In a galvanic cell, electrons flow through the external wire from the anode to the cathode.
Correct Answer
True
True. Electrons are released by oxidation at the anode, travel through the external circuit, and are consumed by reduction at the cathode.
Category: Galvanic Cells
Question 2
A reducing agent gains electrons during a redox reaction.
Correct Answer
False
False. A reducing agent loses electrons and is itself oxidized; the oxidizing agent is the species that gains electrons.
Category: Redox Balancing
Question 3
In an electrolytic cell, the anode is the positive electrode.
Correct Answer
True
True. The external power source pulls electrons away from the anode, making it positive, and pushes them onto the cathode, making it negative. This is the reverse of the electrode signs in a galvanic cell.
Category: Electrolysis
Question 4
Multiplying a half-reaction by 2 doubles its standard reduction potential.
Correct Answer
False
False. A standard potential is an intensive property that does not depend on the amount of substance, so it stays the same when a half-reaction is multiplied by any coefficient.
Category: Cell Potentials
Question 5
The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge of the ion.
Correct Answer
True
True. Oxidation numbers are assigned so that they add up to zero for a neutral compound and to the ion's charge for an ion, which is how an unknown oxidation number is found.
Category: Redox Balancing
Question 6
A galvanic cell uses an external power source to drive a nonspontaneous reaction.
Correct Answer
False
False. A galvanic cell produces electricity from a spontaneous redox reaction. An electrolytic cell is the type that uses external power to drive a nonspontaneous reaction.
Category: Galvanic Cells
Question 7
The standard hydrogen electrode consists of a platinum electrode in contact with hydrogen gas and H+ ions.
Correct Answer
True
True. The platinum provides an inert surface on which H2 and H+ are interconverted, with 1 M H+ and hydrogen at standard pressure, and the electrode is assigned a potential of 0 V.
Category: Cell Potentials
Question 8
Rust that forms on iron is a hydrated iron(II) oxide.
Correct Answer
False
False. Rust is a hydrated iron(III) oxide, Fe2O3 with a variable amount of water. Iron is first oxidized to Fe2+, which oxygen and water then oxidize further to the +3 state.
Category: Corrosion
Question 9
The patina that forms on copper exposed to air protects the metal beneath it from further corrosion.
Correct Answer
True
True. The green and blue copper compounds that make up the patina form a stable layer that shields the metal, a process called passivation. Rust on iron, by contrast, flakes off and exposes fresh metal.
Category: Corrosion
Question 10
Paint protects iron from rusting by acting as a sacrificial anode.
Correct Answer
False
False. Paint works as a barrier that keeps water and oxygen away from the iron. A sacrificial anode is a more active metal, such as zinc or magnesium, that is oxidized in place of the iron.
Category: Corrosion
Question 11
The zinc can of a common dry cell battery serves as its anode.
Correct Answer
True
True. In a zinc-carbon dry cell, the zinc container is oxidized to Zn2+, while manganese dioxide in a paste around a graphite rod is reduced at the cathode.
Category: Batteries and Fuel Cells
Question 12
A nickel-cadmium battery is a primary battery that cannot be recharged.
Correct Answer
False
False. A nickel-cadmium battery is a secondary battery; its reaction can be reversed by an external current, so it can be recharged many times.
Category: Batteries and Fuel Cells
Question 13
A fuel cell converts the chemical energy of its fuel into useful energy more efficiently than an internal combustion engine does.
Correct Answer
True
True. Fuel cells convert roughly half or more of the fuel's energy into electrical energy, while a gasoline engine converts only about a fifth to a quarter into work, losing the rest as heat.
Category: Batteries and Fuel Cells
Question 14
In the electrolysis of water, hydrogen gas is produced at the anode.
Correct Answer
False
False. Hydrogen gas is produced at the cathode, where H+ ions or water molecules are reduced. Oxygen gas forms at the anode, where water is oxidized.
Category: Electrolysis
Question 15
The amount of metal deposited during electrolysis is proportional to the total charge passed through the cell.
Correct Answer
True
True. Each mole of metal requires a fixed number of moles of electrons, so the moles of metal deposited equal the charge divided by the Faraday constant and by the electrons needed per ion.
Category: Electrolysis
Question 16
When a spoon is silver plated by electrolysis, the spoon serves as the anode.
Correct Answer
False
False. The spoon is the cathode, where Ag+ ions gain electrons and are deposited as silver metal. A piece of silver serves as the anode and is oxidized to replace the Ag+ ions in solution.
Category: Electrolysis
Question 17
An alkaline battery uses potassium hydroxide as its electrolyte.
Correct Answer
True
True. An alkaline battery uses a basic potassium hydroxide electrolyte with a zinc anode and a manganese dioxide cathode, unlike the acidic ammonium chloride paste of a zinc-carbon dry cell.
Category: Batteries and Fuel Cells
Question 18
A 12 V lead acid car battery consists of three cells connected in series.
Correct Answer
False
False. Each lead acid cell produces about 2 V, so a 12 V car battery contains six cells connected in series.
Category: Batteries and Fuel Cells
Question 19
In a balanced redox equation, the number of electrons lost in oxidation equals the number of electrons gained in reduction.
Correct Answer
True
True. Electrons cannot be created or destroyed, so the half-reactions are multiplied by factors that make the electrons lost and gained equal before they are added together.
Category: Redox Balancing
Question 20
In standard cell notation, the cathode half-cell is written on the left.
Correct Answer
False
False. By convention the anode half-cell is written on the left and the cathode half-cell on the right, separated by a double line for the salt bridge.
Category: Galvanic Cells