Chemistry: Shipwrecks, Corrosion & Conservation1 The chemical composition of the ocean implies its potential role as an electrolyte1.1Identify the origins of the minerals in oceans as leaching by rainwater from terrestrial environments & hydrothermal vents in mid-ocean ridges: Sea water contains about 35g salts/L (this varies with temperature; higher temperature, higher concentration of salt) 78% of the oceans salt is NaCl; 16% is Mg salts; 6% is K salts Main cations and anions in sea water:CationsAnions

SodiumChlorides

PotassiumCarbonates

CalciumSulfates

MagnesiumBromides

Leaching by rainwater from terrestrial environment: Rainwater seeps over the Earth, dissolving minerals from rocks and soils, and carries them via ground water or rivers into the oceans The ions dissolved vary according to the composition of the rocks/soil through which the water gets into (i.e. water that had moved through limestone would be high in calcium and carbonate ions)Hydrothermal vents in mid-ocean ridges: Hydrothermal vents occur where tectonic plates are separating (mid-ocean ridges) and at hot spots in plates. At these places, molten material is rising from the mantle Rocks form from cooling molten material which solidifies As the igneous rocks cool, they crack; allowing cold sea water to sink into the rocks and heat the water to about 350oC-400oC by the hot magma The water then expands and rises through the rocks, bringing insoluble sulfides of copper, zinc and iron into the oceans water. Soluble ions in the water include sodium, potassium, magnesium, chloride, sulfate and bromide

1.2Outline the role of electron transfer in oxidation-reduction reactions: An oxidation-reduction reaction occurs between two substances when electrons are lost by one reacting species (reductant) and gained by another (oxidant) Oxidation involves the loss of electrons (OIL) Reduction involves the gain of electrons (RIG) Oxidation and reduction reactions occur simultaneously for each species that loses an electron, another species must gain an electron

1.3Identify that oxidation-reduction reactions can occur when ions are free to move in liquid electrolytes: Electrolyte: a liquid that can conduct electricity because they have ions free to move Electrons can be transferred in electrolytes, thus redox reactions can occur as the electrons are transferred from one species in the electrolyte to another Without the electrolyte, there would be no way for the ions in reactions to move away to make room for further reaction

1.4Describe the work of Galvani, Volta, Davy and Faraday in increasing understanding of electron transfer reactions:Galvani: In his experiments on a dissected frog, he noticed that the muscle contracted when two different metals were in contact with both the spinal cord and the leg muscle of the frog He called this animal electricityVolta: Further investigated Galvanis effect and realised that the current was generated by the two metals, not the dead animal Volta then developed the first battery, a voltaic pile made of alternating zinc and copper disks with an electrolyte solution in between This enabled further experiments to be conducted by others such as DavyDavy: Davy used Voltas device to pass electricity through compounds, resulting in the decomposition of some compounds previously classified as elements, i.e. H2O, NaCl Made important discoveries in electrochemistry that led to corrosion protection for ships hulls Discovered several active elements including Na, K, Ca, Sr, Ba and MgFaraday: Continued on from Davys experiments and extended them Quantified electrolysis by relating the quantity of electricity used in electrolysis to the valency and mass of the element produced Formulated laws of electrolysis Developed terminology we use today; anode, cathode, electrodes, ion, anions, cationsThe Significance of their Findings: They all advanced the knowledge and understanding of electrochemistry Galvanis, and later Voltas experiments led to the development of the first device for generating a continuous electric current the battery Davy then examined the decomposition by electrolysis and discovered several active elements Their combined work showed the relationship between chemical bonds and electricity They began the first step in understanding how electron transfer reactions work

2 Ships have been made of metals or alloys of metals2.1Account for the differences in corrosion of active and passivating metals: Corrosion is the oxidation of metals and alloys due to chemicals in the environment The most common form of corrosion is the rusting of iron Causes many environmental problems, i.e. oil spills due to ship and pipelines corroding. It is expensive to have to constantly replace corroded materials. Also, the failure of metal parts can endanger lives.The corrosion of active metals: Generally, the more active the metal, the more quickly/easily it will corrode Metals higher up in the activity series are more susceptible to reacting with oxygen, water and dilute acids in the environment Active metals corrode easier because they lose electrons more readilyThe corrosion of passivating metals: Passivating metals are reactive metals that form an inactive, protective coating as a result of reaction with substances such as oxygen Chromium and aluminium are passivating metals. They react with the atmosphere, forming an oxide that is inert, non-porous and adheres to the surface 4Cr(s) + 3O2(g) 2Cr2O3(s) 4Al(s) + 3O2(g) 2Al2O3(s) If removed, the protective coating quickly reforms (provided oxygen is available) and protects the metal from further corrosion

2.2Identify iron and steel as the main metals used in ships: The main metal used in the hulls of ships is iron, in the form of steel alloys Iron/steel is suitable for this use because it is strong, hard and malleable and it can be made relatively corrosion resistant by the use of alloyed elements (e.g. stainless steel)

2.3Identify the composition of steel and explain how the percentage composition of steel can determine its properties: Steel is iron with 10.5% chromium content and possibly nickel, manganese, silicon and