What is cathode and anode?

Cathode is negative terminal or electrode through which electrons enter a direct current load, such as an electrolytic cell and the positive terminal of a battery or other source of electrical energy through which they return. This terminal corresponds in electrochemistry to the terminal at which reduction occurs. Within a gas discharge tube, electrons travel away from the cathode, but positive ions (current carriers) travel toward the cathode. 

Anode is the terminal or electrode from which electrons leave a system. In a battery or other source of direct current the anode is the negative terminal, but in a passive load it is the positive terminal. For example, in an electron tube electron from the cathode travel across the tube toward the anode, and in an electroplating cell negative ions are deposited at the anode. 

SPM Form 5: Oxidation and Reduction (Checklist)

• Oxidation: A reaction that occurs when a substance gains oxygen.
• Oxidizing agent: The substance that oxidizes other reacting substances in a reaction while it is being reduced.
• Reduction: The reaction that occurs when a substances loses oxygen.
• Reducing agent: The substance that reduces other reacting substances in a reaction in a reaction while it is being oxidized.
• Redox reaction: A chemical reaction in which oxidation and reduction occur simultaneously.
• Metal displacement reaction: A reaction where a more electropositive metal replaces a less electropositive metal from its salt solution. In a metal displacement reaction, a more electropositive metal acts as the reducing agent whereas the ion of the less electropositive metal in the salt solution acts as the oxidizing agent.
• Halogen displacement reaction: A reaction where a more reaction halogen replaces a less reactive halogen from its halide solution. In a halogen displacement reaction, a more reactive halogen acts as the oxidizing agent whereas the halide ion of the less reactive halogen acts as the reducing agent.
• Rusting of iron = the corrosion of ion.  Rusting can be prevented when iron is in contact with a more electropositive metal. Rusting occurs faster when iron is in contact with a less electropositive metal.
• Reactivity series of metals: A list of metal that are arranged according to their reactivity with oxygen. The descending order of reactivity of metal with oxygen is magnesium, zinc, iron, lead and copper.
• Carbon is placed between aluminium and zinc in the reactivity series. Magnesium is placed higher than carbon in the reactivity series. Carbon acted as a reducing agent because the metal oxide was reduced to metal in the presence of carbon.
• Hydrogen is placed between zinc and iron in the reactivity series. Hydrogen gas acted as a reducing agent because the metal oxide was reduced to metal in the presence of hydrogen gas.
• In an electrolytic cell, oxidation takes place at the anode whereas reduction takes place at the cathode.
• In a chemical cell, oxidation takes place at the negative terminal (anode) whereas reduction takes place at the positive terminal (cathode).