Acids, Bases and Salts (Class VI- Chemistry)

Acids and bases are two fundamental categories of chemical substances with distinct properties and significant roles in various chemical reactions and processes. Understanding their nature, reactions, and applications is essential for many scientific and industrial fields.

Acids

Acids are substances that have a sour taste and are corrosive in nature. They have the ability to turn blue litmus paper red due to their acidic properties. Common examples of acids include:

• Orange Juice: Contains citric acid.
• Curd: Contains lactic acid.
• Vinegar: Contains acetic acid.
• Hydrochloric Acid (HCl): A strong mineral acid used in various industrial processes.

Acids play crucial roles in digestion, food preservation, and chemical synthesis.

Bases

Bases are substances that are slippery to the touch in aqueous solutions and have a bitter taste. They can turn red litmus paper blue, indicating their basic nature. Examples of bases include:

• Soap: Often contains sodium hydroxide.
• Ammonium Hydroxide (NH4OH): Used in cleaning products.
• Calcium Hydroxide (Ca(OH)2): Also known as slaked lime, used in construction.

Bases are essential in neutralizing acids, manufacturing soaps, and other chemical applications.

Neutralization Reaction

A neutralisation reaction occurs when an acid reacts with a base to form salt, water, and heat. This reaction effectively neutralizes the acidic and basic properties of the reactants. A classic example of a neutralisation reaction is:

HCl +NaOH -> NaCl +H₂O

In this reaction, hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to produce sodium chloride (table salt) and water.

Salts

Salts are products formed from the neutralisation reaction of acids and bases. They can be acidic, basic, or neutral in nature depending on the strengths of the reacting acid and base. For example, sodium chloride (NaCl) formed from HCl and NaOH is a neutral salt.

Visual Indicators

Indicators are substances used to test whether a substance is acidic or basic by changing color. They are essential tools in chemistry for identifying the nature of solutions.

Natural Indicators

• China Rose: Changes color in acidic and basic solutions.
• Turmeric: Turns red in basic solutions but remains yellow in acidic solutions.
• Litmus: Litmus is a natural indicator extracted from lichens. It is available as a solution or paper strips:
  • Red Litmus Paper: Turns blue in basic solutions.
  • Blue Litmus Paper: Turns red in acidic solutions.

Phenolphthalein

Phenolphthalein is a synthetic indicator that is colorless in acidic solutions but turns pink to red in basic solutions. It is commonly used in titrations to determine the endpoint of acid-base reactions.

Olfactory Indicators

Olfactory indicators are substances whose smell changes when mixed with acidic or basic solutions. Examples include:

• Onion: Loses its characteristic smell in basic solutions.
• Clove Oil and Vanilla Extract: Change their smell based on the solution’s pH.

Neutralisation in Daily Life

Neutralisation reactions are crucial in many everyday situations:

• Indigestion Relief: Milk of magnesia (magnesium hydroxide) neutralizes excess stomach acid.
• Ant Sting Treatment: Baking soda neutralizes formic acid from ant stings.
• Soil pH Adjustment: Farmers treat soil with acids or bases to maintain a neutral pH for optimal plant growth.
• Factory Waste Treatment: Acidic wastes are neutralized with bases before being discharged to prevent environmental damage.

Recap of Concepts

Safety Measures While Using Acids and Bases

• Always pour acid into water, not water into acid, to prevent splattering.
• Wear safety gloves when handling acids and bases to avoid skin burns and injuries.

Uses and Applications

pH of Soil

Excessive use of chemical fertilizers can alter the soil’s pH, making it too acidic or too basic for plants to grow. Substances are added to the soil to neutralize its pH, ensuring a suitable environment for plant growth.

Common Uses of Acids

• Food Preservation: Citric acid is used as a preservative.
• Aerated Drinks: Contain carbonic acid.
• Baking Powder: Contains tartaric acid to help dough rise.
• Cooking: Vinegar (acetic acid) is used in various culinary processes.

Common Uses of Bases

• Manufacture of Soaps: Sodium hydroxide is used in soap making.
• Bleaching Powder: Calcium hydroxide is used in its production.
• Fire Extinguishers: Aluminium hydroxide acts as a foaming agent.

Knowing about the properties, reactions, and applications of acids and bases is essential in both everyday life and industrial processes. They play a crucial role in various chemical reactions, from neutralizing stomach acid to manufacturing products. Proper handling and knowledge of these substances are vital for their safe and effective use.