Question 1

Why is the formation of iron hydroxide,Fe $( \mathrm { OH } ) _ { 2 }$ ,from $\mathrm { Fe } ^ { 2 + }$ and O $\mathrm { H } ^ { - }$ not considered an oxidation-reduction reaction?
A)The iron is only oxidized and nothing is reduced.
B)The iron is only reduced,not oxidized.
C)The $\mathrm { Fe } ^ { 2 + }$ ion is not changed during this chemical reaction.
D)Iron can never be oxidized or reduced.

Accepted Answer

In the formation of iron hydroxide from $\mathrm{Fe}^{2+}$ and $\mathrm{OH}^{-}$, the oxidation state of iron does not change; it remains +2 throughout the reaction, indicating no oxidation or reduction of iron occurs.

Question 2

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?
A)It would increase the rate of corrosion.
B)It would decrease the rate of corrosion.
C)The rate would stay the same.
D)Rates are only affected by temperature.
E)none of the above

Accepted Answer

When iron is connected to a more easily reducible metal like copper, it acts as the anode while the copper acts as the cathode. This creates a potential difference between the two metals and results in an increased flow of electrons from the iron to the copper. This causes accelerated corrosion of the iron, as more electrons are available for the oxidation reaction. Thus, connecting iron with a wire to a piece of copper would increase the rate of corrosion of the iron.

Question 3

Aluminum metal undergoes the same basic corrosion process that iron does yet it does not decompose as rapidly.Why?
A)The aluminum oxide does not flake off like rust and acts as a protective layer.
B)Aluminum is harder to oxidize than iron.
C)Aluminum is harder to reduce than iron.
D)The aluminum oxide product undergoes a reduction to produce aluminum metal.
E)The aluminum is galvanized,which prevents oxidation.

Accepted Answer

The aluminum oxide that forms on the surface of the metal does not flake off like rust does on iron. Instead, it forms a stable and protective layer that prevents further oxidation, thus slowing down the corrosion process. This is why aluminum does not decompose as rapidly as iron even though they both undergo the same basic corrosion process.

Question 4

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?
A)This was good news since the steel rivets prevented the copper from eroding.
B)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.
C)This combination of metals have no effect on each other and that is why engineers chose to use them together.
D)This combination of metals caused the copper to oxidize and turn green.

Accepted Answer

Because copper atoms have a greater tendency to be reduced than iron atoms, electrons will flow from the iron to the copper, accelerating corrosion around the interface of the two metals. This is bad news for the Statue of Liberty, whose copper exterior is held together by steel rivets.

Question 5

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 micro 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 from the fire.

Accepted Answer

The water produced during combustion is in the form of steam or water vapor, which is in the gaseous phase. This means it doesn't stay in contact with the fire to extinguish it but instead floats away from the heat source.

Question 6

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?
A)Oxygen in water is already "reduced" from the hydrogen atoms,so this oxygen atom no longer has a great attraction for additional electrons.
B)The oxygen is chemically bound to hydrogen atoms.
C)Oxygen in water is completely different from oxygen $\mathrm { O } _ { 2 }$ ,which is what is required for combustion.
D)all of the above

Accepted Answer

The oxygen in water is chemically bound to hydrogen atoms, making it unavailable for combustion processes. This means it cannot act as an oxidizer in the same way that free oxygen ($\mathrm{O}_2$) in the air does. The oxygen in water is in a "reduced" state due to its bond with hydrogen, meaning it does not have the same chemical properties or reactivity as molecular oxygen, which is necessary for fueling a fire.

Question 7

How does connecting a metal like iron with a wire to a metal that is easier to oxidize like zinc help prevent corrosion of the iron?
A)The other metal is oxidized instead and the electrons travel to the iron,keeping it from oxidizing.
B)The other metal absorbs the electrons from the iron,which keeps the iron from undergoing oxidation.
C)The wire is acting as an oxidant and keeps the two metals from undergoing other chemical reactions.
D)There is no salt-bridge,so there is no reaction between the two metals.
E)The other metal is oxidized and adsorbs all the oxidant,keeping it away from the iron.

Accepted Answer

Connecting a metal like iron with a wire to a metal that is easier to oxidize like zinc creates a galvanic cell. In this cell, the zinc acts as an anode and is oxidized, releasing electrons. These electrons travel through the wire to the iron, which acts as a cathode. The iron gains electrons and is protected from undergoing oxidation. Therefore, the other metal (zinc) is oxidized instead and the electrons travel to the iron, keeping it from oxidizing.

