8. Redox Reactions Flashcards
Oxidation
Addition of oxygen
Removal of hydrogen
Loss of electrons
Increase in oxidation number/ oxidation state
Reduction
Removal of oxygen
Gain of hydrogen
Gain of electrons
Decreases in oxidation number/ oxidation state
Oxidation Rule for uncombined element
Any uncombined element has oxidation state O
Ex.
CL2= O
Na= O
N2= O
Oxidation Rule for simple ions
The oxidation state of simple ions is the same as their valencies.
Ex.
Mg2+ —-> +2
Oxidation rule for all the elements in a compound
The sum of the oxidation states of all the elements in a compound is equal to O.
Oxidation rule for all the elements in a polyatomic ion
The sum of the oxidation states of the elements in a polyatomic ion is equal to the charge of the ion.
The oxidation rule of hydrogen
The oxidation state of hydrogen is always +1 except metal hydrides (ex. NaH) where it is -1.
The oxidation rule of oxygen
The oxidation state of oxygen is always -2.
Function of cell
To convert chemical energy to electric electricity
Function of salt bridge in voltaic cell
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.
What salts does a salt bridge contain?
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)
Why do we generally use nitrates for salt bridge salts?
We generally use nitrates as they are soluble in water
Why will anode have a negative charge in a voltaic cell?
Electrons will be accumulated in the anode as it is loosing electrons, thus the anode will have a negative charge.
Where does oxidation take place?
Anode
(An Ox)
Where does reduction take place?
Cathode
(Red Cat)
Electroplating
Electroplating is a process that uses electrolysis to coat an object with a thin layer of metal.
What will be the cathode/ anode in electroplating?
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.
Active electrodes
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.
Factors affecting Voltaic cell
Electrode Material
Electrolyte Concentration
Temperature
Surface Area of Electrodes
Material of anode and cathode in a voltaic cell
Zinc- as the anode
Copper- as the cathode
How does electrode material affect a voltaic cell?
The more easily a metal loses electrons, the higher the voltage
How does concentration of the electrolyte affect a voltaic cell?
Increased ion concentration in the electrolyte enhances the rate of chemical reactions, leading to higher voltage
How does the temperature affect a voltaic cell?
Higher temperature leads to a lower voltage due to higher internal resistance
How does the surface area of the electrodes affect a voltaic cell?
Larger surface area: Greater contact between electrodes and electrolyte, faster
reactions, higher voltage.
