Question

Choose strong acid and strong base from the following:
$ {\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH, N}}{{\text{H}}_{\text{4}}}{\text{OH, KOH, HCl}}$

Answer 1

Hint: To answer this question, you must recall the Arrhenius concept of acids and bases. The strength of an acid or base depends upon its ability to dissociate in water. A strong acid and a strong base is that which can dissociate completely in water.

Complete step by step solution:
First we check the strong acid of the given acids. We know that strong acids are those acids which ionize or dissociate completely in an aqueous solution. Acids dissociate in water to give a proton or a hydronium ion $ \left( {{{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}} \right) $ and a conjugate base. Since it dissociates completely in water, a strong acid gives $ 100\% $ of $ {{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}} $ ions. We know that $ {\text{HCl}} $ dissociates completely in its aqueous solution to give chloride ion and hydronium ion and thus, it is a strong acid. On the other hand, acetic acid $ \left( {{\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH}}} \right) $ does not undergo complete dissociation and is a weak acid.
Similarly, strong bases are those bases which ionize or dissociate completely in an aqueous solution. Bases dissociate in water to give a hydroxide ion $ \left( {{\text{O}}{{\text{H}}^ - }} \right) $ and a conjugate acid. Since it dissociates completely, a strong base will give $ 100\% $ of $ {\text{O}}{{\text{H}}^ - } $ ions. We know that potassium hydroxide $ \left( {{\text{KOH}}} \right) $ dissociates completely in its aqueous solution into potassium ion and hydroxide ion. Thus, it is a strong base. On the other hand, ammonium hydroxide does not undergo complete dissociation and is a weak base.
The correct answer is $ {\text{HCl}} $ and $ {\text{KOH}} $ .

Note:
We define a substance as acidic and basic relative to water, Thus water is considered as neutral in nature. Also, strong acids are strong acids only when they dissociate significantly in aqueous solution. If the amount of water in the solution is less, the acid does not dissociate much. Similar is the case for bases.