combustionBurning: the fast oxidation of a fuel. The fuel is the reducing agent, and oxygen from the air is usually the oxidizing agent. Methane burns to carbon dioxide and water.
corrosionDamage to a metal as it reacts with air or water. It turns a refined metal into a more stable form such as an oxide. Paint, oil and plating slow it by keeping air and water off the metal.
electronThe particle that changes hands in a redox reaction. It carries one unit of negative charge. A proton is almost 2,000 times as heavy.
half-reactionThe oxidation or the reduction, written by itself. In a zinc and copper cell, zinc atoms giving up electrons is one half-reaction and copper ions taking them is the other.
oxidationLosing electrons, as iron does when it rusts. The older meaning is gaining oxygen. The oxidation state of an atom goes up when it is oxidized.
oxidation stateAn atom's charge if every bond it has were ionic. It is also called the oxidation number. In potassium chloride, potassium is +1 and chlorine is -1; in a pure element it is zero.
Show all 36 terms (30 more)
Oxidation and reduction, continued
oxideWhat forms when oxygen bonds to a metal or nonmetal. Most of Earth's crust is made of oxides. A thin skin of aluminum oxide protects aluminum foil from the air.
oxidizing agentThe electron taker in a reaction; it gets reduced. It is also called an oxidant or an oxidizer. Oxygen, hydrogen peroxide and the halogens are common ones.
redox reactionOxidation and reduction taking place as a pair. The name is a blend of reduction and oxidation, first printed in 1928. Neither half happens alone.
reducing agentThe electron giver in a reaction; it gets oxidized. It is also called a reductant. Hydrogen, carbon monoxide and the alkali metals are common ones.
reductionGaining electrons, as a metal ion does in plating. The older meaning is losing oxygen, as copper oxide does when hydrogen turns it to copper. The oxidation state of a reduced atom goes down.
rustHydrated iron oxide, the product of iron corroding. Iron rusts only where both oxygen and water reach it. Rust is flaky and falls away, so the iron under it goes on rusting.
Cells and electrolysis 12
anodeThe electrode at which electrons are given up. Oxidation happens here. It is the negative terminal of a battery in use and the positive electrode in electrolysis.
batteryCells joined in one unit that has two terminals. It runs until one of its chemicals is used up. In a rechargeable battery an outside current restores them.
cathodeThe electrode at which electrons are taken up. Reduction happens here. In electroplating, the object to be coated is the cathode.
electrodeA solid conductor dipped into an electrolyte. Michael Faraday coined the word in 1833. An electrode is called an anode or a cathode by the direction of the current.
electrolysisUsing electric current to force a reaction to run. It splits water into hydrogen gas and oxygen gas. Aluminum is won from molten aluminum oxide this way.
electrolyteA substance that conducts by ions, not electrons. Most salts, acids and bases dissolved in water are electrolytes. The dissolved substance splits into positive and negative ions.
electroplatingCoating an object with metal by electrolysis. Metal ions in the solution gain electrons and settle on the object as a thin layer. Steel cutlery is plated with silver this way.
fuel cellA cell fed fuel and oxygen from outside as it runs. It makes electricity for as long as it is supplied. A hydrogen fuel cell gives off nothing but water and heat.
galvanic cellA cell whose own redox reaction pushes a current. It is also called a voltaic cell. The names honor Luigi Galvani and Alessandro Volta. Volta built the first electric battery.
half-cellOne electrode with the electrolyte around it. A galvanic cell is made of two. Oxidation happens in one and reduction in the other.
salt bridgeA link of salt solution joining two half-cells. It can be a strip of filter paper soaked in a salt solution. Ions move through it, which completes the circuit.
voltageHow hard a cell or battery drives its current. It is measured in volts. Common batteries give 1.5 volts or 9 volts.
Metals and everyday redox 12
anodizingThickening a metal's oxide skin by electrolysis. The part is made the anode of a cell, which gives the process its name. Anodized aluminum can soak up dye, so it comes in many colors.
antioxidantA compound added to stop a product oxidizing. Antioxidants are added to foods to keep oils and fats from turning rancid, and to fuels, plastics and lubricants to make them last.
displacement reactionA more reactive element taking another's place. An iron nail in copper sulfate solution gets a pinkish-brown coat of copper: the iron has pushed the copper out of its compound.
disproportionationOne substance being both oxidized and reduced. Hydrogen peroxide does this as it breaks down: part of its oxygen ends up in water and part as oxygen gas.
galvanizationZinc-coating steel, usually in a bath of molten zinc. Zinc, the more reactive metal, oxidizes before the iron does. The steel stays protected even where the zinc is scratched.
