Chemistry of corrosion

This Module consists of three Web pages of required reading. The pagination is visible at the bottom of each page with direct links to adjacent pages. Introduction The driving force that causes metals to corrode is a natural consequence of their temporary existence in metallic form. To reach this metallic state from their occurrence in nature in the form of various chemical compounds (ores), it is necessary for them to absorb and store up for later return by corrosion, the energy required to release the metals from their original compounds. Compare the energy required to produce one metric ton of magnesium from its oxide to the energy required to convert enough copper oxide to produce one ton of metallic copper. Discuss the energy values presented in the Table shown on the page describing why metals corrode in relation to the order in which metals and associated alloys appeared in the history of mankind. When discussing the ionic content of an aqueous medium, the question often arises as to how acid (or alkaline) is the solution. Quite simply, this refers to whether there is an excess of H + (hydrogen) or OH-(hydroxyl) ions present. The H + ion is acid while the hydroxyl ion is alkaline or basic. The other ionic portion of an acid or alkali added to water can increases its conductivity or change other properties of the liquid, but does not increase or decrease its acidity. For instance, whether a given amount of H + ion is produced in water by introducing hydrochloric (HCl), sulfuric (H 2 SO 4), or any other acid is immaterial. The pH of the solution will be the same for the same number of dissolved hydrogen atoms. (reference) The pH may be measured with a meter or calculated if certain parameters are established. Water itself dissociates to a small extent to produce equal quantities of H + and OH-ions displayed in the following equilibrium: pH , originally defined by Danish biochemist Søren Peter Lauritz Sørensen in 1909, is a measure of the concentration of hydrogen ions. The term pH was derived from the manner in which the hydrogen ion concentration is calculated, it is the negative logarithm of the hydrogen ion (H +) concentration: where log is a base-10 logarithm and a H+ is the activity (related to concentration) of hydrogen ions. The "p" in Equation stands for the German word for "power", …