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9.6 Shipwrecks, Corrosion and Conservation: 1. The ocean as an electrolyte
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1. The chemical composition of the ocean infers its
potential role as an electrolyte
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Students learn to:
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Students: |
Extract from Chemistry Stage 6 Syllabus (Amended
October 2002). © Board of Studies, NSW.
[Edit: 7 Jul 09]
Prior learning: Preliminary module 8.4.4
Background: The oceans contain many dissolved substances, mostly as positive and negative ions. These ions are able to move freely and therefore can carry an electric current. Oxidation-reduction reactions (redox reactions) frequently occur in this environment.
describe the work of Galvani, Davy, Volta and Faraday in increasing understanding of electron transfer reactions
- These four scientists made important contributions to the development of our understanding of electricity and electrochemistry
- 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.
- 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 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 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.
process information from secondary sources to outline and analyse the impact of the work of Galvani, Volta, Davy and Faraday in understanding electron transfer reactions
- Information on these scientists can be gathered
from many general texts, encyclopaedias and from
the World Wide Web. See an original drawing of
Galvani's experiment
, Geocities.com. Scroll down to see an engraving of his experiment and some notes. - When you have the information you need,
process the information by assessing its
reliability.
It is important to distinguish between outlining and analysing the work of each scientist. - Your outline should be a brief description of their works.
- Your analysis of the impact of the work of Galvani, Volta, Davy and Faraday should show how each scientist used and developed earlier ideas to improve our understanding of electron transfer reactions.
Selected classic papers Classic Chemistry site, Le Moyne
College, New York, USA.
Information on Galvani, Volta, Davy and Faraday is available in the History of Electrochemistry,
Florida Community College, Jacksonville, USA
identify the origins of the minerals in oceans as:
- leaching by rainwater from terrestrial environments
- hydrothermal vents in mid-ocean ridges
- 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.
- 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.
- 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.
Read about Why
is the ocean salty? by Herbert Swenson, U.S.
Geological Survey, Colorado, USA and
Hydrothermal Vents , which includes a 3.5 Mb video clip of
a smoker. The Extreme 2000, Voyage to the deep, National
Science Foundation, the University of Delaware College of
Marine Studies, Philadelphia, USA.
outline the role of electron transfer in 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 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.
Further Information
Half equations are used to describe both oxidation and reduction reactions
Net ionic equations are commonly used to describe oxidation-reduction reactions.
The mnemonic “OIL RIG” is useful for remembering the difference between oxidation and reduction:
Oxidation Is Loss of electrons.
Reduction Is Gain of electrons.
identify that oxidation-reduction reactions can occur when ions are free to move in solid and liquid electrolytes
- 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.
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