Acids, Bases and pH Indicators

Acids and Bases are groups of chemical compounds, which react with each other to form salts and water. The reaction is known as a Neutralization process – in other words, acids and bases neutralize one another.

Acids

Acid solutions have a sour taste, they produce a burning sensation in contact with skin, and they are capable of dissolving many metals. Acids can be useful and also dangerous and poisonous.

Hydrochloric Acid(HCl) in the human stomach helps in the process of digestion. Vinegar is Acetic Acid (CH₃COOH), which is used in salad dressings and for food preservation, and we obtain Citric Acid(C₆H₈O₇) from oranges and lemons. Many types of cola contain Phosphoric Acid (H₃PO₄).

Sulfuric Acid (H₂SO₄), which is extremely harmful and corrosive to skin, is used in car batteries while Nitric Acid (HNO₃) is used in explosives and fertilizers.

Acids are classified as Organic if they contain carbon atoms, else they are termed Inorganic. Organic acids are used in beverages, cosmetics, detergents, foods, drugs, soaps, and plastics. Inorganic acids are generally much stronger and are used to manufacture paints, explosives, fertilizers, and other chemicals.

Bases or Alkalis

Bases are substances that react with an acid to decrease or neutralize its acidic properties. Bases dissolved in water are called Alkalis or Alkaline Solutions. Bases have a slippery texture and taste bitter.

Bases are also very useful chemicals. Sodium Hydroxide [NaOH] is used in the manufacture of soap, paper and synthetic materials. Calcium hydroxide [Ca(OH)₂] is used in bleaching powder and to neutralize soil acidity. Magnesium hydroxide [Mg(OH)₂] is a common laxative.

Acids and Bases in Chemistry

Acids dissolve in water to produce hydrogen ions. A hydrogen ion is a proton formed when a hydrogen atom loses its electron. Acid is also defined as a Proton Donor – it readily gives up a proton (hydrogen ion) to another substance. A base is able to accept a hydrogen ion from an acid – it is a Proton Acceptor.

However, all acids may not be able to release hydrogen and may not always be proton donors. In broader terms, therefore, all acids are defined as Electron-Pair Acceptors while bases are defined as Electron-Pair Donors – that is, acids can accept a pair of electrons from another atom or molecule while bases can share electron pairs with acids.

There are Strong Acids and Weak Acids, Strong Bases, and Weak Bases. Weak acids and bases do not ionize completely when dissolved in water, while strong acids are fully ionized. Sulfurous Acid (H₂SO₃) and Nitrous Acid(HNO₂) are weak acids but sulfuric acid and nitric acid are strong. Weak acids like vinegar can be consumed without any problem but strong acids like hydrochloric acid will burn skin in touch.

Check Point

1. Which is an organic acid?
   1. Acetic acid (CH₃COOH)
   2. Phosphoric Acid (H₃PO₄)
   3. Nitric Acid (HNO₃)
2. Bases dissolved in water are called _______ solutions.
3. Acids are Electron-Pair _______ while bases are defined as Electron-Pair _______.
4. Which of these is alkaline?
   1. Grapefruit juice
   2. Ammonia solution
   3. Saliva
   4. Black coffee
5. Litmus turns ______ in an acidic solution.

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