Acids, Bases, and Salts Chapter 2

Acids, Bases, and Salts

• Acids are sour in taste and change the color of blue litmus to red.
• Bases are bitter and change the color of red litmus to blue.
• Litmus is a natural indicator, which can be used to test for acids and bases.

Indicators

• Litmus solution is a purple dye extracted from lichen, a plant belonging to the division Thallophyta.
• Litmus solution turns:
  • Red in acidic solutions
  • Blue in basic solutions
  • Purple in neutral solutions (neither acidic nor basic)
• Other natural indicators include:
  • Red cabbage leaves
  • Turmeric
  • Colored petals of some flowers (e.g., Hydrangea, Petunia, and Geranium)

Identifying Acids and Bases Using Litmus Paper

• To identify the contents of three test tubes containing distilled water, an acidic solution, and a basic solution, using only red litmus paper:
  • Observe the color change of the red litmus paper in each test tube.
  • If the paper turns blue, the solution is basic.
  • If the paper remains red, the solution is acidic or neutral (distilled water).

Chemical Properties of Acids and Bases

Laboratory Acids

• Three common acids found in the laboratory are:
  • Hydrochloric acid (HCl)
  • Sulphuric acid (H₂SO₄)
  • Nitric acid (HNO₃)