The process in which a species loses electrons, raising the charge assigned to its atoms, is called oxidation.
Missing Word
oxidation
Oxidation is the loss of electrons, which increases a species' oxidation number. It always occurs together with reduction, the gain of electrons, in a redox reaction.
Category: Redox Balancing
Question 2
In any electrochemical cell, the electrode where reduction takes place is the cathode.
Missing Word
cathode
The cathode is defined as the electrode at which reduction occurs, in both galvanic and electrolytic cells. The anode is where oxidation occurs.
Category: Galvanic Cells
Question 3
The charge carried by one mole of electrons, about 96,485 C, is called the Faraday constant.
Missing Word
Faraday
The Faraday constant, F, converts between moles of electrons and electric charge. It appears in both delta G = -nFE and in electrolysis calculations.
Category: Free Energy and Equilibrium
Question 4
The Nernst equation gives the cell potential under nonstandard conditions from the standard cell potential, the temperature, and the reaction quotient.
Missing Word
Nernst
The Nernst equation, E = E standard - (RT/nF) ln Q, shows how cell potential changes as concentrations change. At equilibrium Q equals K and the cell potential becomes zero.
Category: Free Energy and Equilibrium
Question 5
Using an external source of electrical energy to force a nonspontaneous redox reaction to occur is called electrolysis.
Missing Word
electrolysis
Electrolysis is carried out in an electrolytic cell, where an applied voltage drives a reaction with a negative cell potential. It is used to produce sodium and chlorine, refine metals, and recharge batteries.
Category: Electrolysis
Question 6
The gradual degradation of a metal by a natural electrochemical process, such as the rusting of iron, is called corrosion.
Missing Word
corrosion
Corrosion is the oxidation of a metal by substances in its environment, usually oxygen and water. Tarnish on silver and the patina on copper are other examples.
Category: Corrosion
Question 7
The formation of a thin, stable surface layer that shields a metal from further attack by air and water is called passivation.
Missing Word
passivation
Passivation produces a protective coating, such as the patina on copper or the chromium oxide film on stainless steel. Rust on iron does not passivate because it flakes away.
Category: Corrosion
Question 8
Galvanized iron is coated with a layer of zinc, a metal that is oxidized more readily than iron.
Missing Word
zinc
Zinc protects iron both as a barrier and, if the coating is scratched, by being oxidized in place of the iron. This works because zinc has a lower reduction potential than iron.
Category: Corrosion
Question 9
The SI unit of electric charge, equal to the charge carried by a current of one ampere flowing for one second, is the coulomb.
Missing Word
coulomb
The coulomb is the unit of charge, and charge equals current multiplied by time (Q = It). Dividing the charge passed in an electrolysis by the Faraday constant gives the moles of electrons transferred.
Category: Electrolysis
Question 10
In both the common dry cell and the alkaline battery, the substance reduced during discharge is an oxide of the transition metal manganese.
Missing Word
manganese
Both batteries use manganese dioxide, MnO2, which is reduced to Mn2O3 at the cathode while zinc is oxidized at the anode. The two differ mainly in their electrolyte: an ammonium chloride paste in the dry cell and potassium hydroxide in the alkaline battery.
Category: Batteries and Fuel Cells
Question 11
Stainless steel resists rusting because it is alloyed with chromium, a metal that forms a protective oxide film.
Missing Word
chromium
Chromium in stainless steel reacts with oxygen to form a thin, adherent oxide layer that passivates the surface and keeps the iron from rusting.
Category: Corrosion
Question 12
In the fuel cells used on extended space missions, the fuel consumed is hydrogen gas, and the only product is water.
Missing Word
hydrogen
A hydrogen fuel cell oxidizes hydrogen at the anode and reduces oxygen at the cathode, producing about 1.2 V. Because water is the only chemical product, the cell produces no carbon dioxide.
Category: Batteries and Fuel Cells
Question 13
In the rechargeable batteries of most phones and laptops, the ions that shuttle between the graphite electrode and the cobalt oxide electrode are lithium ions.
Missing Word
lithium
A lithium-ion battery works by moving lithium ions between a graphite electrode and a lithium cobalt oxide electrode. The process reverses during charging, which makes the battery rechargeable.
Category: Batteries and Fuel Cells
Question 14
When iron rusts in moist air, the region of the metal where iron atoms are oxidized to Fe2+ ions acts as the anode.
Missing Word
anode
Rusting is an electrochemical process: one region of the iron surface acts as the anode, where iron loses electrons, while another region acts as the cathode, where oxygen is reduced.
Category: Corrosion
Question 15
Depositing one mole of aluminum metal from aluminum(III) ions requires 3 moles of electrons.
Missing Word
3
Each aluminum(III) ion carries a charge of +3, so it must gain 3 electrons to become a neutral aluminum atom. This ratio of electrons to metal atoms is needed to convert charge into mass in electrolysis.
Category: Electrolysis