Section outline

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      Important Terms:

      1. Acid is a substance that taste sour & turns blue litmus paper red.

      2. Base is a substance that taste bitter, feel soapy on touching & turns red litmus paper blue.

      3. Indicators are substances which help to test whether a substance is acidic or basic or neutral.

      4. Neutral solutions are those solutions which do not change the colour of either red or blue litmus

      5. Neutralisation is the reaction between acid & base to produce salt & water with evolution of heat.

      6. Acis rains is the rain containing excess of acids. 

      Key Points:

      1. Bases are soapy to touch.

      2. Acids release hydrogen ions in water.

      3. Base release hydroxide ions in water.

      4. Acids present in acid rain are carbonic acid, sulphuric acid and nitric acid.

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    • Quick Revision Notes:
      1. Indicator table:

      Natural Indicators:

      Indicator Acid Base
      Blue litmus  Red No change
      Red litmus No change Blue
      Turmeric No change Red
      China rose Magenta Green
      Purple cabbage  Red Green

      Chemical Indicators:

      Indicator Acid Base
      Methyl Orange Red Yellow
      Phenolphthalein  No change Pink

      **Indicators don't change colour in neutral solutions.

      2. Naturally occurring acids:
      Source of acid Acid
      Curd Lactic acid
       Spinach Oxalic acid
      Vinegar Acetic acid
      Ant’s sting Formic acid
      Tamarind, grapes, unripe mangoes, Tartaric acid
      Amla, Citrus fruits (oranges, lemons, etc.) Ascorbic acid (vitamin C)
      Citric acid

       

      3. Bases found in:
      Found in Base
      Lime water Calcium hydroxide 
      Window cleaner Ammonium hydroxide
       Soap Sodium hydroxide
      Potassium hydroxide
      Milk of magnesia (Antacid) Magnesium hydroxide

       

      4. Use of neutralisation reaction:
      Acid Base
      Indigestion (HCl acid) Antacid (milk of magnesia)
      Bee sting (formic acid) Baking soda
      (sodium hydrogencarbonate)
      Calamine solution 
      ( zinc carbonate)
      Acidic soil  Quick lime (calcium oxide) or
      Slaked lime (calcium hydroxide)
      Basic soil  Compost or organic matter
      Factory waste Treated with base.

       

      5. Acid Rains:
      • Air contains carbon dioxide, sulphur dioxide and nitrogen dioxide which are released as pollutants.
      • During the rainy season, these pollutants dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
      • This rain which contains excessive acids is called acid rain.
      • It damages historical buildings & monuments, plants & animals.