passivationA metal growing its own thin shield of oxide. The film forms as the bare metal meets the air. It is why aluminum, which is a reactive metal, does not seem to corrode.
patinaThe green coat that weather gives old copper. It also forms on bronze and brass. A patina can protect the metal under it from further corrosion.
reactivity seriesMetals ranked by how readily they react. Potassium and sodium are near the top; gold and platinum are at the bottom. It predicts which metal will displace which.
sacrificial anodeA block of reactive metal fixed on to corrode first. Blocks of zinc, aluminum or magnesium protect ship hulls and buried pipes. Once a block has corroded away it is replaced.
smeltingHeating ore with carbon so the metal is set free. The carbon, as coke or charcoal, is the reducing agent. Iron, copper, tin, lead and zinc are all won this way.
stainless steelSteel with enough chromium to resist rusting. It holds at least 10.5 percent chromium. The chromium forms a thin film that heals itself when the surface is scratched.
tarnishThe thin gray-black coat that dulls silverware. The reaction stops after the outermost layers of metal, so tarnish, unlike rust, does not eat inward. Silver needs a sulfur gas, hydrogen sulfide, to tarnish.
How this list was compiled: Term list chosen for this site on 2026-10-12. Each meaning is written in our own words and was checked that day against the article on the term in the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Redox, Electron, Oxidizing agent, Reducing agent, Corrosion, Rust, Oxidation state, Half-reaction, Oxide, Combustion, Electrode, Anode, Cathode, Electrolyte, Galvanic cell, Half-cell, Salt bridge, Electrolysis, Electrolysis of water, Electroplating, Electric battery, Fuel cell, Voltage, Tarnish, Patina, Galvanization, Galvanic anode, Reactivity series, Single displacement reaction, Smelting, Antioxidant, Passivation (chemistry), Disproportionation, Stainless steel and Anodizing. The two meanings of oxidation and of reduction, rust as hydrated iron oxide and the need for both oxygen and water, the barriers that slow rusting, electroplating with silver, sacrificial metals and galvanizing, the order of the reactivity series, the iron nail in copper sulfate solution, electrolysis of aluminum oxide, the voltages of common batteries and the hydrogen fuel cell were checked a second time against BBC Bitesize (https://www.bbc.co.uk/bitesize/): Redox, rusting and iron (articles/zwt2b7h), Oxidising and reducing agents (guides/z2r44wx), Corrosion of metals (guides/z8kmcj6), Electrolysis (guides/zcsyw6f), Chemical cells and fuel cells (guides/z3fsdxs), The reactivity series of metals (guides/z6c26yc), Displacement reactions (articles/zfy98hv) and Redox, extraction of iron and transition metals (guides/zv7f3k7). The products of a hydrogen fuel cell are also from Fuel Cells of the U.S. Department of Energy (https://www.energy.gov/eere/fuelcells/fuel-cells). The fact after each meaning is from the same pages. Licence: own work
How it works
This oxidation and reduction vocabulary worksheet puts oxidation, reduction, electron, oxidizing agent, reducing agent, corrosion and six more terms beside their meanings in another order. The key is the last page. It has no equations to balance.
Read the full guide
Cells and electrolysis
Set opens on Oxidation and reduction. The second set has electrode, anode, cathode, electrolyte, galvanic cell, half-cell, salt bridge, electrolysis, electroplating, battery, fuel cell and voltage.
Metals and everyday redox
The third set has tarnish, patina, galvanization, sacrificial anode, reactivity series, displacement reaction, smelting, antioxidant, passivation, disproportionation, stainless steel and anodizing.
Ion, cation, anion, catalyst and precipitate are on the chemistry flashcards.
Questions and answers
What does OIL RIG stand for?
Oxidation Is Loss, Reduction Is Gain, of electrons in both cases. A second memory aid says the same: LEO the lion says GER, for loss of electrons is oxidation, gain of electrons is reduction.
Is rusting oxidation or reduction?
Both at once. The iron is oxidized: its atoms give up electrons as the metal turns to oxide. The oxygen is reduced: it takes those electrons up. Rusting is a redox reaction.
Why is the oxidizing agent reduced?
It is named for what it does to its partner. An oxidizing agent oxidizes the other substance by taking electrons from it, and gaining electrons is reduction. So the oxidizing agent is itself reduced.
How do you tell which element is oxidized?
Compare oxidation states before and after the reaction. The one whose number rises was oxidized, and the one whose number falls was reduced. Zinc metal turning into a zinc ion goes from 0 to +2, so it is oxidized.