–H2O NH3+ +

(acid) (base) (acid) (base)

When water behaves as an acid, what does it lose?

A. A hydrogen ion.B. A hydrogen atom. C. An electron.D. Water can’t behave as an acid.

Acids Donate Protons, Bases Accept ThemCHECK YOUR NEIGHBOR

When water behaves as an acid, what does it lose?

Acids Donate Protons, Bases Accept ThemCHECK YOUR ANSWER

When water behaves as a base, what does it gain?

Which water molecule is behaving as an acid, and which is behaving as a base?

A. Molecule B as a base; Molecule A as an acid.B. Molecule B as an acid; Molecule A as a base.C. Both Molecules A and B are behaving as acids.D. Both Molecules A and B are behaving as bases.

Molecule A Molecule B

Molecule A

Salt: An ionic compound formed from the reaction of an acid and a base.

What salt forms from the reaction of hydrogen chloride, HCl, with potassium hydroxide, KOH?

A. KClB. H3OCl

C. KOH2

D. KOH2Cl

What salt forms from the reaction of hydrogen chloride, HCl, with potassium hydroxide, KOH?

A. KClB. H3OCl

C. KOH2

D. KOH2Cl

Explanation:

The K+ from the KOH combines with the Cl– from the HCl.

Relative Strengths of Acids and Bases

• Strong acids and bases ionize completely in water.

• Weak acids and bases do not ionize completely in water.

Acidic, Basic, and Neutral Solutions

Water can behave as an acid or a base.

In pure water, for every one hydronium ion, H3O+, formed, there is a hydroxide ion, OH–, formed.

So in pure water, [H3O+] = [OH–] = 0.0000001 M = 10–7 M.

So, in pure water, [H3O+] = [OH–] = 0.0000001 M = 10–7 M.

Add hydronium ions, H3O+, and the solution is “acidic,”

Add hydroxide ions, OH–, and the solution is “basic.”

As sodium hydroxide, NaOH, is added to water, the hydroxide ion, OH–, concentration

A. increases.B. decreases.C. remains the same.

Acidic, Basic, and Neutral SolutionsCHECK YOUR NEIGHBOR

As sodium hydroxide, NaOH, is added to water, the hydroxide ion, OH–, concentration

A. increases.B. decreases.C. remains the same.

Explanation:

The bond between sodium and oxygen is ionic. When dissolved in water, it separates into sodium ions and hydroxide ions, much like sodium chloride, NaCl, separates into sodium and chloride ions.

Acidic, Basic, and Neutral SolutionsCHECK YOUR ANSWER

pH is a measure of the concentration of hydronium ions, H3O+.

pH = –log [H3O+]

For pure water: pH = –log (10–7) pH = –(– 7) pH = 7

pH = –log [H3O+]

For pure water: pH = –log (10–7) pH = –(–7) pH = 7

What is a log?

The “log” of a number is simply the power to which ten is raised. The log of 103, for example, is 3.

Quiz Time

What is the log of 102?

Quiz Time

What is the log of 102?

Log 102 = 2

(the power to which 10 is raised)

103 = 1000

102 = 100

103 = 1000

102 = 100

101 = 10

103 = 1000

102 = 100

101 = 10

10–1 = 0.1

103 = 1000

102 = 100

101 = 10

10–1 = 0.1

10–2 = 0.01

103 = 1000

102 = 100

101 = 10

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

103 = 1000

102 = 100

101 = 10

100 = ?

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Three zeros

103 = 1000

102 = 100

101 = 10

100 = ?

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Two zeros

103 = 1000

102 = 100

101 = 10

100 = ?

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

One zero

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Zero zeros!

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1000 = ?

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1000 = ?

Log 103 =

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1000 = ?

Log 103 = 3

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1 = ?

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1 = ?

Log 100 =

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 1 = ?

Log 100 = 0

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 10–7 =

103 = 1000

102 = 100

101 = 10

100 = 1

10–1 = 0.1

10–2 = 0.01

10–3 = 0.001

Quiz Time

Log 10–7 = –7

pH = –log [H3O+]

For acidic water pH < 7, for example: pH = –log (10–5) pH = –(–5) pH = 5

pH = –log [H3O+]

For basic water pH > 7, for example: pH = –log (10–9) pH = –(–9) pH = 9

Acidic Rain and Basic Oceans

• Acid rain has a pH lower than 5.

