ACIDS, BASES, AND SALTS
An acid is a substance that furnishes hydrogen ions (H+) when dissolved in water. For example, in its aqueous solution, hydrochloric HC1 (aq) dissociates as: HC1 (aq) → H+(aq) + Cl-(aq)
Some examples of acids are:
- Hydrochloric acid (HC1) in gastric juice.
- Carbonic acid (H2CO3) in soft drinks.
- Ascorbic acid (vitamin C) in lemon and many fruits.
- The citric acid in oranges and lemons.
- The acetic acid in vinegar.
- The tannic acid in tea.
- Nitric acid (HNO3) is used in laboratories.
- Sulphuric acid (H2SO4) is used in laboratories.
Strong and Weak Acid:
The acids that completely dissociate in water are called strong acids. Nitric acid completely dissociates in water HNO3(aq) → H+ (aq) NO - (aq) There are only seven strong acids:
- HCI-Hydrochloric Acid
- HBr-Hydrobromic Acid
- HI-Hydroiodic Acid
- HCIO-Perchloric Acid
- HCIO3-Chloric Acid
- H2SO4-Sulphuric Acid
- HNO3-Nitric Acid
The acids that dissociate partially in water are called weak acids. All organic acids like acetic acid and some inorganic acids are weak acids.
Since their dissociation is only partial, it is depicted by double half arrows.
HF(aq) H+(aq) + F-(aq)
The double arrows indicates here that:
(i) the aqueous solution of hydrofluoric acid not only contains H+(aq) and F-(aq) ions but also the dissociated acid HF(aq). (ii) there is an equilibrium between the dissociated acid HF (aq) and the ions furnished by it, H+(aq) and F-(aq)
- CH3COOH Ethanoic (acetic) acid
- HF Hydrofluoric acid
A base is a substance that furnishes hydroxide ions (HO-) when dissolved in water. For example, sodium hydroxide NaOH (aq),
In its aqueous solutions dissociates as:
NaOH (aq) → Na+(aq) + OH-(aq)
Strong Base and Weak Base:
These bases are completely dissociated in water to form the cation and hydroxide ion (OH).
KOH(aq) → K+(aq) + OH-(aq)
There are only eight strong bases. These are the hydroxides of the elements of the Groups 1 and 2 of the periodic table:
- LiOH Lithium hydroxide.
- NaOH Sodium hydroxide
- KOH Potassium hydroxide
Weak bases do not furnish OH- ions by dissociation. They react with water (OW). to furnish OH— ions.
NH3(g)+H2O(I) → NH4OH NH4OH(aq) NH+ (aq) + OH-(aq)
Examples of weak bases:
Difference between Acid and Base
Corrosive to metals
Slippery in nature
Blue to red
Red to blue
After adding base
After adding base
Salts are ionic compounds made of a cation other than an H+ ion and an anion other than an OH- ion.
Formation of salts: Salts are formed in many reactions involving acids and bases.
- By Neutralization of acids and bases: Salts are the product (besides water) of a neutralization reaction.
For example, Base Acid Salt Water
NaOH + HC1 → NaC1 + H2O
- By action of acids on metals: In a reaction between an acid and a metal, salt is produced along with hydrogen, Metal Acid Salt Hydrogen.
Zn + H2SO4 → ZnSO4 + H
- By action of acids on metal: Carbonates and hydrogen carbonates Salts are produced in reactions between acids and metal carbonates and hydrogen carbonates (bicarbonates) along with water and carbon dioxide.
CaCO3 + 2HC1 → CaC12 + H2O + CO
Type of salt and the nature of its aqueous solution:
Salt of Acid
Salt of Base
Nature of Salt Solution
pH (at 25°C)
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