Shipwrecks, Corrosion and ConservationSummary Slides PART 1 – Jack Dengate

Origins of Minerals in Oceans

• Sea water is an electrolyte solution containing about 0.5 mol L–1 of sodium chloride and significant concentrations of other ions. 

• Sea water is typically about 3.5% salts by mass and has a pH about 8.

Origins of Minerals in Oceans

• Rain and ground water dissolve salts from the soil and rock layers.

• This process is known as leaching. The salts are carried to the oceans by rivers.

Origins of Minerals in Oceans

• Volcanic activity near mid-ocean ridges is responsible for the occurrence of some dissolved salts in sea water.

• The hydrothermal vents release hot water, rich in salts, into cold sea water.  The lower temperature causes some mineral deposits to form on the ocean floor.

Oxidation – Reduction Reactions

• Oxidation-reduction reactions are also known as either redox reactions or electron transfer reactions.

• Oxidation reactions and reduction reactions always occur together.

Oxidation – Reduction Reactions

• Oxidation involves a loss of electrons.

• Reduction involves a gain of electrons

• Electrons transfer can occur directly between reactants or from the oxidation reaction site through a conductor to the reduction reaction site.

Sea water as an electrolyte solution

• In oxidation-reduction reactions electrons move from the reductant undergoing oxidation to the oxidant undergoing reduction

• An oxidation-reduction reaction will only occur if ions are free to move and an electrochemical cell is produced.  The electrical circuit must be complete and there should be no accumulation of charge.

• Sea water is an electrolyte solution in which ions are free to move and where oxidation-reduction reactions readily take place.

Luigi Galvani

• Luigi Galvani was the first person to generate an electric current effect in frog's legs using two different metals. 

• He explained the electricity as being of animal origin. 

Allesandro Volta

• Alessandro Volta did not agree with Galvani's explanation.

• Volta was stimulated to develop the first electric battery from two different metals separated by a conducting solution of salt.

Humphry Davy

• Humphry Davy used electricity as a source of energy for some of his investigations involving chemicals. 

• He decomposed water by electrolysis and was responsible for isolating many metals in a pure form, including the reactive metals sodium and potassium.

Michael Faraday

• Michael Faraday carried out quantitative research into electrochemistry, developed laws of electrolysis and introduced terms such as anion and cation to explain what was happening in terms of particle theory.

• These four scientists made important contributions to the development of our understanding of electricity and electrochemistry