2 SO2 (g) + O2 (g) SO3 (g)

SO3 (g) + H2O (l) H2SO4 (aq)

• Acid rain has a pH lower than 5.

• SO2 released from burning coal and oil.

2 SO2 (g) + O2 (g) SO3 (g)

SO3 (g) + H2O (l) H2SO4 (aq)

• CO2 levels in atmosphere rising

CO2 (g) + H2O (l) H2CO3 (aq)

Losing and Gaining Electrons

Acid–Base reactions: transfer of proton

Oxidation-Reduction reactions: transfer of ???

Oxidation-Reduction reactions: transfer of electron

Oxidation: The loss of an electron

2 Na 2 Na+ + 2 e–

Reduction: The gain of an electron

2 Na 2 Na+ + 2 e–

Cl2 + 2 e– 2 Cl–

2 Na 2 Na+ + 2 e–

Cl2 + 2 e– 2 Cl–

“Leo”

“Ger”

2 Na 2 Na+ + 2 e–

Cl2 + 2 e– 2 Cl–

“Leo”

“Ger”

“Ger

2 Na + Cl2 2 Na+ + 2 Cl–

What element within the reactants is oxidized in the following equation, and what element is reduced?

I2 + 2 Br – 2 I

– + Br2

A. Iodine, I, is oxidized, while the bromine ion, Br

–, is reduced.B. Iodine, I, is reduced, while the bromine ion, Br

–, is oxidized.C. Both the iodine, I, and the bromine ion, Br

–, are reduced.D. Both the iodine, I, and the bromine ion, Br

–, are oxidized.

Losing and Gaining ElectronsCHECK YOUR NEIGHBOR

I2 + 2 Br – 2 I– + Br2

A. Iodine, I, is oxidized, while the bromine ion, Br

–, is reduced.B. Iodine, I, is reduced, while the bromine ion, Br

–, is oxidized.C. Both the iodine, I, and the bromine ion, Br

–, are reduced.D. Both the iodine, I, and the bromine ion, Br

–, are oxidized.

Explanation:

Note how the iodine gains a negative charge, while the bromine loses the negative charge.

What element within the reactants is oxidized in the following equation and what element is reduced?

Losing and Gaining ElectronsCHECK YOUR ANSWER

Harnessing the Energy of Flowing Electrons

• Electric currents generated by oxidation-reduction reactions.

• Useful for:– Batteries– Fuel cells

• Ions must be able to flow to generate a current.

• A salt bridge allows this to happen.

• A battery is a self-contained voltaic cell.

• The positive electrode is the cathode, where reduction occurs.

• The negative electrode is the anode, where the oxidation occurs.

• Several types of batteries:– Dry cell– Alkaline– Rechargeable

• NiMH• Lithium

• Fuel cells convert the chemical energy of a fuel into electrical energy.

Electrolysis

• Electrolysis uses electrical energy to produce chemical change.

Electrolysis

• Electrolysis uses electrical energy to produce chemical change.

• Examples:– Recharging your car battery– Purifying metal ores

Electrolysis

Corrosion and Combustion

CorrosionThe process whereby a metal deteriorates through oxidation-reduction reactions.

CorrosionThe process whereby a metal deteriorates through oxidation-reduction reactions.It can be prevented by coating the metal with zinc, which oxidizes first.

CombustionAn oxidation-reduction reaction between a nonmetallic material, such as wood, and oxygen.

One of the products of combustion is water. Why doesn’t this water extinguish the combustion?

A. While areas of combustion are being extinguished, new areas are combusting.

B. Combustion only produces microscopic amounts of water. C. The chemical combustion reaction is happening too fast for the

water to have an effect on the fire.D. This water is in the gaseous phase and merely floats away.

Corrosion and CombustionCHECK YOUR NEIGHBOR

One of the products of combustion is water. Why doesn’t this water extinguish the combustion?

A. While areas of combustion are being extinguished, new areas are combusting.

B. Combustion only produces microscopic amounts of water. C. The chemical combustion reaction is happening too fast for the

water to have an effect on the fire.D. This water is in the gaseous phase and merely floats away.

Explanation:

Carefully place your hand over a campfire, and you can feel the greater humidity as water vapor escapes.

Corrosion and CombustionCHECK YOUR ANSWER

Hewitt/Suchocki/Hewitt Conceptual Physical Science …€¦ · PPT file · Web view ·...

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