Question

Carbonic acid is a polyprotic acid. write balanced chemical equations for the sequence of reactions that carbonic acid can undergo when it's dissolved in water.

Answer 1

Carbonic acid (H₂CO₃) dissociation in water takes place in 2 steps. its a polypro tic acid as it has 2 H⁺ ions it can donate.
the dissociation reactions in water are as follows;
H₂CO₃  + H₂O ---> HCO₃⁻ + H₃O⁺
in the first dissociation it releases a proton that combines with water to form a hydronium ion.
HCO₃⁻ + H₂O  ----> CO₃²⁻ + H₃O⁺
second dissociation results in the carbonate ion and hydronium ion formation.
As the ratio of acid dissociation constant ka1/ka2 > 10⁴ , dissociation takes place in 2 steps. 

Answer 2

The sequence of dissociation reactions of carbonic acid is a follows:

 $\text{Step\;1:\;}\text{H}_2\text{CO}_3(aq)+\text{H}_2\text{O}(aq)\overset{\text{K}_{al}}\leftrightharpoons\text{HCO}_3^-(aq)+\text{H}_3\text{O}^+(aq)\\\text{Step\;2:\;}\text{H}_2\text{CO}_3^-(aq)+\text{H}_2\text{O}(aq)\overset{\text{K}_{al}}\leftrightharpoons\text{CO}_3^2\;(aq)+\text{H}_3\text{O}^+(aq)$

Further Explanation:

An acid is a substance that is able to donate a proton or hydrogen ion $\left( {{{\text{H}}^ + }} \right)$ in aqueous solutions. Hydrochloric acid (HCl), sulphuric acid $\left( {{{\text{H}}_2}{\text{S}}{{\text{O}}_4}} \right)$ and nitric acid $\left( {{\text{HN}}{{\text{O}}_3}} \right)$ are some examples of acids. On the basis of the number of protons an acid can donate, acids can be monoprotic or polyprotic.

Acids that can donate just one proton in aqueous solutions are called monoprotic acids. For example, HCl, ${\text{HN}}{{\text{O}}_{\text{3}}}$ and ${\text{C}}{{\text{H}}_3}{\text{COOH}}$ are monoprotic acids as these can donate only one proton in solutions.

Polyprotic acids can donate more than one proton in aqueous solutions. These can further be divided as diprotic, triprotic and so on. Diprotic acids are the ones that can donate two protons in solutions. For example, ${{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$ and ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$ are diprotic acids. Triprotic acids are capable to donate three protons in solutions. For example, ${{\text{H}}_{\text{3}}}{\text{As}}{{\text{O}}_{\text{4}}}$ and ${{\text{H}}_3}{\text{P}}{{\text{O}}_4}$ are triprotic acids.

Carbonic acid has the chemical formula of ${{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$. So it dissociates into an aqueous solution, releasing protons or hydrogen ions in it. Since carbonic acid is a diprotic acid, its dissociation takes place in two steps.

Step 1: The first dissociation of ${{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$ occurs as follows:

 $\text{H}_2\text{CO}_3(aq)+\text{H}_2\text{O}(aq)\overset{\text{K}_{al}}\leftrightharpoons\text{HCO}_3^-(aq)+\text{H}_3\text{O}^+(aq)$

Here, $K_a_1$ is the first dissociation constant of ${{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$.

Step 2: In the second dissociation, ${\text{HCO}}_3^ -$ dissociates as follows:

 $\text{H}_2\text{CO}_3^-(aq)+\text{H}_2\text{O}(aq)\overset{\text{K}_{al}}\leftrightharpoons\text{CO}_3^2\;(aq)+\text{H}_3\text{O}^+(aq)$

Here, ${K_{{\text{a2}}}}$ is the first dissociation constant of ${{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$.

Learn more:

1. The reason for the acidity of water brainly.com/question/1550328
2. Reason for the acidic and basic nature of amino acid. brainly.com/question/5050077

Answer details:

Grade: High School

Chapter: Acid, base and salts.

Subject: Chemistry

Keywords: acids, monoprotic, polyprotic, HCl, H2CO3, H2SO4, HNO3, CH3COOH, dissociation, Ka1, Ka2.