Topic 9: Redox Reactions

gain of oxygen loss of hydrogen increase in oxidation number loss of electrons

loss of oxygen gain of hydrogen decrease in oxidation number gain of electrons

oxidizing agents oxidize other species + themselves get reduced

reduxing agents reduce other species + themselves get oxidized

ranks elements according to the ease that they undergo oxidation (the more electronegative; swap values)

make strong reducing agents (easily oxidized) -reduce the ions of less reactive metals by displacement reactions

strong oxidizing agents (easily reduced) -oxidize the ions of less reactive non-metals

Redox titrations are used to determine concentrations of solutions by finding the equivalence point when two reactants have reacted stoichiometrically, by transferring electrons from the reducing agent to the oxidizing agent. • reaction between oxidizing agent + reducing agent • electrons are transferred from reducing agent to oxidizing agent examples; 1. analysis of iron with mangate (vii) (color change from deep purple to colorless; MnO4 as oxidizing agent) • iodine-thiosulfate reaction - iodine + oxidizing agent - livreated iodine titrated with sodium thiosulfate using starch as indicator (during titration) - color change; blue to clear

• uses redox titration to determine oxygen content of water (dissolved oxygen) 1- reaction manganese salt with water (reacts with oxygen in basic solution; causes oxidation of Mn(II) ) 2- acidified iodide ions are added and oxidex by Mn(IV to I2 • iodine produed is titrated with sodium thiosulfate to find amount of oxygen used in water

generate electricity from spontaneous redox reaction - convert chemical energy to electrical energy

external source drives non-spontanoes reactions - convert electrical energy to chemical energy

• electrical connecion between 2 half cells allowing ions o flow between half cells • anions flow back throught he salt bridge from the cathode • electrons flow through external circiut from more reactive metal to less reactive metal • prevents build up by charge (movement of ions) salt bridge’ is usually a filter paper soaked in potassium nitrate solution (neither of these ions react with any other ions in the experiment). This ‘salt bridge’ then allows ions to move in both directions equalising any build up of electrical charge in the beakers.

• the more reactive the metal, the more negative is its electrodge potential in the half cell ( undergoes oxidation) • two half cells connected; electrodes; creates potential difference (VOLTAGE)

• positive electrode is the cathode -negative electrode is the anode • anode – > cathode eletron flow • salt bridge • voltmeter • metal solutions + corresponding metal • generate voltage (electrodge potential) • Electrons flow through the external circuit of a voltaic cell from anode to cathode

OXIDATION; • +ve in electrolytic cell • -ve in voltaic cell

REDUCTION: +ve in electolytic cell -ve in voltaic cell

• singular container with an electrolyte solution (molten NaCL for example or aqueous solution) • both electrodes in solution • external power source • ammeter • positive electrode is anode • negative electrode is cathode • no saltbridge • possible external heat source • electrical charge carried by mobile ions in solution; neutral products discharged from each electrode

oxidation at anode reduction at cathode electrons flow from anode to cathode