Question 8

How many electrons are transferred from iron atoms to oxygen atoms in the formation of two molecules of iron hydroxide,Fe $( \mathrm { OH } ) _ { 2 }$ ?
A)4 electrons
B)8 electrons
C)16 electrons
D)12 electrons

Accepted Answer

In the formation of two molecules of iron hydroxide, Fe(OH)₂, each iron (Fe) atom transfers 2 electrons to oxygen atoms. Since there are two Fe atoms in two molecules of Fe(OH)₂, a total of 4 electrons are transferred.

Question 9

The oxidation of iron to rust is a problem structural engineers need to be concerned about,but the oxidation of aluminum to aluminum oxide is not so much of a problem.Why?
A)Since aluminum is so light and inexpensive,it is easily replaced when corroded.
B)Aluminum oxide is insoluble in water and thus forms a protective coating that prevents continued oxidation of the aluminum.
C)Aluminum oxide is even stronger than aluminum.
D)The oxidation of aluminum is a very slow reaction,taking hundreds of years before any structural changes are noticed.

Accepted Answer

Aluminum oxide forms a protective coating that prevents continued oxidation of the aluminum. This coating is insoluble in water, which further protects the aluminum from corrosion. Therefore, the oxidation of aluminum to aluminum oxide is not as much of a problem for structural engineers as the oxidation of iron to rust.

Question 10

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}_? A)Iron is being oxidized. B)Oxygen is being oxidized. C)Oxygen is being reduced. D)Iron is being reduced. E)none of the above

Accepted Answer

At the anodic region, iron is being oxidized. This means that it is losing electrons, which are transferred to the cathodic region where oxygen is being reduced, gaining electrons. The overall reaction results in the formation of rust (Fe₂O₃), as the iron atoms react with oxygen and sulfur to form an oxide/sulfide compound.

Question 11

Why is the air over an open flame always moist?
A)The hot flame vaporizes the water in the air above the flame.
B)One of the products of combustion is water vapor.
C)Warm air contains more humidity than cold air.
D)None of the above is true.

Accepted Answer

When a substance is burned, including wood, gas, or other fuels used in an open flame, one of the products of combustion is water vapor, which is released into the air. This is why the air over an open flame is always moist.

Question 12

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?} A)Iron is being oxidized. B)Oxygen is being oxidized. C)Oxygen is being reduced. D)Iron is being reduced. E)none of the above

Accepted Answer

At the cathodic region, oxygen is being reduced. This reduces the available oxygen in the solution, allowing for the oxidation of iron to continue and leading to the formation of rust.

Question 13

Why are combustion reactions generally exothermic?
A)Hydrogen easily pulls electrons from the oxygen in water molecules and are reduced.
B)During combustion oxygen is oxidized,which gives off lots of energy.
C)Combustion involves the transfer of electrons to oxygen,which has an extremely high tendency for gaining electrons.
D)It is highly exothermic because combustion involves an oxidation-reduction reaction between a metallic material and oxygen.

Accepted Answer

Combustion reactions are exothermic because they involve the transfer of electrons to oxygen, which has a high affinity for electrons, releasing energy in the process.

Question 14

Iron atoms have a greater tendency to oxidize than do copper atoms.Is this good news or bad news for a home in which much of the plumbing consists of iron and copper pipes connected together? Explain.
A)This is bad news,since the iron atoms will be reduced by the copper atoms.
B)This is not a problem,since the strength of the copper will make up for the weakness of the iron.
C)It is bad news.The iron atoms will lose electrons to the copper atoms,which will pass those electrons onto oxygen atoms that are in contact with the surface.
D)This is not a problem since any electrons lost will be replaced by copper electrons.

Accepted Answer

The greater tendency of iron atoms to oxidize means that they are more likely to lose electrons, which will be picked up by the copper atoms. This can lead to corrosion of the pipes, especially in the presence of oxygen, which can react with the iron atoms to form iron oxide. Therefore, it is bad news for a home in which much of the plumbing consists of iron and copper pipes connected together. The loss of electrons cannot be replaced by copper electrons, so option D is incorrect. Option B is also incorrect because the strength of copper does not make up for the weakness of iron in terms of their tendency to oxidize. Option A is not correct as it uses the wrong terminology.

Question 15

A chemical equation for the combustion of propane,C₃H₈,is shown below.Through this reaction is the carbon oxidized or reduced? $\mathrm { C } _ { 3 }$ $\mathrm { H } _ { 8 }$ + 5 $\mathrm { O } _ { 2 }$ ? 3 $\mathrm { CO } _ { 2 }$ + 4 $\mathrm { H } _ { 2 }$ O A)The carbon is oxidized. B)The carbon is reduced. C)Some of the carbons are oxidized while others are reduced. D)The carbon is neither oxidized nor reduced.

