Electrochemistry Flashcards
What is Electrochemistry?
The study of the conversion of electrical energy and chemical energy
What is an Electrolytic Cell?
A type of cell where the current is used to induce a chemical reaction to produce useful chemical
Happens through the procces of electrolysis
What is Electrolysis?
The chemical decomposition of a compound(electrolyte) when electricity is passed through it causing a chemical change
Describe the process of Electrolysis
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).
What is an Anode
The positively charged electrode where oxidation takes place
What is a Cathode?
The negatively charged electrode where reduction occurs
What happens in the cell?
-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
How does electrolysis occur in and aqueous salt solution?
Reduction occurs in ion with less
negative/more positive electropotential and oxidation occurs in ion with less
positive / more negative electrode potential.
What is Over Voltage?
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
How does nature of the electrolyte effect electrolysis?
How does the relative concentration of ions in a solution effect electrolysis?
How does nature of an electrode effect electrolysis
How does position in electrochemical series affect electrolysis
Know graph of electrolyte cells
What is Electroplating
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
What is Electrorefining
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
How is electrolysis used in extracting metals
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.
What is Galvanic (Voltaic) Cell?
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
Electrodes in Galvanic Cells
-Anode: The negative electrode where oxidation occur (loss of
electrons).
-Cathode: The positive electrode where reduction occur (gain of
electrons).
What are electrolytes in Galvanic Cell?
-Solutions that contain ions to conduct electricity
-Each half-cell has an electrolyte that participates in the redox reaction
What is a Salt Bridge?
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
What is an External Circuit?
What is a wire that connects the electrodes, allowing flow from the anode to the cathode
What is the working principle of a Galvanic Cell?
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
What is a Metal-Metal ion half-cell
The half-cell is made of a metal dipped into the solution if a metal ion
E.g, Zn/Zn²⁺ or Cu/Cu²⁺
What is a Non-metal/Non-metal ion half-cell
A half-cell made of an element in contact with its ions in solution, using an inert electrode like platinum
E.g., H₂(g)/ H⁺(aq) or Cl₂/Cl
What is a Ion-ion half-cell?
A half-cell made of an inert electrode (platinum) dipped in a solution containing ions of same metal but different oxidation states.
E.g., Fe²⁺/Fe³⁺ or Cu⁺/Cu²⁺
What is a Metal-Metal salt half-cell?
A half-cell made of a metal electrode dipped in sparingly soluble salt solution and its ions
E.g., Ag/AgCl(s)/Cl-(aq)
What is Cell Notation
A way of describing the components of a voltaic cell, including the oxidation
and reduction half-reactions
The cell notation for Zn/Cu²⁺ cell is written as;
Zn(s)/Zn²⁺ (aq)//Cu²⁺ (aq)/Cu(s)
Note when writing Cell Notation
- The components of the anode compartment are written first before the
cathode compartment. - A single vertical line represents phase boundary
- A comma is used when the components are in the same phase
- A double vertical line indicates the separated half-cells
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)
What is Electrode (Reduction) Potential (E)
The measure of how a substance is reduced
What is Standard electrode potential (E○cell)
The voltage measured under
standard conditions
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
What is standard conditions for electrode potential
-Concentration of ions at 1mol/dm3
-Temperature at 25 or 298K ℃
-Any gas involved should be at a pressure of 1atm
What is Non-Standard Cell Potential (Ecell)
-Concentration is less than or greater than 1mol/dm3
-Temperature below or above 25℃
-Pressure not equal to 1atm
What happens to Electrode Potential When Increasing concentration of species on the left?
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)
What happens to Electrode Potential When Increasing concentration of species on the Right?
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).
Know how Nernst Equation relates SCP and non-SCP
What is Rusting
The process by which iron corrode in the
presence of oxygen and water forming a reddish-brown substance called rust.
What are the conditions for Rusting
-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
Know the chemical process of rusting
What is Fuel Cell?
Devices that convert chemical energy
directly into electrical energy through redox reaction.
What are the components of a Components of a fuel Cell?
-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
What is a battery?
A battery is a device that converts stored chemical energy into electrical energy
What are Primary Batteries
-Single use, non rechargeable batteries.
-The electrochemical reactions that take place in these cells are irreversible in nature
The cell stops producing electric current once the reactants are completely depleted.
What are examples of primary Batteries
- Alkaline battery
-zinc anode
- cathode is an
inactive graphite
What is Faraday’s Law of Electrolysis
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
What is the First Law of Faraday?
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
m ∝ Q
Q= I×t
m∝ I×t
m = Z×I×t
What is the Second Law of Faraday?
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
M₁ /Z₁ = M₂/Z₂
What is a Faraday?
The quantity of electricity
1 faraday is quantity of electric charge carried by 1mole of electrons
1F = 96500C
Know how to calculate amount of substance produced during
electrolysis:
