Acid
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.
Summary
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.
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.
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Acid
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:
CH3COOH → H+ + CH3COO-
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. |
Lesson
Acid, Base and Salt
Subject
Science
Grade
Grade 8
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