Tuesday, September 6, 2011

Solutions and Suspensions : Acids and Alkalis


  1. Solution is a homogeneous mixture of two or more substances.
  2. Solute is the substance that dissolves in a solvent to form a solution.
  3. Solvent is the substance in which the solute dissolves to form a solution.
  4. We come across many type of solutions in our daily life. Generally the term solution is understood with relation to liquids. But, the solvent can be a solid, liquid or gas which can dissolve one or more substances (solutes) to form a solution. The combination is of various types like solid-solid, solid-liquid, solid-gas, liquid-liquid, liquid-gas and gas-gas etc. are examples of solute-solvent combination to form a solution.
  5. Example of solid-solid are alloys like brass (solute zinc in copper)
    Example of solid-liquid is sugar in water (solute sugar in water)
    Example of gas-liquid are carbonated drinks (solute carbon dioxide in water)
  6. Water is called the universal solvent. We cannot imagine a life on earth without water. The main reasons for considering water as an universal solvent is,
         (i) Due to its polar nature it dissolves many ionic compounds.
         (ii) The hydrogen atoms of water form loose hydrogen bonds which help in dissolving many covalent
              compounds.
         (iii) Water undergoes chemical combination with many compounds resulting in their dissolution.
  7. Suspension is a mixture in which small solid orwhich  liquid particles are suspended in a liquid or gas.
  8. Solubility: The maximum amount of solute which can dissolve in 100g of the solvent is known as the solubility of that solute in that solvent at that given temperature. Solubility is influenced by (i) the nature of the solute, (ii) the nature of the solvent and (iii) the temperature of the solution.

    The solubility of solids in liquids usually increases with increasing temperature.
    The solubility of gases in liquids usually decreases with increasing temperature.
  9. Strength of solutions:
    Dilute or weak solutions:
    When the concentration of the solute is less compared to the amount of solvent.
    Concentrated or strong solutions: When a large amount of solute is dissolved in a small amount of solvent.
    Saturated solutions: A solution in which no more solute can be dissolved at the given temperature.
    Unsaturated solution: A solution in which more solute can be dissolved at the given temperature.
  10. Some of the uses of solutions and solvents.
    At home
      -
    Water is the most important solvent used in cooking, cleaning, washing etc. Other solvents like
        turpentine, petrol are used to remove grease. Acetone is used in removing the nail polish applied to
        nails.
    In industries
      - Apart from water, which is used in food, beverage, detergent, dye and other industries, most
        solvents used in industries are organic in nature, Ethanol is used in perfume industry, Acetone,
        benzene, ether are other solvents used industrially.
    In agriculture
      - Water is the important solvent in agriculture. Minerals, fertilizers and other nutrients reach the plant
        only due to the solubility of these in water. Organic solvents are used in pesticides and insecticides.
    In medicine
      - All the syrups and decoctions used in medicines are solutions. Water again serves an an important
        solvent for many of the herbal medicines. Some vitamins are water soluble, which others are fat
        soluble.
  11. Colloidal solutions: A solution is which the size of the solute particles are between that of the solution and suspension. eg. milk, blood
      - The size of a colloidal particle is between 10 to the power of -7 and 10 to the power of -5.
      - The particles of a colloid can pass through filter paper.
      - The solution here is translucent.
      - It scatters light which makes its path visible.
  12. Acids
    Acids are those compounds that contain hydrogen and can donate the H+ ions.The basic properties of acids are:
      - they have a sour taste.
      - they turn blue litmus red.
      - they are corrosive in nature.
      - they react with alkalis to give salt and water.
      - they react with carbonates to give CO2.
      - they react with active metals to produce H2 gas.
  13. The some of the common acids and their uses.
    Hydrochloric acid:  - found in the stomach and helps in digestion of food.
                                  - used in cleaning.
    Nitric acid:  - used in the preparation of fertilizers like ammonia.
                       - used in the preparation of explosives.
    Sulfuric acid:  - used in car batteries.
                         - used in the preparation of fibers and plastics.
    Carbonic acid:  - used in making carbonated drinks.
                            - helps in the pH balance of the biological systems.
    Ethanoic acid:  - used in the preservation of food stuffs.
  14. AlkalisAlkalis are bases when dissolved in water yields hydroxide ions (OH- ions). The basic properties of alkalis are:
      - they are bitter to taste and have a soapy feel.
      - they turn red litmus blue.
      - generally corrosive in nature in concentrated form.
      - they are good conductors of electricity.
      - they react with acids to form salt and water.
      - the react with ammonium salts to produce ammonia gas.
  15. Some of the common alkalis and their uses 
    Potassium hydroxide:  - used in dyeing.
                                      - used to remove paint and varnish.
    Sodium hydroxide:  - used in the preparation of soaps.
    Ammonia solution:  - used to make fertilizers.
                                  - used in the preparation of cleaning liquids.
    Calcium hydroxide:  - used to adjust the pH of acidic soil.

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