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Redox reactions
Redox reactions are reactions which involve the transfer of electrons, e.g. rusting and burning
Oxidation
Oxidation is any process by which an entity loses electrons
Reduction
Reduction is any process by which an entity gains electrons.
An oxidation number
An oxidation number is a numerical value that represents the indicates how many electrons an atom has gained, lost, or shared in forming a chemical bond.
Oxidation is the increase in oxidation number.
Reduction is the decrease in oxidation number.
An oxidation agent
An oxidation agent is a substance that brings about the oxidation in other substances.
A reducing agent
A reducing agent is a substance that brings about reduction in other substances.
Valency vs Oxidation Numbers
Valency | Oxidation Numbers |
Does not carry a + or – sign. | Can be positive or negative. |
Always a whole number. | Can be fractions. |
The electrochemical series; metals are arranged in order of their reactivity / tendency to be oxidised / lose their electrons.
Displacement Reactions
Displacement reactions occur when a metal from the electrochemical series is mixed with the ions of a metal lower down in the series.
The atom of the more reactive metal push their electrons on to the ions of the less reactive metal. As a result, the more reactive metal is oxidised and the least reactive metal is reduced
Use of electrochemical series
Predict results of chemical reactions.
TO use a less valuable ion to displace a more valuable and less reactive, from a solution of it’s salt. Each metal will displace a metal that is below the series and from a solution of it’s ions.
Electroplating
An electrochemical cell
An electrochemical cell is a device that generates electrical energy from chemical reactions or uses electrical energy to drive chemical reactions.
Electrolysis
Electrolysis: electrolytes are chemically changed and broken up when electric current is passed through them.
In electrolysis, electrodes which are conductors are connected to the positive and negative terminal of a d.c Power Supply and are dipped into an electrolyte in aq. Solution.
electrolyte
An electrolyte is a substance that conducts electricity when dissolved in water or when molten.
Electrolysis process:
In electrolysis, electrodes which are conductors are connected to the positive and negative terminal of a d.c Power Supply and are dipped into an electrolyte in aq. Solution.
Positive ions (cations) are attracted to the negative electrode (cathode).
Negative ions (anions) are attracted to the positive electrode (anode).
Oxidation occurs at the anode.
Reduction occurs at the cathode.
Cations are reduced (gain electrons), and anions are oxidized (lose electrons).
sacrificial electro method
Galvanic / Voltaic and Simple cell
There is one anode and one cathode, both dipped in an electrolyte solution and connected by a salt bridge.
The anode is a more electropositive or electroreactive metal. It creates an electrochemical potential and therefore gets oxidized, losing electrons. These electrons travel through the external circuit to the cathode, where reduction occurs.
As a result, the anode loses mass as its metal atoms dissolve into the electrolyte as positive ions.
This movement of electrons generates electric current.
The greater the electrochemical potential difference (difference in reduction potentials) between the two electrodes, the higher the voltage of the cell.
Differences between Simple Cell and Electrolysis
A galvanic cell generates electricity through spontaneous chemical reactions, while an electrolytic cell requires an external energy source to drive non-spontaneous reactions.
Reactions in a galvanic cell occur spontaneously, whereas reactions in an electrolytic cell are non-spontaneous.
Corrosion
Corrosion is the gradual deterioration of metals caused by chemical or electrochemical reactions with their environment. It typically involves the oxidation of the metal, in the presence of oxygen and moisture.
This process results in the formation of compounds like oxides, hydroxides, or sulfides, leading to structural weakening and property changes in the metal.
Ways to stops corrosion:
1.) Using a barrier such as paint or oil, to stop oxygen and water getting in contact with the metal.
2.) Electroplating – this involves coating the iron or steel with corrosion resistant metal, using electricity, such as chrome plating.
3.) Galvanizing – a thin layer of zinc is added to the iron or steel, by electroplating. The zinc layer is oxidised, forming a water resistant layer of zinc oxide.
4.) Using a sacrificial electro method; one more electro reactive metal is oxidised rather than another; zinc electrodes in contact with hull of ship causes zinc to lose electrons rather than iron.
