Acids and Bases

Acids and bases are common chemicals that react together to form salt and water. The word “acid” comes from the Latin word ‘acere,’ meaning ‘sour.’

In daily life, we use many acids. For example, citric acid is found in orange juice, lactic acid in sour milk, and acetic acid in vinegar. These acids and bases combine to form chemical bonds, helping us understand their properties.

Definitions:

• Acid: A substance that donates a hydrogen ion (H+). It tastes sour and turns blue litmus paper red.
• Base: A substance that accepts a hydrogen ion. It tastes bitter, feels slippery, and turns red litmus paper blue.

Types of Definitions:

• Arrhenius Definition: Acids produce H+ ions, and bases produce OH- ions in a solution.
• Bronsted-Lowry Definition: Acids donate protons (H+), and bases accept protons.
• Lewis Definition: Acids accept electron pairs, and bases donate electron pairs.

pH Scale:

The pH scale measures how acidic or basic a substance is, ranging from 0 (most acidic) to 14 (most basic). Litmus paper can also be used to test this: blue paper turns red for acids, and red paper turns blue for bases.

Properties:

• Acids:

  • Corrosive
  • Conduct electricity
  • pH less than 7
  • Produce hydrogen gas with metals
  • Example: Sulfuric acid (H2SO4), Hydrochloric acid (HCl)

• Bases:

  • Slippery
  • Release OH- ions in water
  • Conduct electricity
  • pH greater than 7
  • Example: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)2)

• Neutral Substances:

• • Neither acidic nor basic
  • pH of 7
  • No effect on litmus paper
  • Example: Water (H2O), Common salt (NaCl)

Differences:

• Acids: Release H+ ions, turn blue litmus red, taste sour, pH 1-7.
• Bases: Release OH- ions, turn red litmus blue, taste bitter, pH 7-14.

Theories:

• Arrhenius Theory: Acids release H+ ions, bases release OH- ions.
• Bronsted-Lowry Theory: Acids are proton donors, bases are proton acceptors.
• Lewis Theory: Acids accept electron pairs, bases donate electron pairs.

Conjugate Acids and Bases:

• Acids and bases form pairs that differ by one proton.
• Example: CH3COOH+H2O↔CH3COO−+H3O+
• Acid: CH3COOH, Conjugate base: CH3COO−
• Base: H2O, Conjugate acid: H3O+

Uses:

• Acids:

  • Vinegar for food preservation
  • Citric acid in lemon/orange juice
  • Sulphuric acid in batteries
  • Phosphoric acid in soft drinks

• Bases:

• • Sodium hydroxide in soap making
  • Calcium hydroxide in bleaching powder
  • Magnesium hydroxide as an antacid
  • Ammonium hydroxide in labs

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