AP Chemistry : Electrochemistry

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #101 : Reaction Types

Consider the following electrolytic cell:

      

What happens at the anode in the electrolytic cell?

Possible Answers:

Iron is reduced

Nickel is oxidized

Iron is oxidized

Nickel is reduced

Correct answer:

Nickel is oxidized

Explanation:

It does not matter if the cell is galvanic or electrolytic; oxidation will always take place at the anode. This means that the nickel loses two electrons and is oxidized at the anode to generate nickel ions.

Nickel ions and iron are products, and are neither oxidized nor reduced during the reaction. Iron ions are reduced at the cathode to generate the iron product.

Example Question #102 : Reaction Types

Consider the following reaction in a galvanic cell:

 

Which of the following takes place at the anode?

Possible Answers:

Zinc is reduced

Copper is reduced

Copper is oxidized

No reaction takes place at the anode

Zinc is oxidized

Correct answer:

Zinc is oxidized

Explanation:

Oxidation takes place at the anode and reduction takes place at the cathode. You can remember this with the pneumonic "An Ox, Red Cat."

In the equation, zinc loses electrons. It goes from a neutral, elemental charge to a charge of . Since electrons are negative, a loss of electrons will cause an increase in charge. Because zinc loses electrons, it is oxidized. This will take place at the anode.

Example Question #511 : Ap Chemistry

Toward which pole do electrons travel in a galvanic cell?

Possible Answers:

Towards the anode

More information is needed

Electrons do not travel; only the protons travel

Towards the cathode

Towards the negative pole

Correct answer:

Towards the cathode

Explanation:

Reduction always occurs at the cathode, and oxidation always occurs at the anode. Since reduction is the addition of electrons, the electrons must flow toward the site of reduction.

In a galvanic cell the positive charge is on the cathode, while the negative charge is on the anode. Since a galvanic cell has a positive potential and is spontaneous, electrons freely flow down their potential gradient. The electrons, which are negatively charged, are traveling towards the cathode, which is positive charged, since opposites attract.

Example Question #1 : Electrochemistry

Toward which pole do the electrons travel in an electrolytic cell?

Possible Answers:

Towards the positive pole

More information is needed

The electrons do not travel; only the protons travel

Towards the anode

Towards the cathode

Correct answer:

Towards the cathode

Explanation:

Reduction always occurs at the cathode, and oxidation always occurs at the anode. Since reduction is the addition of electrons, electrons must travel toward the site of reduction.

In an electrolytic cell the negative charge is on the cathode, while the positive charge is on the anode. Since an electrolytic cell requires energy to perpetuate the reaction, we are pushing the electrons against their potential gradient. The electrons, which are negatively charged, are traveling towards the cathode, which is also negatively charged.

Example Question #2 : Electrochemistry

Which of the following differences between galvanic cells and electrolytic cells is false?

Possible Answers:

Electrolytic cells have oxidation take place at the cathode

Electrolytic cells have negative voltages

Electrolytic cells have a positive Gibb's free energy

Electrolytic cells are non-spontaneous

Correct answer:

Electrolytic cells have oxidation take place at the cathode

Explanation:

Electrolytic cells use non-spontaneous reactions that require an external power source in order to proceed. The values between galvanic and electrolytic cells are opposite of one another. Galvanic cells have positive voltage potentials, while electrolytic voltage potentials are negative. Both types of cell, however, have oxidation occur at the cathode and reduction occur at the anode.

Example Question #2 : Electrochemistry

What is true about the current flow in a galvanic cell?

Possible Answers:

It travels from cathode to anode

It travels from anode to cathode

It flows in the direction of electron flow

Galvanic cells do not have a current

Correct answer:

It travels from cathode to anode

Explanation:

In a galvanic cell, the electrons will flow from the anode to the cathode; however, current travels in the opposite direction of the electrons by convention. In chemical cells, current is defined by the direction in which protons would flow. As a result, current flows from the cathode to the anode.

Keep in mind that reduction occurs at the cathode and oxidation occurs at the anode. Electrons are thus constantly moving from the anode to the cathode. Since the current will be opposite to the flow of electrons, we can conclude that it must flow from cathode to anode.

Example Question #1 : Electrochemistry

The following galvanic cell is created:

      

Which of the following takes place at the cathode?

Possible Answers:

Gold ions receive electrons

Copper gains electrons

Copper loses electrons

Gold loses electrons

Correct answer:

Gold ions receive electrons

Explanation:

Reduction always takes place at the cathode. This means that a substance is receiving electrons.

In the reaction, the gold ions are receiving electrons in order to create gold atoms. This takes place at the cathode.

Copper ions and gold are products, and will not be oxidized or reduced. Copper is reduced at the anode during this reaction.

Example Question #515 : Ap Chemistry

1.  

2.  

3. 

What is ? Is reaction 3 spontaneous?

Possible Answers:

, spontaneous

, spontaneous

, nonspontaneous

, nonspontaneous

Correct answer:

, nonspontaneous

Explanation:

There are two concepts to consider in this problem.  First, the question asks for the .  Reaction 3 has  being reduced so the potential for the half reaction becomes negative.  half reaction appears the same in reaction 3 so the potential is the same. Second, negative voltages indicate non-spontaneity and positive voltages are spontaneous.  

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