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Note on Bases

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Oxides of metals are called base. They are soapy to touch.

OR

Those compounds which release hydroxyl ion (Anion) in their aqueous solution are called base.

For e.g.

NaOH→Na+ + OH-

Ca(OH)2→ Ca+++ 2OH-

Mg(OH)2 → Mg++ + 2OH-

Alkali: Some metallic oxides (base) give their respective hydroxide when dissolved in water. Such water-soluble bases are called alkalis.

Types of base

On the basis of strength, bases are of two types:

  • Strong base: Those bases which go under complete ionization in aqueous solution and give the high concentration of hydroxyl ions are called strong bases.
  • Weak base: Those bases which go under partial ionization in aqueous solution and give low concentration of hydroxyl ions are called weak bases.

Similarly, on the basis of their origin, bases are of two types:

  • Organic bases: Those bases which are derived from living source are called organic bases.
  • Inorganic bases: Those bases which are obtained from minerals are called weak bases.

Properties of base

  1. Bases are bitter in taste and soapy feeling when touched.
  2. They turn red litmus into blue, colorless phenolphthalein into pink, methyl orange to light yellow.
  3. Base reacts with acid to give salt and water. NaOH(base) + HCl(acid)→NaCl(salt) + H2O(water)
  4. Alkalis react with carbon dioxide to produce carbonate salt and water. 2NaOH + CO2→Na2CO3 + H2O
  5. Alkalis react with ammonium salts on heating to produce ammonia gas. NH4Cl + NaOH→NH3+NaCl+ H2O

Uses of base

  • Caustic soda (NaOH) is used for the manufacture of soap, paper and rayon. It is also used in the refining of petroleum products.
  • Ammonium hydroxide is used for making chemical fertilizers.
  • Caustic potash is used in the manufacture of soft soaps.
  • Quick lime is used for softening hard water. It is also used in the manufacture of cement.

    http://www.plumbingconcepts.com/img/faq/hard_water.gif

    Fig: Formation of hard water

  • Those compounds which release hydroxyl ion (Anion) in their aqueous solution are called base.For e.g. NaOH → Na+ + OH+, Ca(OH)2 → Ca++ + 2OH+, Mg(OH)2 → Mg++ + 2OH-, etc.
  • Some metallic oxides (base) give their respective hydroxide when dissolved in water. Such water-soluble bases are called alkalis.
  • On the basis of strength, bases are divided as the strong base and weak base.
  • On the basis of their origin, bases are divided as the organic base and inorganic base.
  • Base reacts with acid to give salt and water.
  • Alkalis react with carbon dioxide to produce carbonate salt and water.
  • Alkalis react with ammonium salts on heating to produce ammonia gas.
  • Base is used to manufacture of soap, paper and rayon.
.

Very Short Questions

A base is a substance which gives hydroxyl ion (OH-) when dissolved in water.

Usually all bases or the oxide of metals are soluble in water but some bases like CuO, Fe2O3, etc. are not soluble in water. The bases which are soluble in water are called alkali. As all bases are not soluble in water, all alkalis are bases but all bases are not alkali.

The names of two antacids are as follows: a. Sodium hydrogen carbonate b. Mixture of aluminum hydroxides and magnesium hydroxides.

Calamine lotion or sodium hydrogen carbonate is used for the treatment for a nettle sting or ant-bite.

Copper sulphate is prepared by the reaction between an insoluble base and acid. At first, some copper oxide is added to dilute sulphuric acid. On warning, it dissolves and the solution turns blue. More copper oxide is added until no more dissolve. The excess of solid is removed by filtering. This leaves a blue solution of copper sulphate. The solution is heated to evaporate some of the water content. Then it is left to cool. Blue crystals of copper sulphate start to form.

When H2SO4 is dissolved in water, it gives (H+). Therefore, it is called acid. When NaOH is dissolved in water, it gives hydroxides ions (OH-). Therefore, this is called base.

Acetic acid gives less number of hydrogen ion (H+) in water. Therefore, it is called weak acid. When ammonia solution is ionized it gives less number of hydroxyl ion (OH-). Therefore, it is called weak alkali.

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  • Which of the following is known as a 'proton donor'?

    salt
    none of above
    Base
    Acid
  • Oxide of metals are called ______.

    salt


    amphoteric


    acid


    base


  • Which of the following is a weak base?

    NaOH
    NH4OH
    Ca(OH)2
    KOH
  • If _______ ions are found in a solution, the solution is basic in nature.

    hydronium


    hydroxyl


    hydrogen


    hydrogen and oxygen


  • The reaction of an acid with a base is called a ______.

    reversible reaction


    incomplete reaction


    complete  reaction


    neutralization reaction


  • Which is a soluble base in water?

    NaOH
    All the answers are correct
    Ca(OH)2
    KOH
  • Which one is the molecular formula of Sodium Hydroxide?

    Na2CO3
    NaOH
    NaCl
    NH4OH
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