Acids, Bases, Oxides

Acids

An acid (often represented by the generic formula HA [H+A−]) is
‎traditionally considered any chemical compound that, when dissolved ‎in water, gives a solution with a hydrogen ion activity greater than in ‎pure water, i.e. a pH less than 7.0. That approximates the modern ‎definition of Johannes Nicolaus Brønsted and Martin Lowry, who ‎independently defined an acid as a compound which donates a ‎hydrogen ion (H+) to another compound (called a base). Common ‎examples include acetic acid (in vinegar) and sulfuric acid (used in car ‎batteries). Acid/base systems are different from redox reactions in that ‎there is no change in oxidation state.‎
Chemicals or substances having the property of an acid are said to be ‎acidic (adjective).‎
The word "acid" comes from the Latin acidus meaning "sour," but in ‎chemistry the term acid has a more specific meaning.‎
Properties:‎
Brønsted–Lowry acids:‎
• Are generally sour in taste. (For example, the sour taste of lemon ‎juice is due to citric acid) ‎
• Strong or concentrated acids or their fumes often produce a ‎stinging feeling on mucous membranes ‎
• Change the color of pH indicators as follows: turn blue litmus ‎and methyl orange red, turn phenolphthalein colorless ‎
• React with metals to produce a metal salt and hydrogen ‎
• React with metal carbonates to produce water, CO2 and a salt ‎
• React with metal hydroxides and metal oxides to produce water ‎and a salt ‎
• Conduct electricity


Bases

In chemistry, a base is most commonly thought of as an aqueous ‎substance that can accept protons. A base is also often referred to as an ‎alkali if OH− ions are involved. Alternate definitions of bases include ‎electron pair donors (Lewis), as sources of hydroxide anions ‎‎(Arrhenius). Examples of simple bases are sodium hydroxide and ‎ammonia.‎
Bases can be thought of as the chemical opposite of acids. A reaction ‎between an acid and base is called neutralization. Bases and acids are ‎seen as opposites because the effect of an acid is to increase the ‎hydronium ion (H3O+) concentration in water, whereas bases reduce ‎this concentration. Bases react with acids to produce water and salts (or ‎their solutions).‎
Some general properties of bases include:‎
Slimy or soapy feel on fingers, due to saponification of the lipids in ‎human skin ‎
Concentrated or strong bases are caustic (corrosive) on organic matter ‎and react violently with acidic substances ‎
Aqueous solutions or molten bases dissociate in ions and conduct ‎electricity. ‎
Reactions with indicators: bases turn litmus paper blue and ‎phenolphthalein pink

Oxides

An oxide is a chemical compound contaning at least one oxygen atom ‎as well as at least one other element. Most of the Earth's crust consists ‎of oxides. Oxides result when elements are oxidized by oxygen in air. ‎Even materials that are considered to be pure elements often contain a ‎coating of oxides. For example, aluminium foil has a thin skin of Al2O3 ‎that protects the foil from further corrosion.‎
Virtually all elements burn in an atmosphere of oxygen. In the presence ‎of water and oxygen (or simply air), some elements - lithium, sodium, ‎potassium, rubidium, caesium, strontium and barium - react rapidly, ‎even dangerously, to give the hydroxides. In part for this reason, alkali ‎and alkaline earth metals are not found in nature in their metallic, i.e., ‎native, form. Caesium is so reactive with oxygen that it is used as a ‎getter in vacuum tubes, and solutions of potassium and sodium, so ‎called NaK are used to deoxygenate and dehydrate some organic ‎solvents. The surface of most metals consist of oxides and hydroxides ‎in the presence of air. A well known example is aluminium foil, which ‎is coated with a thin film of aluminium oxide that passivates the metal, ‎slowing further corrosion. The aluminium oxide layer can be built to ‎greater thickness by the process of electrolytic anodising. ‎
Due to its electronegativity, oxygen forms chemical bonds with almost ‎all elements to give the corresponding oxides. So-called noble metals ‎‎(common examples: gold, platinum) resist direct chemical combination ‎with oxygen, and substances like gold(III) oxide must be generated by ‎indirect routes