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Home » Class 11 » Chemistry » Ionic Equilibrium » Dissociation Constant and Ionic Product of Water

Dissociation Constant and Ionic Product of Water

Last Updated on February 16, 2023 By Mrs Shilpi Nagpal

Pure water is poor conductor of electricity.

Water is a weak electrolyte i.e. it is ionized to a very small extent as:

H2O sign of equilibrium reaction H+ + OH‾

H2O + H2O sign of equilibrium reaction H3O+ + OH‾

This ionization is called self ionization of water.

Equilibrium constant for water

where Keq is the dissociation constant of water.

Ionic product of water

Kw is the ionic product of water.

Ionic product of water may be defined as the product of the molar concentration of H+ ions and OH‾ ions.

As H+ ions in water exist as H3O+ ions, therefore, ionic product may also be defined as the product of molar concentration of H3O+ ions and OH‾ ions, i.e.

ionic product

OR

ionic products

Ionic product of water is constant only at constant temperature.

Kw at 298 K

Kw = 1.00 × 10-14

Dissociation or ionization of constant of water is different from ionic product of water.

Keq = Kw / 55.55

Kw = Keq × 55.55

Keq = 10-14 /55.55 = 1.8 × 10-16

In pure water

Pure water

Ionic product of pure water

Effect of temperature on Kw

The ionic product of water increases with increase of temperature.

With increase of temperature ,the degree of ionization of water increases. More of water molecule dissociate into H+ ions and OH‾ ions.The concentration of H+ and OH‾ ions increases and hence the ionic product also increases.

H3O+ ion and OH‾ ion concentration in aqueous solution of acid and bases

Pure water

If some acid is added to pure water, then ( H3O+ ) > 10-7M

conc of hydroxide ion = Kw / conc of hydrogen

If some base is added to pure water, then conc of hydroxide ion  = 10-7 M

conc of hydronium ion = Kw / conc of hydroxide ion

The increase or decrease of the H3O+ ion concentration in an aqueous solution of an acid or a base may be explained qualitatively on the basis of Le Chatelier’s principle.

2H2O sign of equilibrium reactionH3O+ + OH‾

If some acid is added to pure water, H3O+ ion concentration increases , therefore the equilibrium shifts in the backward direction.Thus OH‾ ion concentration decreases.

If a base added, OH‾ concentration increases.Again the equilibrium shifts in the backward direction and hence the H3O+  ion concentration decreases.

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Filed Under: Chemistry, Class 11, Ionic Equilibrium Tagged With: Dissociation or ionization of constant of water, Effect of temperature on Kw, H3O+ ion and OH‾ ion concentration in aqueous solution of acid and bases, ionic product of water, self ionization of water

Reader Interactions

Comments

  1. Murali Krishna says

    January 13, 2019 at 7:01 pm

    I am very much impressed by the way ionic product is explained. Now I am satisfied and have cleared my doubts.
    Thanks

  2. Sinu says

    February 3, 2019 at 8:26 pm

    Nice

  3. indu bala says

    July 5, 2020 at 9:47 pm

    thank you

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