Acid, Base and Salt

                                                Acid

 This article is about acids in chemistry. For other uses, see Acid (disambiguation).

"Acidity" redirects here. For the novelette, see Acidit

"Acidic" redirects here. For the band, see Acidic (band).y (novelette).

An acid is a molecule or ion capable of either donating a proton (i.e., hydrogen ion, H⁺), known as a Brønsted–Lowry acid, or, capable of forming a covalent bond with an electron pair, known as a Lewis acid.^[1]

The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H₃O⁺ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H⁺.

                                            

Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid.^[2] Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus/acēre, meaning 'sour'.^[3] An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute.^[1] A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict^[1] sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF₃), whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH₃). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H⁺) into the solution, which then accept electron pairs. However, hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids.^[4] Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. 

                                       Types Of Acids

   There are two basic types of acids organic and inorganic acids. Inorganic acids are sometimes referred to as mineral acids. As a group, organic acids are generally not as strong as inorganic acids. The main difference between the two is the presence of carbon in the compound; inorganic acids do not contain carbon.

• Inorganic acids – Inorganic acids are often termed mineral acids. The anhydrous form may be gaseous or solid. An inorganic anhydride is an oxide of metalloid which can combine with water to form an inorganic acid.

Example:

1. Sulphuric acid (H2SO4)
2.  Phosphoric acid (H3PO4)
3. Nitric acid (HNO3)

• Organic acids – Organic acids are corrosive and toxic. Corrosivity is a form of toxicity to the tissues that the acid contacts. Organic acids and their derivatives cover a wide range of substances. They are used in nearly every type of chemical manufacture. Because of the variety in the chemical structure of the members of the organic acid group.

Example:

1. Acetic acid
2. Citric acid
3. Formic acid

                                   Properties Of Acids

• (i)               Aqueous solutions of acids are electrolytes, meaning that they conduct electrical current. ...
• (ii)              Acids have a sour taste. ...
• (iii)             Acids change the color of certain acid-base indicates. ...
• (iv)             Acids react with active metals to yield hydrogen gas. ...
• (v)              Acids react with bases to produce a salt compound and water.
•                                             Uses Of Acids
•     

  1. Hydrochloric Acid (HCl)

  • Dilute hydrochloric acid is used in various industries that use heating applications. It is applied to remove deposits from the inside of the boilers.
  • Hydrochloric acid is also used for cleaning sinks and sanitary ware.

  2. Sulphuric Acid (H2SO4)
  Sulphuric acid is such an important industrial chemical that it is called the king of chemicals. Some of its major uses are as follows:

  • Sulphuric acid is used in car batteries.
  • It is used in the manufacture of paints, drugs, dyes, and to produce fertilizers.

  3. Nitric Acid (HNO3)

  • It is used by goldsmiths for cleaning gold and silver ornaments.
  • It is also used for the production of fertilizers such as ammonium nitrate.

  4. Acetic Acid (CH3COOH)

  • Acetic acid is used directly to enhance the flavour of food. In fact, we commonly know acetic acid as vinegar.
  • It is also used as a cleansing agent in products meant for cleaning windows, floors, utensils, etc.
  • It also helps to remove stains on woodwork such as furniture and carpets.
  • Acetic acid is used as a preservative in pickles, etc. Most microorganisms cannot live in an acidic environment. An acidic environment either slows down their activities or can also kill them. This is why you will find vinegar in many commonly packaged food items such as pickles, sauce, ketchups, etc.