Year 12 Chemistry Coursework: The Magnesium Statue

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Year 12 Chemistry Coursework

The Magnesium Statue

Niall Boyle 12E


Planning

The Problem

A statue, which is made of an alloy consisting mainly of magnesium, corrodes at different rates, at different times of the year.

Background Knowledge

There are some areas of knowledge that should be taken into consideration to help in devising an experiment to help determine the cause of the problem, and which gave me a greater understanding of the problem.

A major factor in the decay of the statue is acid rain, which prevents the formation of the oxide coat that would normally form on magnesium preventing corrosion in air. Rain is naturally acidic, due to the CO2 dissolved in it, however when sulphur dioxide and oxides of nitrogen react with the rain water they form sulphuric, and nitric acids which make the rain strongly acidic.

SO2 + ½O2 + H2O → H2SO4

 It may also take the form of snow or fog. The sulphur dioxides and oxides of nitrogen come mainly from industry. Acid rain is currently a subject of great controversy because of widespread environmental damage for which it has been blamed, including eroding structures, injuring crops and forests, and threatening or depleting life in freshwater lakes. However the 1990 amendments to the Clean Air Act of 1967 put in place regulations to reduce the release of sulphur dioxide from power plants to 10 million tons per year by January 1, 2000. This amount is about one-half the emissions of 1990.

But still it shall be the rate of reaction that changes the speed of the statues decay, and chemical kinetics, the study of reaction rates, shows that three conditions must be met at the molecular level if a reaction is to occur:

  • The molecules must collide;
  • They must be positioned so that the reacting groups are together in a transition state between reactants and products;
  • And the collision must have enough energy to form the transition state and convert it into products.

This last condition is referred to as the activation energy, there must be enough energy for the particles to break their current bonds (form the transition state) and then form new bonds (the product). If even one of these conditions is difficult then the reaction shall normally be very slow. As such it has been found that there are four factors that can change the likelihood of all these conditions being met, these are:

  1. Concentration of reactants
  2. Temperature
  3. Surface area of a solid reactant
  4. Whether or not a catalyst is used

The concentration of a reactant affects the rate of reaction because the more concentrated it is, the more particles there are that can take part in the reaction. This means there shall be a greater number of collisions per second between the reactants, and the more collisions there are the more often the other two conditions are met, so the reaction will occur faster.

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The temperature of a compound is a measure of the energy with which it moves/vibrates. Some compounds move more than others do at the same temperature. If a compound has a high temperature it vibrates with more energy than if it was colder. If a reaction is carried out at a high temperature the particles will move with more energy and collide with more energy, as such it is more likely that the activation energy will be met during a collision.

Surface area is the area over which the reaction takes place, when dealing with larger solids it ...

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