Chemistry: Acids and Bases

PROPERTIES OF ACIDS AND BASES

A. Acids

1. Properties of acids

• Aqueous solutions of acids have a sour taste. (Taste should NEVER be used as a test to evaluate any chemical substance.) Many acids, especially in concentrated solutions, are corrosive. Many are also poisons.
• Acids change the color of acid-base indicators.
• Some acids react with active metals to release hydrogen as, H2.
• Acids react with bases to produce salts and water.
• Acids conduct electric current. Because acids form ions in aqueous solutions, acids are electrolytes.

2. A binary acid is an acid that contains only 2 different elements: hydrogen and one of the more electronegative elements. Examples of binary acids include: HF, HCl, HBr, and HI.

3. Binary acid nomenclature:

• The name of the binary acid begins with the prefix hydro-
• The root of the name of the second element follows this prefix.
• The name then ends with the suffix -ic.

4. An oxyacid is an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal. Nitric acid, HNO3, is an oxyacid.

B. Some Common Industrial Acids

1. Sulfuric acid is the most commonly produced industrial chemical in the world.

• It is used in large quantities in petroleum refining and metallurgy as well as in the manufacture of fertilizer. It is also essential to a vast number of industrial processes, including the production of metals, paper, paint, dyes, detergents and many chemical raw materials.
• Sulfuric acid is an effective dehydration (water-removing) agent.

2. Pure nitric acid is a volatile, unstable liquid rarely used in industry or laboratories.

• The acid has a suffocating odor, stains skin, and can cause serious burns.
• It is used in making explosives, many of which are nitroen-containing compounds. It is also used to make rubber, plastics, dyes, and pharmaceuticals.

3. Phosphoric acid is used directly for manufacturing fertilizers and anmial feed.

• Dilute phosphoric acid is used as a flavoring agent in beverages and as a cleansing agent for dairy equipment.
• It is also important in the manufacture of detergents and ceramics.

4. Hydrochloric acid is important for "pickling" iron and steel, which is the immersion of metals in acid solutions to remove surface impurities.

• This acid is also used in industry as a general cleaning agent, in food processing, in the activation of oil wells, in the recovery of manesium from sea water, and in the production of other chemicals.

5. Concentrated acetic acid is a clear, colorless, pungent-smelling liquid known as glacial acetic acid. It has a freezing point of only 17 degrees celsius and can form crystals in a cold room.

• White vinegar contains 4-8% acetic acid.
• Acetic acid is important industrially in synthesizing chemicals used in the manufacture of plastics. It is a raw material in the production of food suplements and it is also used as a fungicide.

C. Bases

1. Properties of bases:

• Aqueous solutions of bases taste bitter. (Taste should NEVER be used to test a substance to see if it is a base.) Many bases are caustic; they attack the skin and tissues, causing severe burns.
• Bases change the color of acid-base indicators.
• Dilute aqueous solutions of bases feel slippery.
• Bases react with acids to produce salts and water.
• Bases conduct electric current. Bases form ions in aqueous solutions and are thus electrolytes.

D. Arrhenius Acids and Bases

1. An Arrhenius acid is a chemical compound that increases the concentration of hydrogen ions, H+, in aqueous solution.

• The acid will ionize in solution.

2. An arrhenius base is a substance that increases the concentration of hydroxide ions, OH-, in aqueous solution.

3. A strong acid is one that ionize completely in aqueous solution. The strength of an acid depends on the bond between hydrogen and the element to which it is bonded, and the ease with which that bond can be broken. Examples of strong acids: hydroiodic acid, hydrobromic acid, and sulfuric acid.

4. Acids that are weak electrolytes are known as weak acids. Examples of weak acids: hydrofluoric acid, acetic acid, and oxalic acid.

5. Organic acids, which contain the acidic carboxyl group--COOH, are generally weak acids.

6. Most bases are ionic compounds containing metal caations and the hydroxide anion. When a base completely dissociates in water to yield aqueous OH- ions, the solution is referred to as alkaline.

7. Not all bases are ionic compounds. Ammonia is a base because it produces hydroxide ions when it reacts with water molecules.

8. The strength of a base depends on the extent to which the base dissociates, or adds hydroxide ions to the solution. Strong bases arestrong electrolytes.

• Bases that are not very soluble do not roduce a large number of hydroxide ions when added to water.
• Many organic comopounds that contain nitrogen atoms are also weak bases. For example, ariline, a substance used to make dyes, is a weak base.