Metal Corrosion, Chemical Reactions, and Electrochemistry

Metal Corrosion

Corrosion is the rusting of metal or alloy due to moisture and air. When it contacts air and water, a reaction forms a layer on the surface. For example, when an iron rod contacts air and moisture, it reacts and forms ferric oxide (Fe₂O₃) on its surface. It can be prevented by using alloys like stainless steel, brass, or bronze, painting the metal, applying oil, or coating with galvanized zinc.

Chemical Reactions

Some reactions happen very fast, like the precipitation of silver chloride, which occurs immediately after mixing aqueous solutions of silver nitrate and sodium chloride. Other reactions, like the rusting of iron in the presence of air and moisture, are very slow. Some reactions have a moderate rate.

The rate of a chemical reaction is the change in concentration of a reactant or product per unit time. Specifically, it can be expressed as:

• The rate of decrease in the concentration of any reactant
• The rate of increase in the concentration of any product

Peptization

Peptization is the formation of a colloid by breaking up a precipitate using an electrolyte (peptizing agent) to disperse into a colloid. For example, clay will normally precipitate in water, but using sodium carbonate as a peptizing agent, clay can form a colloid with water.

Peptization or deflocculation is the process responsible for the formation of stable dispersion of colloidal particles in a dispersion medium. It can be defined as converting a precipitate into a colloidal sol by shaking it with a dispersion medium in the presence of a small amount of electrolyte.

Electroosmosis

Electroosmotic flow (EOF), or electroosmosis, is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane, microchannel, or any other fluid conduit.

Friedel-Crafts Reactions

Friedel-Crafts reactions attach substituents to an aromatic ring. They are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.

Clemmensen Reduction

The Clemmensen Reduction allows the deoxygenation of aldehydes or ketones to produce the corresponding hydrocarbon.

Sandmeyer Reaction

The Sandmeyer reaction synthesizes aryl halides from aryl diazonium salts using copper salts as reagents or catalysts. It is an example of a radical-nucleophilic aromatic substitution.

Conductors and Insulators

In a conductor, electric current flows freely; in an insulator, it cannot. Metals like copper are typical conductors, while most non-metallic solids are good insulators, having high resistance to the flow of charge. Most atoms hold onto their electrons tightly and are insulators.