Electrochemistry

Question 1

What is Electrochemistry?

Answer 1

The study of the conversion of electrical energy and chemical energy

Question 2

What is an Electrolytic Cell?

Answer 2

A type of cell where the current is used to induce a chemical reaction to produce useful chemical

Happens through the procces of electrolysis

Question 3

What is Electrolysis?

Answer 3

The chemical decomposition of a compound(electrolyte) when electricity is passed through it causing a chemical change

Question 4

Describe the process of Electrolysis

Answer 4

The electrolysis process requires an electrolyte, two electrodes, the cathode and the anode ( the electrodes used do not react with the electrolytes), and a power source (battery).

Question 5

What is an Anode

Answer 5

The positively charged electrode where oxidation takes place

Question 6

What is a Cathode?

Answer 6

The negatively charged electrode where reduction occurs

Question 7

What happens in the cell?

Answer 7

-The positive terminal connects to the anode and the negative terminal to the cathode
-The electrolytes dissociate into cations Na⁺
and anions Cl⁻
.-Under the influence of the electric field, cations migrate toward the cathode and anions migrate toward the anode
-At the cathode, reduction occurs as cations gain electrons; Na⁺ + e⁻ → Na
-At anode, oxidation occurs as anions lose electrons; 2Cl⁻ → Cl₂ + 2e-
-The reaction at both electrodes combine to give the overall chemical reaction ;
2NaCl → 2Na + Cl

Question 8

How does electrolysis occur in and aqueous salt solution?

Answer 8

Reduction occurs in ion with less
negative/more positive electropotential and oxidation occurs in ion with less
positive / more negative electrode potential.

Question 9

What is Over Voltage?

Answer 9

The
increment above the expected voltage

Cl⁻ (1.36v)
OH⁻ (0.82v) with an overvoltage of 0.6V (≈1.4V)
Because of the overvoltage of 0.6v makes the potential of OH⁻ to be slightly above that of Cl₂ hence Cl₂ is formed at the anode

Question 10

How does nature of the electrolyte effect electrolysis?

Question 11

How does the relative concentration of ions in a solution effect electrolysis?

Question 12

How does nature of an electrode effect electrolysis

Question 13

How does position in electrochemical series affect electrolysis

Question 14

Know graph of electrolyte cells

Question 15

What is Electroplating

Answer 15

When a thin layer of metal, like gold or silver, is applied to a metal object using
electrolysis.

The object to be coated is the cathode and the metal ion source is the anode.
When an electric current passes through, the metal ions are deposited onto the object

Question 16

What is Electrorefining

Answer 16

A process that uses electrolysis to purify metals like copper, silver and gold.

In this process, impure metal is placed as the anode in an electrolyte solution and a
strip of pure metal is the cathode

Question 17

How is electrolysis used in extracting metals

Answer 17

Electrolysis is used to separate metal ions from solution or molten substance and deposit them as pure metal at the electrodes

. Its particularly useful for
extracting metals that can’t be obtained through smelting or reduction, like magnesium
and aluminium.

Question 18

What is Galvanic (Voltaic) Cell?

Answer 18

An electrochemical cell that generates electrical energy from a spontaneous redox reaction.
-It consists of two half-cells, each
containing an electrode and electrolyte, connected by a salt bridge to allow the
flow of ions

Question 19

Electrodes in Galvanic Cells

Answer 19

-Anode: The negative electrode where oxidation occur (loss of
electrons).
-Cathode: The positive electrode where reduction occur (gain of
electrons).

Question 20

What are electrolytes in Galvanic Cell?

Answer 20

-Solutions that contain ions to conduct electricity
-Each half-cell has an electrolyte that participates in the redox reaction

Question 21

What is a Salt Bridge?

Answer 21

A tube or membrane filled with concentrated salt solution

-It prevents direct mixing of two electrolytes
-Maintains electrical neutrality by allowing the movement of ions
between the two half cells

Question 22

What is an External Circuit?

Answer 22

What is a wire that connects the electrodes, allowing flow from the anode to the cathode

Question 23

What is the working principle of a Galvanic Cell?

Answer 23

1.At the Anode, oxidation occurs: metal atoms lose electrons and become ions
Example: Zn → Zn²⁺ + 2e⁻
2. The released electrons flow through the external circuit to the cathode.
3. At the cathode, reduction occurs: ions gain electrons and are reduced
Example: Cu²⁺ + 2e⁻ → Cu
4. The salt bridge maintains the charge balance by allowing anions to flow
toward the anode and cations(in the salt bridge) to flow toward the cathode
5. The cell produces a voltage( cell potential) that can be measured using a
voltameter
6. The overall cell reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu

Question 24

What is a Metal-Metal ion half-cell

Answer 24

The half-cell is made of a metal dipped into the solution if a metal ion

E.g, Zn/Zn²⁺ or Cu/Cu²⁺

Question 25

What is a Non-metal/Non-metal ion half-cell

Answer 25

A half-cell made of an element in contact with its ions in solution, using an inert electrode like platinum ## Footnote E.g., H₂(g)/ H⁺(aq) or Cl₂/Cl

Question 26

What is a Ion-ion half-cell?

Answer 26

A half-cell made of an inert electrode (platinum) dipped in a solution containing ions of same metal but different oxidation states. ## Footnote E.g., Fe²⁺/Fe³⁺ or Cu⁺/Cu²⁺

Question 27

What is a Metal-Metal salt half-cell?

