cathode

(noun)

The electrode of an electrochemical cell at which reduction occurs.

Related Terms

Examples of cathode in the following topics:

  • Cathode Rays

    • Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube.
    • These were the cathode rays.
    • Eugene Goldstein named them cathode rays.
    • Thomson studied cathode ray tubes and came up with the idea that the particles in the cathode beams must be negative because they were repelled by negatively charged items (either the cathode or a negatively charged plate in the cathode ray tube) and attracted by positively charged items (either the anode or the positively charged plate in the cathode ray tube).
    • It was used in discovery of cathode rays.

  • Voltaic Cells

    • The cathode is the electrode where reduction takes place.
    • The anode will undergo oxidation and the cathode will undergo reduction.
    • At the cathode, the metal ion in the solution will accept one or more electrons from the cathode, and the ion's oxidation state will reduce to 0.
    • This forms a solid metal that deposits on the cathode.
    • Copper readily oxidizes zinc; the anode is zinc and the cathode is copper.

  • Electrochemical Cell Notation

    • .), the anode, the cathode, and the electrode components are all described in this unique shorthand.
    • Recall that oxidation takes place at the anode and reduction takes place at the cathode.
    • When the anode and cathode are connected by a wire, electrons flow from anode to cathode.
    • In the reaction, the silver ion is reduced by gaining an electron, and solid Ag is the cathode.
    • The anode half-cell is described first; the cathode half-cell follows.

  • The Lithium-Ion Battery

    • The three participants in the electrochemical reactions in a lithium-ion battery are the anode, the cathode, and the electrolyte.
    • Both the anode, which is a lithium-containing compound, and the cathode, which is a carbon-containing compound, are materials into which lithium ions can migrate.
    • When a lithium-based cell is discharging, the positive lithium ion is extracted from the cathode and inserted into the anode, releasing stored energy in the process.
    • The most commercially popular cathode material is graphite.
    • In a lithium-ion battery, the lithium ions are transported to and from the cathode or anode.

  • Electrolysis of Water

    • Multiplying the cathode reaction by 2, in order to match the number of electrons transferred, results in this net equation, after OH- and H+ ions combine to form water:
    • Hydrogen will appear at the cathode, the negatively charged electrode, where electrons enter the water, and oxygen will appear at the anode, the positively charged electrode.

  • Electrolytic Properties

    • Another reaction occurs at the anode, producing electrons that are eventually transferred to the cathode.
    • As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode.
    • For example, in a solution of ordinary table salt (sodium chloride, NaCl) in water, the cathode reaction will be:
    • Two mnemonics for remembering that reduction happens at the cathode and oxidation at the anode are: "Red Cat" (reduction - cathode) and "An Ox" (anode - oxidation).
    • For example, p-Benzoquinone can be reduced to hydroquinone at the cathode:

  • Preventing Corrosion

    • Corrosion of the sacrificial zinc results in its oxidation; the iron is reduced, which renders it cathodic and inhibits its corrosion.
    • This method is referred to as cathodic protection.
    • Cathodic protection replicates the effects of a sacrificial coating but with a more active metal.
    • Cathodic protection is used to protect underground fuel tanks and pipelines, among other things.
    • The galvanic anode continues to corrode, consuming the anode material until eventually it must be replaced, but the cathodic material is protected.

  • Corrosion

    • The conductivity allows electrons to flow from the anodic to cathodic regions of the metal.
    • The free electrons reduce the electron acceptor, resulting in any of the following cathodic steps:

  • Electrolysis of Sodium Chloride

    • Sodium ions migrate to the cathode, where electrons enter the melt and are reduced to sodium metal:
    • Liquid sodium floats to the top of the melt above the cathode and is drained off into a storage tank.
    • At the cathode (C), water is reduced to hydroxide and hydrogen gas.

  • Predicting the Products of Electrolysis

    • Positively charged ions, or cations, move toward the electron-providing cathode, which is negative; negatively charged ions, or anions, move toward the positive anode.
    • You may have noticed that this is the opposite of a galvanic cell, where the anode is negative and the cathode is positive.
    • Oxidation of ions or neutral molecules occurs at the anode, and reduction of ions or neutral molecules occurs at the cathode.
    • It is also possible to reduce ferricyanide ions to ferrocyanide ions at the cathode:
    • This is because Cu2+ ions are attracted to the negatively charged cathode, and since the the cathode is putting out electrons, the Cu2+ becomes reduced to form copper metal, which is deposited on the electrode.