Accepted Answer

In the reaction, carbon goes from a lower oxidation state in propane to a higher oxidation state in carbon dioxide, indicating oxidation.

Question 16

Upon combustion,about how many grams of water vapor are produced from every 16 grams of methane, $\mathrm { CH } _ { 4 }$ ? $\mathrm { CH } _ { 4 }$ + 2 $\mathrm { O } _ { 2 }$ ? $\mathrm { CO } _ { 2 }$ + 2 $\mathrm { H } _ { 2 }$ O
A)16 grams
B)18 grams
C)36 grams
D)8 grams

Accepted Answer

16 grams of methane react with 64 grams of oxygen to produce 44 grams of carbon dioxide and 36 grams of water vapor.

Question 17

Why is oxygen usually an oxidizing agent?
A)It is a very electronegative element.
B)It does not undergo reduction.
C)It likes to be oxidized.
D)It is very abundant and so it is easier to react than nitrogen.
E)all of the above

Accepted Answer

Oxygen is a very electronegative element, meaning that it has a strong attraction to electrons. This makes it likely for oxygen to accept electrons and be reduced, while oxidizing the other substance it is reacting with.

Quiz 18: Two Classes of Chemical Reactions

Why is the formation of iron hydroxide,Fe (OH) 2( \mathrm { OH } ) _ { 2 }(OH) 2​ ,from Fe2+\mathrm { Fe } ^ { 2 + }Fe2+ and O H−\mathrm { H } ^ { - }H− not considered an oxidation-reduction reaction?

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?

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

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?

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

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?

How does connecting a metal like iron with a wire to a metal that is easier to oxidize like zinc help prevent corrosion of the iron?

How many electrons are transferred from iron atoms to oxygen atoms in the formation of two molecules of iron hydroxide,Fe (OH) 2( \mathrm { OH } ) _ { 2 }(OH) 2​ ?

The oxidation of iron to rust is a problem structural engineers need to be concerned about,but the oxidation of aluminum to aluminum oxide is not so much of a problem.Why?

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?

Why is the air over an open flame always moist?

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?

Why are combustion reactions generally exothermic?

Iron atoms have a greater tendency to oxidize than do copper atoms.Is this good news or bad news for a home in which much of the plumbing consists of iron and copper pipes connected together? Explain.

A chemical equation for the combustion of propane,C3H8,is shown below.Through this reaction is the carbon oxidized or reduced? C3\mathrm { C } _ { 3 }C3​ H8\mathrm { H } _ { 8 }H8​ + 5 O2\mathrm { O } _ { 2 }O2​ ? 3 CO2\mathrm { CO } _ { 2 }CO2​ + 4 H2\mathrm { H } _ { 2 }H2​ O

Upon combustion,about how many grams of water vapor are produced from every 16 grams of methane, CH4\mathrm { CH } _ { 4 }CH4​ ? CH4\mathrm { CH } _ { 4 }CH4​ + 2 O2\mathrm { O } _ { 2 }O2​ ? CO2\mathrm { CO } _ { 2 }CO2​ + 2 H2\mathrm { H } _ { 2 }H2​ O

Why is oxygen usually an oxidizing agent?

Why is the formation of iron hydroxide,Fe $( \mathrm { OH } ) _ { 2 }$ ,from $\mathrm { Fe } ^ { 2 + }$ and O $\mathrm { H } ^ { - }$ not considered an oxidation-reduction reaction?

How many electrons are transferred from iron atoms to oxygen atoms in the formation of two molecules of iron hydroxide,Fe $( \mathrm { OH } ) _ { 2 }$ ?

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}_?

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?}

A chemical equation for the combustion of propane,C₃H₈,is shown below.Through this reaction is the carbon oxidized or reduced? $\mathrm { C } _ { 3 }$ $\mathrm { H } _ { 8 }$ + 5 $\mathrm { O } _ { 2 }$ ? 3 $\mathrm { CO } _ { 2 }$ + 4 $\mathrm { H } _ { 2 }$ O

Upon combustion,about how many grams of water vapor are produced from every 16 grams of methane, $\mathrm { CH } _ { 4 }$ ? $\mathrm { CH } _ { 4 }$ + 2 $\mathrm { O } _ { 2 }$ ? $\mathrm { CO } _ { 2 }$ + 2 $\mathrm { H } _ { 2 }$ O