8. Redox Reactions

Question 1

Oxidation

Answer 1

Addition of oxygen
Removal of hydrogen
Loss of electrons
Increase in oxidation number/ oxidation state

Question 2

Reduction

Answer 2

Removal of oxygen
Gain of hydrogen
Gain of electrons
Decreases in oxidation number/ oxidation state

Question 3

Oxidation Rule for uncombined element

Answer 3

Any uncombined element has oxidation state O

Ex.
CL2= O
Na= O
N2= O

Question 4

Oxidation Rule for simple ions

Answer 4

The oxidation state of simple ions is the same as their valencies.

Ex.
Mg2+ —-> +2

Question 5

Oxidation rule for all the elements in a compound

Answer 5

The sum of the oxidation states of all the elements in a compound is equal to O.

Question 6

Oxidation rule for all the elements in a polyatomic ion

Answer 6

The sum of the oxidation states of the elements in a polyatomic ion is equal to the charge of the ion.

Question 7

The oxidation rule of hydrogen

Answer 7

The oxidation state of hydrogen is always +1 except metal hydrides (ex. NaH) where it is -1.

Question 8

The oxidation rule of oxygen

Answer 8

The oxidation state of oxygen is always -2.

Question 9

Function of cell

Answer 9

To convert chemical energy to electric electricity

Question 10

Function of salt bridge in voltaic cell

Answer 10

1) The salt bridge helps to maintain the neutrality of the solution.

2) Movement of ions (cation to cathode and anion to anode) takes place via the salt bridge.

Question 11

What salts does a salt bridge contain?

Answer 11

A salt bridge will contain metal salts as they are higher on the reactivity series and they would not interfere with the movement of ions.

Ex. of salts which can be used:
KNO3 (potassium nitrate)
NaNO3 (Sodium nitrate)

Question 12

Why do we generally use nitrates for salt bridge salts?

Answer 12

We generally use nitrates as they are soluble in water

Question 13

Why will anode have a negative charge in a voltaic cell?

Answer 13

Electrons will be accumulated in the anode as it is loosing electrons, thus the anode will have a negative charge.

Question 14

Where does oxidation take place?

Answer 14

Anode
(An Ox)

Question 15

Where does reduction take place?

Answer 15

Cathode
(Red Cat)

Question 16

Electroplating

Answer 16

Electroplating is a process that uses electrolysis to coat an object with a thin layer of metal.

Question 17

What will be the cathode/ anode in electroplating?

Answer 17

The object which is to be plated/ coated will be the cathode.

The metal which you want to use to plate will be the anode.

Question 18

Active electrodes

Answer 18

Made up of metals which loose electrons. Active electrode should be taken at anode as there is loss of electrons in anode which favors metals.

Question 19

Factors affecting Voltaic cell

Answer 19

Electrode Material

Electrolyte Concentration

Temperature

Surface Area of Electrodes

Question 20

Material of anode and cathode in a voltaic cell

Answer 20

Zinc- as the anode

Copper- as the cathode

Question 21

How does electrode material affect a voltaic cell?

Answer 21

The more easily a metal loses electrons, the higher the voltage

Question 22

How does concentration of the electrolyte affect a voltaic cell?

Answer 22

Increased ion concentration in the electrolyte enhances the rate of chemical reactions, leading to higher voltage

Question 23

How does the temperature affect a voltaic cell?

Answer 23

Higher temperature leads to a lower voltage due to higher internal resistance

Question 24

How does the surface area of the electrodes affect a voltaic cell?

Answer 24

Larger surface area: Greater contact between electrodes and electrolyte, faster
reactions, higher voltage.