• Some naturally occuring acids

       Vinegar – Acetic Acid

        Orange – Citric Acid

        Lemon – Citric Acid

       Tamarind – Tartaric Acid

       Tomato – Oxalic Acid

       Sour milk (Curd) – Lactic Acid

      Ant and Nettle sting – Methanoic Acid

• Acid – Base Indicators – Indicate the presence of an acid or base in a solution.

• Litmus solution – It is a natural indicator. It is a purple dye extracted from Lichens. Other examples are Red Cabbage and coloured petals of Petunia and turmeric.

• Olfactory indicators – Show odour changes in acidic or basic media.

      eg. onion and clove.

• Acid – Base Indicators

     

• Dilute Acid : Contains only a small amounts of acid and a large amount of water.

• Concentrated Acid : A concentrated acid contains a large amount of acid and a small amount of water.

• Chemical Properties of Acids and Bases

(i) Reaction with metal

     Acid + Metal → Salt + Hydrogen

    2HCl + Zn → ZnCl₂ + H₂

    2HNO₃ + Zn → Zn (NO₃)₂ + H₂

    H₂SO₄ + Zn → ZnSO₄ + H₂

   2CH₃COOH + Zn → (CH₃COO)₂ Zn + H₂

• Pop test : When a burning candle is brought near a test tube containing hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining the presence of hydrogen gas.

• Base + Metal → Salt + Hydrogen

      NaOH + Zn → Na₂ZnO₂ + H₂
                             Sodium Zincate

     Note – Such reactions are not possible with all the metals.

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