CHAPTER 18

How many electrons are gained or lost in the following half-reaction? Na → Na+

1 electron is lost

Which of the following reactions illustrates an amphoteric compound?

2 HF ↔ H2F+ + F-

How many electrons are gained or lost in the following half-reaction? Cl2 → 2 Cl-

2 electrons are gained

If you had a 1 M solution of a weak acid what would be its pH?

6

Water is formed from the reaction of an acid and a base. Why is it not classified as a salt?

A salt is an ionic compound, whereas water is a covalent compound.

Which of the following statements about strong or weak acids is true?

A weak acid will react with a strong base.

What is one of the advantages of a fuel cell?

All (They can run for a very long time as long as you keep adding fuel. They are more efficient than combustion. They have lower emission of pollutants than combustion.)

The following set of redox reactions takes place as shown. Container A Container BFe → Fe+2 + 2e- Cu+2 + 2e- → Cu If you had two containers filled with the ion solution described above with a wire connecting a piece of iron (in container A) and a piece of copper (in container B) and a salt-bridge connecting the two containers, describe what happens.

All of the iron is transformed into iron ions and all of the copper ions are transformed into copper metal.

What does the value of Kw say about the extent to which water molecule react with themselves?

Because the value of Kw is so small, the extent to which water ionizes is quite small.

Which of the above images represents a solution of the strongest acid (HA)?

C

Which of the following species is undergoing reduction? 2 CuBr → 2Cu + Br2

Cu+

Copper atoms have a greater tendency to be reduced than iron atoms do. Was this good news or bad news for the Statue of Liberty, whose copper exterior was originally held together by steel rivets?

Electrons will preferentially flow from the iron to the copper and then onto oxygen. Corrosion is thus accelerated around the interface of these two metals.

In one type of fuel cell the following oxidation-reduction reactions are taking place: 2 H2 + O2 → 2 H2O What is the fuel?

H2

For the following acid-base reaction, identify what is formed in the space marked. H2SO4 + KOH ↔ KHSO4 + ???

H2O

According to the following reaction, which molecule is acting as an acid? H2O + H2SO4 → H3O+ + HSO4-

H2SO4

Rust has a tendency to form when iron in contact with water reacts according to the following reaction: 4 Fe + 3 O2 → 2 Fe2O3 What is happening at the anodic region?

Iron is being oxidized.

Why is oxygen usually an oxidizing agent?

It is a very electronegative element.

How would connecting iron with a wire to a piece of metal like copper, which undergoes reduction very easily, affect the rate at which the iron corrodes?

It would increase the rate of corrosion.

For the following acid-base reaction, identify what is formed in the space marked HF + KOH ↔ ???? + H2O

KF

For the following acid-base reaction, identify what compound is formed in the space marked. HNO3 + KOH ↔ ???? + H2O

KNO3

A weak acid is added to a concentrated solution of hydrochloric acid. Does the solution become more or less acidic?

Less acidic, since the solution becomes more dilute with a less concentrated solution of hydronium ions being added to the solution

In a battery, the following oxidation-reduction reactions are taking place: Mn2O3 + ZnO → 2 MnO2 + Zn What is being formed at the anode?

MnO2

In a battery, the following two oxidation-reduction reactions are taking place: rxn A: Zn + 2 OH- → ZnO + H2O + 2erxn B: 2 MnO2 + H2O + 2e- → Mn2O3 + 2 OHWhat is undergoing reduction?

MnO2

Which of the following statements about oxidation and reduction reactions is true?

More than one electron can be transferred in an oxidation and reduction reaction.

For the following acid-base reaction, identify which salt is formed. HCl + NaOH ↔ ???? + H2O

NaCl

Qualitatively, what happens to the hydronium ion concentration if you increase the hydroxide ion concentration?

None of these (The concentration of H3O+ increases but the ratio stays the same. The concentration of H3O+ increases to neutralize the excess hydroxide. The concentration of H3O+ stays the same but the ratio changes.)

According to the following reaction, which molecule is acting as a base? OH- + NH4+ → H2O + NH3

OH-

Water is 88.88 percent oxygen by mass. Oxygen is exactly what a fire needs to grow brighter and stronger. So why doesn't a fire grow brighter and stronger when water is added to it?

