Salt formation takes place only by reacting an appropriate acid and a base which are sufficiently acidic or basic, respectively, to react completely. This point may be made clear by taking this example, Thus if we desire to prepare the sodium salt of urea, [Na⁺ (H₂NCONH^-)]. we must employ a base which is strong enough to be able to take away a proton form the very weakly acidic urea molecule. The strongest base which can exist in water, the hydroxide ion, OH^- is not capable of taking a proton form the urea molecule. The salt Na⁺ (H₂NCONH^-) cannot be prepared in aqueous solution or in other words we may say that the equilibrium in the reaction

Na⁺ (H₂NCONH^-)  +  H₂O   →     NaOH  +  H₂NCONH₂          

lies to the right.

This salt may, however, be prepared in liquid NH₃ by the reaction between urea and the strong base sodium amide.

H₂NCONH₂ + Na⁺NH₂^-  →    Na⁺(H₂NCONH^-)  + NH₃

Another interesting example may be the isolation of a salt of nitronium ion, NO₂⁺CIO₄^-. Nitronium ion is highly electrophilic and is unstable in the basic aqueous medium. This compound may be isolated in liquid SO₂ highly acidic 100% sulphuric acid.

For more help in Salt Formation click the button below to submit your homework assignment