Acid and Base

Acid
Some common acids we know Citric acid in lemon Lactic acid in curd Tartaric acid in tamarind.Taste of all three are sour. Acid is sour in taste but beware of tasting any other acid. It is corrosive in nature. Corrosive nature of acid may turn the marble colour into a light colour. Continuous action of lime turn kitchen slab dull. Some common acids are HCl – Hydrochloric acid HNO₃ – Nitric acid H₂SO₄ – Sulphuric acid All acids have electro-positive Hydrogen ion. Acid reacts with metals to liberate H₂.

For example

2HCl + Zn -> ZnCl₂ + H₂

H₂SO₄ + Cu -> CuSO₄ + H₂

HNO₃ + Ag -> AgNO₃ + H₂

Metallic carbonate and metal hydrogen carbonate

Na₂CO₃ + 2HCl -> 2NaCl + H₂O + CO₂ NaHCO₃ + HCl -> NaCl + H₂O + CO₂

CaHCO₃ + H₂SO₄ -> CaSO₄ + H₂O + CO₂

Metallic carbonates react with acid to liberate carbon dioxide, metallic salt and water.

Metallic carbonate + Acid -> Salt + Carbon dioxide + Water

Metallic hydrocarbonate + Acid -> Salt + Carbon dioxide + Water

To test acid we use synthetic agents like

1. Methyl Orange
2. Phenolphthalein

An interesting fact Litmus solution is a purple coloured solution which is obtained from lichen a thallophyte. Litmus is neither acid nor basic in nature but when it reacts with acid or base it changes color.

Red Litmus + Acid -> Blue Blue Litmus + Base -> Red

There are many natural products which symbolize presence of acid or base. For e.g. red cabbage, turmeric, petunia, china rose, geranium.

Base
All bases do not dissolve in water. Bases are salty in taste. It is harmful to touch a base. Common base are NaOH, KOH, Ca(OH)₂.

How do you identify a base? OH are the constituent of the base. In a molar solution, the amount of H and OH ions present determines the concentration of the solution. Weak and strong acid and base are determined by the concentration of H and OH ions. To test the ionic capacity and weakness of the base, we take pH test.   Acid and base react together to form salt and water.

Acid + Base -> Salt + Water.

HX + YOH -> XY + H₂O

HCl + NaOH -> NaCl + H₂O

HNO₃ + KOH -> KNO₃ + H₂O

2H₂SO₄ + 2Mg(OH)₂ -> 2MgSO₄ + 2H₂O

When electricity is passed in the solution of sodium chloride (Common salt) and water, it yields sodium hydroxide. The reaction takes place as follows

NaCl + 2H₂O -> 2NaOH + Cl₂ + H₂

ph Scale – Potenz (Power) of hydrogen

pH is used to find the concentration of hydrogen ion.

Acid are electron donors whereas bases are electron acceptors. H+ and OH -Antacids are made of Aluminum hydroxide and Magnesium hydroxide.

Nettle Dock relationship
Person stung by nettle leaves is affected by methanoic acid. Dock leaf has alkaline properties. Rubbing dock leaves on nettle sting rashes soothes pain. Ant venom also has methanoic acid. Methanoic acid is also known as formic acid. Its chemical formula is HCOOH.

Amphoteric substance

Those substance which act as acid and base in different situation are called amphoteric substance e.g. H₂O, Al(OH)_3.

Al(OH)₃+OH ->Al (OH)₄

3H+Al(OH)₃->3H₂O+Al_.

Other examples –

• NH4 Ammonium salt behaves as acid and amides as base.
• Acetic acid (CH₃COOH) otherwise an acid acts as base when it reacts with HCl.

Important solvent dimetyl sulfoxide (DHSO₂) & acetonitrile (CH₃CN) are used to measure acid dissociation constant of organic molecules