Oxygen in water is already "reduced" from the hydrogen atoms, so this oxygen atom no longer has a great attraction for additional electrons. The oxygen is chemically bound to hydrogen atoms. Oxygen in water is completely different from oxygen O2, which is what is required for combustion. (all of the above)

Rust has a tendency to form when iron in contact with water reacts according to the following reaction: 4 Fe + 3 O2 → 2 Fe2O3 What is happening at the cathodic region?

Oxygen is being reduced

Hydrogen sulfide, H2S, burns in the presence of oxygen, O2, to produce water, H2O, and sulfur dioxide, SO2. Through this reaction, is sulfur oxidized or reduced? 2 H2S + 3 O2 → 2 H2O + 2 SO2

Sulfur is oxidized.

Aluminum metal undergoes the same basic corrosion process that iron does yet it does not decompose as rapidly. Why?

The aluminum oxide does not flake off like rust and acts as a protective layer.

Suggest why people once washed their hands with ashes.

The ashes act as a base and reacts with skin oils to produce solutions of soap.

A chemical equation for the combustion of propane, C3H8, is shown below. Through this reaction is the carbon oxidized or reduced? C3H8 + 5 O2 → 3 CO2 + 4 H2O

The carbon is oxidized.

Qualitatively, what happens to the hydronium ion concentration if you increase the hydroxide ion concentration?

The concentration of H3O+ stays the same but the ratio changes. The concentration of H3O+ increases to neutralize the excess hydroxide. The concentration of H3O+ increases but the ratio stays the same (none of the above)

The following set of redox reactions takes place when iron is dipped in a solution of copper ions. Fe → Fe+2 + 2e-Cu+2 + 2e- → Cu Which of the following describes what is happening on the surface of the iron?

The copper starts to plate out on iron.

What happens to the corrosive properties of an acid and a base after they neutralize each other? Why?

The corrosive properties are neutralized because the acid and base no longer exist.

How might electrolysis be used to raise the hull of a sunken ship?

The gaseous products of the electrolysis of water could be collected with large bags attached to the hull of the ship. As the bags inflate with the gas they are buoyed upward pulling the ship also upward.

The general chemical equation for photosynthesis is shown below. Through this reaction are the oxygens of the water molecules, H2O, oxidized or reduced? 6 CO2 + 6H2O → C6H12O6 + 6 O2

The oxygens of the water molecules are oxidized.

The main component of bleach is sodium hypochlorite, NaOCl, which consists of sodium ions, Na+, and hypochlorite ions, - OCl What products are formed when this compound is reacted with the hydrochloric acid, HCl, of toilet bowl cleaner?

The products are NaCl and HOCl.

What element is oxidized in the following equation and what element is reduced? Sn2+ + 2 Ag → Sn + 2 Ag+

The tin ion, Sn2+, is reduced, while the silver, Ag, is oxidized

Why does a battery that has thick zinc walls last longer than one that has thin zinc walls?

The zinc walls are transformed into zinc ions as the battery provides electricity.

In a battery, the following oxidation-reduction reaction is taking place: Mn2O3 + ZnO → 2 MnO2 + Zn What is undergoing reduction as written?

ZnO

Which of the following statements describes a basic solution?

[H3O+] < [OH-]

Which of the following solutions is the most acidic? a solution with a pH = 13 a solution with a pH = 7 a solution with a pH = 14 a solution with a pH = 12 All of the solutions are basic.

a solution with a pH = 7

If you had a 1 M solution of a strong acid what would be its pH?

a.)13 b.)8 c.)0 d.)1 e.)7 Answer: C

Which of the following statements about electrochemistry is not true?

a.)It is the study of how electrons are transferred from one chemical compound to another. b.)It involves the use of electrical current to produce an oxidation-reduction reaction. c.)It involves the use of a set of oxidation-reduction reactions to produce electrical current. d.)It is the study of how electrical energy and chemical reactions are related. e.)All of the above are true. Answer: E

What is a base?

anything that accepts a hydrogen ion

For the following reaction, identify whether the compound in bold is behaving as an acid or a base. H3PO4 + H2O ↔ H2PO4- + H3O+

base

As the pH increases, the hydroxide ion concentration

gets larger.

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

hydrogen ion

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

hydrogen ion

In a battery, the following two oxidation-reduction reactions are taking place: rxn A: Zn → Zn+2 + 2e- rxn B: 2 NH4+ + 2e- → 2 NH3 + H2 Which reaction is taking place at the anode?

rxn A

What is a reduction?

the gain of electrons

What is the purpose of a salt-bridge?

to allow ions to migrate between solutions