Answer 27

A half-cell made of a metal electrode dipped in sparingly soluble salt solution and its ions ## Footnote E.g., Ag/AgCl(s)/Cl-(aq)

Question 28

What is Cell Notation

Answer 28

A way of describing the components of a voltaic cell, including the oxidation and reduction half-reactions ## Footnote The cell notation for Zn/Cu²⁺ cell is written as; Zn(s)/Zn²⁺ (aq)//Cu²⁺ (aq)/Cu(s)

Question 29

Note when writing Cell Notation

Answer 29

1. The components of the anode compartment are written first before the cathode compartment. 2. A single vertical line represents phase boundary 3. A comma is used when the components are in the same phase 4. A double vertical line indicates the separated half-cells ## Footnote  Often times we specify the concentration of dissolved components e.g, if the concentration of Zn²⁺ and Cu²⁺ is 1M. the cell notation is written as Zn(s)/Zn²⁺(aq) (1M)//Cu²⁺(aq)(1M)/Cu(s)

Question 30

What is Electrode (Reduction) Potential (E)

Answer 30

The measure of how a substance is reduced

Question 31

What is Standard electrode potential (E○cell)

Answer 31

The voltage measured under standard conditions ## Footnote E○cell = E(cathode) - E(anode) the more positive (or less negative) an electrode potential is, the more likely it is for that specie to undergo reduction

Question 32

What is standard conditions for electrode potential

Answer 32

-Concentration of ions at 1mol/dm3 -Temperature at 25 or 298K ℃ -Any gas involved should be at a pressure of 1atm

Question 33

What is Non-Standard Cell Potential (Ecell)

Answer 33

-Concentration is less than or greater than 1mol/dm3 -Temperature below or above 25℃ -Pressure not equal to 1atm

Question 34

What happens to Electrode Potential When Increasing concentration of species on the left?

Answer 34

If the concentration of the species on the left is increased, the position of the equilibrium will shift to the right. This means that the species on the left gets more easily reduced and the E value becomes more positive (or less negative)

Question 35

What happens to Electrode Potential When Increasing concentration of species on the Right?

Answer 35

If the concentration of the species on the right is increased, the position of equilibrium will shift to the left. This means that the species on the left will be less easily reduced and the E value becomes less positive (or more negative).

Question 36

Know how Nernst Equation relates SCP and non-SCP

Question 37

What is Rusting

Answer 37

The process by which iron corrode in the presence of oxygen and water forming a reddish-brown substance called rust.

Question 38

What are the conditions for Rusting

Answer 38

-Moisture/oxygen must be present -iron rusts more quickly at low pH{ high H+ } -iron rusts more quickly in contact with ionic solutions -it rusts more quickly in contact with less active metal (Copper) -the loss of iron and depositing of rust often occur at different places on same object Chemical Process of Rusting Rusting occurs in two main stages:  oxidation of iron: iron reacts with water to form iron(II)ions and releases electrons Fe(s) → Fe2+ (aq) + 2e-  reduction of oxygen: the electrons released from iron are taken up by oxygen and water, forming hydroxide ions O2(g) + 4e- + 4H2O(l) → 4OH- (aq)  formation of rust: the iron (II)ions and hydroxide react to form iron(II)hydroxide Fe2+ (aq) + 2OH- (aq) → Fe(OH)2(s) The iron(II)hydroxide is further oxidized in the presence of oxygen to form hydrated iron(III) oxide (rust). 4Fe(OH)2(s) + O2(g) + 2H2O(l) → Fe2O3.nH2O(s) FUEL CELLS AND BATTERIES Fuel cells are devices that convert chemical energy directly into electrical energy through redox reaction. It uses hydrogen and oxygen as reactants to produce electricity, water and heat. Components of a fuel Cell  Anode: hydrogen gas is supplied at the anode and oxidation occurs at anode

Question 39

Know the chemical process of rusting

Question 40

What is Fuel Cell?

Answer 40

Devices that convert chemical energy directly into electrical energy through redox reaction.

Question 41

What are the components of a Components of a fuel Cell?

Answer 41

-Anode: hydrogen gas is supplied at the anode and oxidation occurs at anode -Cathode: oxygen gas is supplied to the cathode and reduction occurs at the cathode -Electrolyte: allows the movement of ions between the anode and cathode -External Circuit: electrons flow through the circuit generating electricity

Question 42

What is a battery?

Answer 42

A battery is a device that converts stored chemical energy into electrical energy

Question 43

What are Primary Batteries

Answer 43

-Single use, non rechargeable batteries. -The electrochemical reactions that take place in these cells are irreversible in nature ## Footnote The cell stops producing electric current once the reactants are completely depleted.

Question 44

What are examples of primary Batteries

Answer 44

1. Alkaline battery -zinc anode - cathode is an inactive graphite

Question 45

What is Faraday's Law of Electrolysis

Answer 45

That the quantity of products liberated, dissolved or discharged at the electrode during electrolysis depends on: -The magnitude of steady current -The time flow of steady current -The ionic charge of liberated elements species

Question 46

What is the First Law of Faraday?

Answer 46

The mass of any substance liberated at or dissolved from an electrode during electrolysis is directly proportional to the quantity of electricity Q(in Coulombs) passing through the electrolyte ## Footnote m ∝ Q Q= I×t m∝ I×t m = Z×I×t

Question 47

What is the Second Law of Faraday?

Answer 47

States that the masses of different ions liberated at electrodes when the same amount of electricity is passed through different electrolytes is directly proportional to their chemical equivalents ## Footnote M₁ /Z₁ = M₂/Z₂

Question 48

What is a Faraday?

Answer 48

The quantity of electricity 1 faraday is quantity of electric charge carried by 1mole of electrons ## Footnote 1F = 96500C

Question 49

Know how to calculate amount of substance produced during electrolysis: