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An acid is a substance which dissociates in water to give positively charged hydrogen (H+). Acids are generally sour in taste and react with the base to produce salt. This note contains further information about acid, its chemical and physical properties.

Inorganic compounds can broadly be classified into three main classes namely acids, bases and salt. This classification is based primarily on the fact that each class has own characteristics properties.

An acid is a substance which dissociates in water to give positively charged hydrogen (H+). H+ is called hydrogen ion. Acids have the sour taste and turn blue litmus paper into red, react with carbonates to give carbon dioxide and with metallic oxides to give salts and water.

The dissociation of Hydrochloric acid is given as:

HCl → H+ + Cl-

The dissociation of acetic acid in aqueous solution is represented as:


Some strong acids are commonly used in the laboratory. They are:

S.N. Name Formula
1. Hydrochloric acid HCl
2. Sulfuric acid H2SO4
3. Nitric acid HNO3

Acids in nature

Generally acid denotes a substance which tastes sour but in chemistry, its meaning is not limited up to this concept only. Most substances that contain acid taste sour due to the presence of H+ ion. Example of some acids that we can gain through fruits and vegetables are:

S.N Acids Sources
1. Citric acid Lemons, tomatoes
2. Acetic acid Vinegar
3. Carbonic acid Soda water
4. Hydrochloric acid Stomach
5. Tartaric acid Fruits
6. Ascorbic acid Citrus fruits
7. Formic acid Ants(produced by ant bite)
Characteristics of acid

Physical properties

1. They all contain hydrogen.

2. They possess sour taste.

3. Many acids are corrosive.

4. They turn blue litmus red.

5. They turn methyl orange into yellow color.

Chemical properties

1. Dilute acids react with some metals like zinc, magnesium etc. to form the salt and release hydrogen gas. The metals replace the hydrogen of acids to form a salt.

Mg + 2HCl → MgCl2 + H2.

Hydrochloric acid Magnesium chloride

Zn + H2SO4 → ZnSO4 + H2

Zinc + Sulphuric acid → Zinc sulphate + Hydrogen

2. Dilute acids decompose bicarbonate and carbonates and liberate carbon dioxide.

NaHCO3 + HCl → NaCl + H2O + CO2

Sodium bicarbonate + Hydrochloric acid → Salt + Water + Carbondioxide

3. They neutralize alkali-forming salt and water.

NaOH + HCl → NaCl + H2O

(Alkali) (Acid) (Salt) (Water)

4. They react with metallic oxides to give salt and water.

Na2O + 2HNO3 → 2NaNO3 + H2O

Sodium Oxide + Nitric Acid → Sodium nitrate + Water

5. They dissolve in water to produce hydrogen ions (H+).

Uses of acid

a. Tannic acid is used to tan leather.

b. Sulfuric acid is used in the manufacture of ammonium sulphate.

c. Sodium bicarbonate is used to make baking powder.

d. Hydrochloric acid, sulphuric acid, and nitric acid are used in the laboratory.

Differences between acids and bases:

S.N Acids Bases
1. Turn blue litmus into the red. Turn red litmus into blue.
2. React with metals to give a salt and hydrogen gas. Normally do not react with metals. Only some metals like zinc, aluminum and tin react to give hydrogen.
3. Are corrosive to skin. Are slippery to touch.
4. Are sour in taste. Are bitter in taste.
5. React with bases to give salts and water. React with acids to give salt and water.
6. Aqueous solutions of acids contain replaceable hydrogen ions. Aqueous solution of the base contains replicable hydroxyl ions.
7. Give no color with phenolphthalein. Give red color with phenolphthalein.
Things to remember
  • An acid is a substance which dissociates in water to give positively charged hydrogen (H+). ‘H+’ is called hydrogen ion. Acids have sour taste and turn blue litmus into red, reacts with carbonates to give carbon dioxide and with metallic oxides to give a salt and water.
  • A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved in water. Sodium hydroxide and ammonia are bases because they give hydroxyl ions in water.
  • A salt is a compound formed by the partial or complete neutralization of an acid by a base. A salt is a neutral substance. It does not have acidic and basic properties. Some salt are salty while most of them taste bitter.
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.
Videos for Acid
Acid Bases and Salts
Acidic, Basic and Neutral Salts
Acids & Bases, Properties & Characteristics of Acids & Bases
Questions and Answers

An acid is a substance that gives hydrogen ions when dissolved in water. The physical properties of acid are:

  • Acid have sour taste
  • It turns blue litmus paper into red
  • Acids have high dissolving power and dissolve many substances. Some metals like zinc, magnesium react with acids like dilute sulphuric acid and dilute hydrochloric acid to produce a salt of the acid and hydrogen.
    Zn + 2HCl → Zncl2 + H2
  • The acid reacts with a base to give salt and water.
    HCl + NaOH → NaCl + H2
  • An acid gives H+ ions when dissolved in water.
    HCl = H+ + Cl-
  • Theacid reacts with metallic carbonate to produce carbon dioxide.
    2Cl + CaCo3 → CaCl2 + CO2 + H2O

The differences between acid and base are as follows:

The acid gives hydrogen ion when dissolve in water. Base gives hydroxyl ion when dissolve in water.
It turns blue litmus into a red. It turns red litmus into blue.
It has a sour taste. It has bitter taste.

Orange and lemons have sour taste because they contain citric acid on them.

Acids should be handled with care because, generally concentrated acid are corrosive in nature and harm to our skin.

An acid – Nitric acid
A soluble base – Aluminum Hydroxide
A salt – Sodium Chloride
An Indicator – Litmus paper


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