Topic 9: Redox Reactions

Question 1

Oxidation

Answer 1

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

Question 2

Reduction

Answer 2

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

Question 3

oxidizing agents

Answer 3

oxidizing agents oxidize other species + themselves get reduced

Question 4

reducing agents

Answer 4

reduxing agents reduce other species + themselves get oxidized

Question 5

the activity series

Answer 5

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

Question 6

reactive metals

Answer 6

make strong reducing agents (easily oxidized)

-reduce the ions of less reactive metals by displacement reactions

Question 7

reactive non-metals

Answer 7

strong oxidizing agents (easily reduced)

-oxidize the ions of less reactive non-metals

Question 8

Redox titrations

Answer 8

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)

2. iodine-thiosulfate reaction
   - iodine + oxidizing agent
   - livreated iodine titrated with sodium thiosulfate using starch as indicator (during titration)
   - color change; blue to clear

Question 9

Winkler Method

Answer 9

• 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

3. iodine produed is titrated with sodium thiosulfate to find amount of oxygen used in water

Question 10

voltaic cell

Answer 10

generate electricity from spontaneous redox reaction

- convert chemical energy to electrical energy

Question 11

electrolytic cells

Answer 11

external source drives non-spontanoes reactions

- convert electrical energy to chemical energy

Question 12

why does a voltaic cell need a salt bridge

Answer 12

• 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.

Question 13

what is electrode potential

Answer 13

• 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)

Question 14

features of voltaic cell

Answer 14

• 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

Question 15

anodE

Answer 15

OXIDATION;

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

Question 16

cathode

Answer 16

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

Question 17

features of electolytic cell

Answer 17

• 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

Question 18

in all cells..

Answer 18

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