acids, bases and salts

• Acids and Bases:

  • Acids have a sour taste and bases have a bitter taste
  • Acids change the colour of blue litmus to red
  • Bases change the colour of red litmus to blue
• Litmus is a natural indicator:

  • Purple in neutral solutions
  • Red in acidic solutions
  • Blue in basic solutions
• Turmeric is another natural indicator:

  • Turns reddish-brown in the presence of a base and yellow again when washed with water
• Acid-base indicators include:

  • Red cabbage leaves
  • Turmeric
  • Coloured petals of flowers like Hydrangea, Petunia, and Geranium
• Synthetic indicators for testing acids and bases:

  • Methyl orange
  • Phenolphthalein
• Olfactory indicators:

  • Some substances change odour in acidic or basic media
• Vanilla, onion, and clove can be used as olfactory indicators
• Reaction of metals with acids:

  • Acid + Metal → Salt + Hydrogen gas
• Reactions with metal carbonates and hydrogencarbonates:

  • Metal carbonate/Metal hydrogencarbonate + Acid → Salt + Carbon dioxide + Water
• Neutralisation reaction:

  • Base + Acid → Salt + Water
• Reaction of metallic oxides with acids:

  • Metal oxide + Acid → Salt + Water
• Reaction of a non-metallic oxide with base:

  • Carbon dioxide + Calcium hydroxide (lime water) → Calcium carbonate (white precipitate)
• Non-metallic oxides are acidic in nature
• Reaction between carbon dioxide and calcium hydroxide produces a salt and water
• All acids generate hydrogen gas on reacting with metals
• Acids contain H+ ion as cation and anion such as Cl- in HCl, NO3- in HNO3, SO42- in H2SO4, CH3COO- in CH3COOH
• Acids produce hydrogen ions, H+ (aq), in solution, which are responsible for their acidic properties
• Bases generate hydroxide (OH-) ions in water
• Acid + Base → Salt + Water
• Mixing an acid or base with water is a highly exothermic process
• The pH scale measures the acidic or basic nature of a solution, ranging from 0 (very acidic) to 14 (very alkaline)
• Values less than 7 on the pH scale represent an acidic solution, while values above 7 represent an alkaline solution
• Acids that give rise to more H+ ions are strong acids, and acids that give less H+ ions are weak acids
• Plants and animals work within the pH range of 7.0 to 7.8
• Living organisms can survive only in a narrow range of pH change
• When pH of rainwater is less than 5.6, it is called acid rain
• Acid rain lowers the pH of river water, making it difficult for aquatic life to survive
• Plants require a specific pH range for healthy growth
• Soil pH affects the growth of plants
• Stomach produces hydrochloric acid for digestion
• Excess stomach acid during indigestion causes pain and irritation
• Antacids neutralize excess stomach acid
• Tooth decay starts when the pH of the mouth is lower than 5.5
• Bacteria in the mouth produce acids causing tooth decay
• Using basic toothpaste can neutralize excess acid and prevent tooth decay
• Bee-sting leaves acid causing pain, relief can be provided by using a mild base like baking soda
• Nettle leaves inject methanoic acid causing burning pain
• Nettle sting can be relieved by using a mild base like baking soda
• Salts of a strong acid and a strong base are neutral with a pH value of 7
• Salts of a strong acid and weak base are acidic with a pH value less than 7