Chemistry - Redox reactions ✅

Including: redox reactions, oxidation states, Electrochemical cells, Galvanic cells, Standard electrode potential, and Electrolytic cells

reactions that can be modelled as redox reactions

single replacement reactions, combustion, corrosion, decomposition, combination and electrochemical processes

what do redox reactions involve

oxidation of one substance and reduction of another substance

What reactant in a reaction will be reduced

reactant with the most positive E0 value

What reactant in a reaction will be the reducing agent

reactant with the most negative E0 value

What reactant in a reaction will be oxidised

Reactant with the most negative E0 value

What reactant in a reaction will be the oxidising agent

reactant with the most positive E0 value

What does O.I.L. stand for

Oxidation is lost (loses electrons)

What does R.I.G. stand for

Reduction is gained (gains electrons)

In an oxidation reaction, what side are the e- on

e- on product side of equation

In a reduction reaction, what side are the e- on

e- on reactant side of equation

What is the reduced agent in this reaction: Zn_(s) + 2H⁺_(aq) → Zn²⁺_(aq) + H_2(g)

Zn as electrons are gained

What is the oxidised agent in this reaction: Zn_(s) + 2H⁺_(aq) → Zn²⁺_(aq) + H_2(g)

H as electrons are lost

what is a reducing agent

a substance which gives e- to the other species and is oxidised

What is a oxidising agent

a substance which takes e- from the other species and is reduced

When are oxidation states used to determine redox reaction half equations

In an equation involves more than two chemical species

What can oxidation states be assigned to

atomic species or to individual atoms within a molecular species

What does an oxidation state/number represent

The charge that an atom would have if it was an ion, shows the number of electrons gained or lost by an atom

What is the oxidation state of a free element (e.g. Na, P, S)

zero

What is the oxidation state of a simple ion (e.g. Mg²⁺, N^3-)

the charge on the ion

What is the oxidation state of main group metals

the charge on their ion

What is the oxidation state of Hydrogen and exceptions

+1 (except of metal hydrides, oxidation state is -1)

What is the oxidation state of oxygen and exceptions

-2 (except in compounds with fluorine, oxygen is positive, in peroxides, oxidation state is -1)

What is the oxidation state of halogens and exceptions

-1 (except in compounds with oxygen or another halogen above them in group 17)

what does the sum of oxidation numbers of all atoms in a neutral compound (e.g. CO₂) equal to

zero

What does the sum of oxidation numbers of all atoms in a polyatomic ion (e.g. SO₄^2-) equal to

The charge on the ion

Which element is assigned the negative oxidation state

the most electronegative element

How can the ability for an atom to lose/gain electrons be predicted

the atom’s position in the periodic table

What properties can be used to explain an atom’s ability to lose or gain electrons

valence electrons, consideration of energy and the overall stability of the atom

What conditions are needed to show redox reactions as half equations

acidic conditions

How can redox reactions be represented

balanced half-equations

What does a galvanic cell do

converts chemical potential energy to electrical energy and spontaneous reactions occur

What is an anode in a galvanic cell

The electrode where oxidation occurs and negatively charged

What are half-cells in a galvanic cell

an electrochemical cell, where either oxidation or reduction occurs

What is an cathode in a galvanic cell

The electrode where reduction occurs and is positively charged

What is the electron movement in a galvanic cell

from anode to cathode

what do salt bridges contain

ions that are free to move so that they can balance charges formed in the two half-cell compartments

What is the flow of molecules in a salt bridge

Cations move towards the cathode and anions toward the anode

EMF formula

EMF (E0 cell) = E0 reduction – E0 oxidation

which side (left or right) is the anode and the charge

left, negative charge

which side (left or right) is the cathode and the charge

right, positive charge

What is a fuel cell

constant supply of reactants, inert electrodes which do not take part in any of the reactions, products are gaseous, liquid or aqueous, produces a current for as long as it has reactants

What do galvanic cells generate

an electrical potential difference

Another term for galvanic cell

voltaic cell

what is a electrochemical cell

a device in which chemical energy is converted into electrical energy

What is a galvanic cell

a type of electrochemical cell in which chemical energy is converted into electrical energy

what would happen if there was no salt bridge in a galvanic cell

each half cell would have a build up of charge taking place, accumulation of charge would stop the reaction very quickly

