12: Redox And Electrochemistry

Question 1

What is electrochemistry

Answer 1

Is the study of relationship btn chemical rx’s and electricity.
Also dealing with redox reactions.

Question 2

LEO and GER ?

Answer 2

Losing electrons = oxidation (LEO)

Gaining electrons = reduction (GER)

Question 3

Important facts about ox states

Answer 3

• The atoms in any compound can be assigned ox numbers.
• For any compound the total number of electrons given equals number of electrons gained. Thus, the ox. of all the atoms in a neutral compound add up to zero

Question 4

When do we assign ox states to atoms

Answer 4

When they are not in their elemental form

Ex: H2, O2 etc, only in compounds

Question 5

Elements in which ox state varies

Answer 5

• Oxygen always has ox state of -2, EXCEPT in hrogen peroxide, H2O2, where it is -1
• when hydrogen is with a nonmetal= +1, but when with a metal = -1

Question 6

What is a half rx

Answer 6

A rx showing just reduction only or ox only

Question 7

Examples of powerful oxidizing and reducing agents

Answer 7

• Oxygen and Fluorine are powerful oxidizing agent, due to high electronegativity they can easily gain electrons, making others undergo oxidation (lose electrons)
• and also the active metals (period II) make strong reducing agents, due to that they are easily loose electrons to be oxidised hence reducing others.

Question 8

What is an electrochemical cell or voltaic or galvanic cell

Answer 8

Is a device used to produce electricity from spontaneous redox rx’s.

Question 9

What is the function of salt bridge

Answer 9

It neutralizes any excess charge builup

- as positive charge accumulates in the oxidation vessel, anions flow into it from the salt bridge.

Question 10

What is electrolysis

Answer 10

A process by which electrical energy is put into a non spontaneous redox rx to force it to occur.
Electrical energy is converted to chemical energy

Question 11

What is activity series ?

Answer 11

Is a qualitative series that compares the reactivity of the various metals w/ water or acids

Question 12

Examples of common redox reaction

Answer 12

• rusting: ex of oxygen with metals to form rust.
  Silver, gold cannot rust bcs they are low on the reactivity series of metals w/ water or acids.
• Dissolving: acids dissolve metals.
  But metals that are low on reactivity series will resist being oxidised by hydrogen just as with O2. The rx produces metal ions w/ H2 gas.
• Nitric acid dissociation: unlike the other five strong acids, Nitric acid does not dissolve a metal in the same type of rx.

Question 13

Why is Dissolving a faster process than rusting

Answer 13

02 is a better oxidizing agent than a strong acid, but there are very few molecules in contact with a metal surface due to diffuse nature of a gas. However, in liquid, a lot hydrogen ions will come into contact w/ the metal.

Question 14

Why does Nitric acid not dissociate a metal in the same type of rx as other five strong acids

Answer 14

This is bcs the nitrate ion is a strong oxidizing agent than the hydrogen ion present in all strong acids.
The rx produces nitrogen dioxide gas, metal ions and water