Key terms: Redox Equilibrium

Use this glossary to fix the exact meaning of each term this chapter examines. Learn every definition with its electron direction where relevant, because the marking scheme rewards precise wording, not a rough idea. The English term is given first; where it helps, the Malay and Chinese term follow in brackets.

Oxidation and reduction

• Oxidation (pengoksidaan / 氧化). The loss of electrons by a species; also the gain of oxygen or the loss of hydrogen. Its oxidation number increases.
• Reduction (penurunan / 还原). The gain of electrons by a species; also the loss of oxygen or the gain of hydrogen. Its oxidation number decreases.
• Redox reaction (tindak balas redoks / 氧化还原反应). A reaction in which oxidation and reduction occur together, because electrons lost by one species are gained by another.
• Oxidising agent (agen pengoksidaan / 氧化剂). The substance that causes oxidation by accepting electrons; it is itself reduced in the reaction.
• Reducing agent (agen penurunan / 还原剂). The substance that causes reduction by donating electrons; it is itself oxidised in the reaction.
• OIL RIG. A memory aid: Oxidation Is Loss, Reduction Is Gain, of electrons.

Oxidation number

• Oxidation number (nombor pengoksidaan / 氧化数). A signed value assigned to an atom that shows how many electrons it has effectively gained or lost. An uncombined element is 0.
• Stock nomenclature. Naming a compound using a Roman numeral to show the oxidation number of an element, e.g. iron(II) for +2 and iron(III) for +3.
• Half-equation (setengah persamaan / 半反应式). An ionic equation that shows either the loss of electrons (oxidation) or the gain of electrons (reduction) at one electrode or for one species.

Displacement and reactivity

• Displacement reaction (tindak balas penyesaran / 置换反应). A reaction in which a more reactive element takes the place of a less reactive one in a compound; it is a redox reaction because electrons transfer.
• Reactivity series (siri kereaktifan / 活性顺序). A list of metals arranged in order of how readily they lose electrons, from the most reactive to the least reactive.
• Electrochemical series (siri elektrokimia / 电化学序). An ordered list of ions used to predict which ion is discharged first during electrolysis; ions of less reactive elements are discharged more readily.

Electrolysis

• Electrolysis (elektrolisis / 电解). The decomposition of an electrolyte into its elements using a direct electric current.
• Electrolyte (elektrolit / 电解质). A substance that conducts electricity when molten or in aqueous solution and is decomposed by it, because it contains freely moving ions.
• Electrode (elektrod / 电极). A conductor through which current enters or leaves an electrolyte.
• Anode (anod / 阳极). The positive electrode in electrolysis, where anions are oxidised (lose electrons).
• Cathode (katod / 阴极). The negative electrode in electrolysis, where cations are reduced (gain electrons).
• Cation (kation / 阳离子). A positively charged ion that moves to the cathode.
• Anion (anion / 阴离子). A negatively charged ion that moves to the anode.
• Selective discharge (penyahcasan terpilih / 选择性放电). The process by which, when more than one type of ion could be discharged, one is discharged in preference according to position in the electrochemical series, concentration and electrode type.
• Inert electrode (elektrod lengai / 惰性电极). An electrode such as carbon or platinum that does not take part in the electrode reaction.
• Active electrode (elektrod aktif / 活性电极). An electrode such as copper that itself reacts, for example dissolving at the anode.
• Electroplating (penyaduran / 电镀). Coating an object with a thin layer of metal by making it the cathode in a suitable electrolyte.

Cells and corrosion

• Voltaic cell (sel voltan / 伏打电池). A cell that converts chemical energy to electrical energy using two metals of different reactivity in an electrolyte; the more reactive metal is the negative terminal.

• Electrolytic cell (sel elektrolisis / 电解电池). A cell that uses electrical energy to drive a non-spontaneous chemical change.

• Salt bridge (jambatan garam / 盐桥). A connection containing an electrolyte that completes the circuit between two half-cells while allowing ions to move.

• Rusting (pengaratan / 生锈). The oxidation of iron to hydrated iron(III) oxide, which requires both water and oxygen to occur.

• Sacrificial protection (perlindungan korban / 牺牲保护). Protecting iron by attaching a more reactive metal such as zinc or magnesium, which is oxidised in place of the iron.

• Galvanising (penggalvanian / 镀锌). Coating iron or steel with zinc, which acts as both a barrier and, if scratched, a sacrificial metal.

• Electron transfer at a distance (pemindahan elektron pada suatu jarak / 远距离电子转移). A set-up in which the oxidising and reducing halves are separated but joined by a wire and salt bridge, so the electron flow of a displacement can be detected on a galvanometer.

• Corrosion (kakisan / 腐蚀). The gradual oxidation of a metal by substances in its surroundings; rusting is the corrosion of iron.

Extraction

• Metal extraction (pengekstrakan logam / 金属提取). Obtaining a metal from its ore; the method depends on the metal’s position in the reactivity series, electrolysis for very reactive metals, carbon reduction for moderately reactive ones.
• Carbon reduction (penurunan karbon / 碳还原). Extracting a metal by heating its oxide with carbon, which removes the oxygen; it works only for metals less reactive than carbon.
• Thermite reaction (tindak balas termit / 铝热反应). A displacement in which aluminium reduces iron(III) oxide to iron, releasing a great deal of heat, showing aluminium is above iron in the reactivity series.
• Purification of copper (penulenan kuprum / 铜的提纯). An electrolysis using an impure copper anode and a pure copper cathode, so pure copper transfers to the cathode while impurities collect below the anode.

Using the glossary

Recite each definition until you can give it without the electron direction going missing, because that is the phrase the examiner is looking for. A one-to-one teacher can check that your wording matches the standard for SPM Chemistry. Then test yourself against the practice questions and the worked examples, and return to any term whose definition you could not give cleanly.