Other terms for potential difference

electromotive force or voltage

Standard conditions for potential differences

Pressure of 100kPa, Solution concentrations of 1 molL^-1, Temperature of 25°C

what is the strongest reducing agent in a reaction

equation with the most negative E0 value

what is the strongest oxidising agent in a reaction

equation with the most positive E0 value

Where does oxidation occur in a galvanic cell

the negative electrode (anode)

Where does reduction occur in a galvanic cell

the positive electrode (cathode)

What components are required to make a voltaic cell

two half-cells connected by a salt bridge

In electrochemical cells, what is the movement of electrons

from anode (oxidation reaction) to cathode (reduction reaction)

where is the positive electrode (right or left)

right

where is the negative electrode (right or left)

left

what can cell potential values (at standard conditions) be used for

compare cells constructed from different materials

As half equations’ E0 becomes more negative, what does this mean for strength of the agent

will be a stronger reducing agent as E0 values becomes more negative

As half equations’ E0 becomes more positive, what does this mean for strength of the agent

will be a stronger oxidising agent as E0 values becomes more positive

When is a reaction spontaneous

What the E0 value is a positive number (red-ox)

What doe electrochemical cells consist of

oxidation and reduction half-reactions connected via an external circuit

Two types of electrochemical cells

Galvanic and electrolytic

difference between galvanic and electrolytic cells

Galvanic cells produce energy through spontaneous reactions, electrolytic cells produce energy through non-spontaneous reactions

what do electrolytic cells create

convert electrical energy into chemical energy

5 parts of a electrolytic cell

electrolyte, anode, cathode, porous barrier, voltage

what is required for an electrolytic cell to produce a reaction

an external electrical potential difference

two scales of electrolytic cells

small-scale and industrial situations

two examples of electrolytic cells

metal plating and the purification of copper

Porous barrier

separates the products whenthe reaction takes place in a single container

why must an ionic compound be molten (liquid) in electrolysis

a solid ionic compound can not conduct electricity

How many reactants does molten NaCl provide

2

what is electrolysis

a process that produces a non-spontaneous redox reaction by the passage of electrical energy from a power supply through a conducting liquid

Which electrodes are used in electrolysis of molten salt and why

platinum metal or graphite as they allow electron the pass to and from the power supply, and as they are inert they do not react

disadvantage of using a molten electrode

the process requires much more energy

Why are aqueous solutions of salts often used instead of molten salts

it is impractical to produce the high temperatures that are required for the electrolysis of molten salts

what is present in aqueous electrolysis as another reactant

water

what are the reactants in electrolysis of of sodium chloride solution

Na+, Cl-, H20

what are the strongest oxidising and reducing agents in the electrolysis of aqueous NaCl

H2O and H2O

Why does water compose the two half equations in the electrolysis of aqueous NaCl

Because it is both the strong reducing agent and the strongest oxidising agent on the SEP table

what are the reactants in electrolysis of copper sulfate solution

CU2+, (SO4)2-, H2O

what are the strongest oxidising and reducing agents in the electrolysis of copper sulfate solution

oxidising agent is Cu2+ and reducing agent is H20

essential components of an electrolytic cell

source of electric current and conductors, positive and negative electrodes, and the electrolyte

When can the SEP table not be used in electrolysis

If an aqueous solution is concentrated (conc. > 1M)

what happens when electrolysis is performed under non-standard conditions

the electrode potentials of each half-equation changes

two types of electrodes that can be used

reactive and inert

what are reactive electrodes

electrodes that are consumed in the cell reaction

what are the possible reactants in electrolysis of CuSO4(aq) with copper electrodes

Cu2+, (SO4)2-, H2O, Cu

what is electrolysis used for in chemical industries

electroplating and electrorefining

another term for electroplating

metal plating

what components in an electrolytic cell are needed for electroplating

An electrode of the metal is at the anode and the electrolyte solution contains ions of the metal to be plated.

another term for Electrorefining

purification

in the purification of copper what is found at the two electrodes

Anode: Blister copper (impure Cu) and cathode: Copper (pure Cu)