What is polyprotic acid ? Give examples of polyprotic acid and its ionization.
What is polyprotic acid ? Give examples of polyprotic acid and its ionization.
Polyprotic acid : The acids which have more than one ionizable proton per molecule of the acid. Such acids are known as polybasic or polyprotic acids.
Diprotic acid: The acid which have two ionizable proton per molecule of the acid. Such acids are known as Dibasic or Diprotic acid.
e.g., $\mathrm{H}_{2} \mathrm{X}+$ (aq) $+2 \mathrm{H}^{+}+\mathrm{X}^{2-} \quad \mathrm{K}_{a}$
The ionization of the reaction is in two steps is as under,
$(i)$ $\mathrm{H}_{2} \mathrm{X}+\mathrm{H}_{2} \mathrm{O}+\mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{HX}^{-} \quad \mathrm{K}_{a}$ $(i)$
$(ii)$ $\mathrm{HX}^{-}+\mathrm{H}_{2} \mathrm{O}+\mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{X}^{2-} \quad \mathrm{K}_{a}$ $(ii)$
In it, $\mathrm{K}_{a}$ $(i)$ $>\mathrm{K}_{a}$ $(ii)$ and $\mathrm{K}_{a}$ (i) $\times \mathrm{K}_{a}$ $(ii)$ $=\mathrm{K}_{a}$
Examples of diprotic acid : Oxalic acid $\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right)$, Sulphuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)$, Carbonic acid $\left(\mathrm{H}_{2} \mathrm{CO}_{3}\right)$, Sulphurous acid $\left(\mathrm{H}_{2} \mathrm{SO}_{3}\right)$, Ascorbic acid etc.
Examples of triprotic acid : Phosphoric acid $\left(\mathrm{H}_{3} \mathrm{PO}_{4}\right)$, Cytaric acid.... etc.
In polyprotic acid solution constant mixture of acid like $\mathrm{H}_{2} \mathrm{~A}, \mathrm{HA}^{-}$and $\mathrm{A}^{2-}$.
Similar Questions
Given
$(i)$ $\begin{gathered}
HCN\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons {H_3}{O^ + }\left( {aq} \right) + C{N^ - }\left( {aq} \right) \hfill \\
{K_a} = 6.2 \times {10^{ - 10}} \hfill \\
\end{gathered} $
$(ii)$ $\begin{gathered}
C{N^ - }\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons HCN\left( {aq} \right) + O{H^ - }\left( {aq} \right) \hfill \\
{K_b} = 1.6 \times {10^{ - 5}} \hfill \\
\end{gathered} $
These equilibria show the following order of the relative base strength
Given
$(i)$ $\begin{gathered}
HCN\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons {H_3}{O^ + }\left( {aq} \right) + C{N^ - }\left( {aq} \right) \hfill \\
{K_a} = 6.2 \times {10^{ - 10}} \hfill \\
\end{gathered} $
$(ii)$ $\begin{gathered}
C{N^ - }\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons HCN\left( {aq} \right) + O{H^ - }\left( {aq} \right) \hfill \\
{K_b} = 1.6 \times {10^{ - 5}} \hfill \\
\end{gathered} $
These equilibria show the following order of the relative base strength
- [AIEEE 2012]
When $100 \ mL$ of $1.0 \ M \ HCl$ was mixed with $100 \ mL$ of $1.0 \ M \ NaOH$ in an insulated beaker at constant pressure, a temperature increase of $5.7^{\circ} C$ was measured for the beaker and its contents (Expt. $1$). Because the enthalpy of neutralization of a strong acid with a strong base is a constant $\left(-57.0 \ kJ \ mol ^{-1}\right)$, this experiment could be used to measure the calorimeter constant. In a second experiment (Expt. $2$), $100 \ mL$ of $2.0 \ M$ acetic acid $\left(K_a=2.0 \times 10^{-5}\right)$ was mixed with $100 \ mL$ of $1.0 M \ NaOH$ (under identical conditions to Expt. $1$) where a temperature rise of $5.6^{\circ} C$ was measured.
(Consider heat capacity of all solutions as $4.2 J g ^{-1} K ^{-1}$ and density of all solutions as $1.0 \ g mL ^{-1}$ )
$1.$ Enthalpy of dissociation (in $kJ mol ^{-1}$ ) of acetic acid obtained from the Expt. $2$ is
$(A)$ $1.0$ $(B)$ $10.0$ $(C)$ $24.5$ $(D)$ $51.4$
$2.$ The $pH$ of the solution after Expt. $2$ is
$(A)$ $2.8$ $(B)$ $4.7$ $(C)$ $5.0$ $(D)$ $7.0$
Give the answer question $1$ and $2.$
When $100 \ mL$ of $1.0 \ M \ HCl$ was mixed with $100 \ mL$ of $1.0 \ M \ NaOH$ in an insulated beaker at constant pressure, a temperature increase of $5.7^{\circ} C$ was measured for the beaker and its contents (Expt. $1$). Because the enthalpy of neutralization of a strong acid with a strong base is a constant $\left(-57.0 \ kJ \ mol ^{-1}\right)$, this experiment could be used to measure the calorimeter constant. In a second experiment (Expt. $2$), $100 \ mL$ of $2.0 \ M$ acetic acid $\left(K_a=2.0 \times 10^{-5}\right)$ was mixed with $100 \ mL$ of $1.0 M \ NaOH$ (under identical conditions to Expt. $1$) where a temperature rise of $5.6^{\circ} C$ was measured.
(Consider heat capacity of all solutions as $4.2 J g ^{-1} K ^{-1}$ and density of all solutions as $1.0 \ g mL ^{-1}$ )
$1.$ Enthalpy of dissociation (in $kJ mol ^{-1}$ ) of acetic acid obtained from the Expt. $2$ is
$(A)$ $1.0$ $(B)$ $10.0$ $(C)$ $24.5$ $(D)$ $51.4$
$2.$ The $pH$ of the solution after Expt. $2$ is
$(A)$ $2.8$ $(B)$ $4.7$ $(C)$ $5.0$ $(D)$ $7.0$
Give the answer question $1$ and $2.$
- [IIT 2015]
Write examples of weak acids and weak bases and give ionic equilibrium in its aqueous solution.
Write examples of weak acids and weak bases and give ionic equilibrium in its aqueous solution.
The degree of dissociation of $0.1\,M\,HCN$ solution is $0.01\%$ . Its ionisation constant would be
The degree of dissociation of $0.1\,M\,HCN$ solution is $0.01\%$ . Its ionisation constant would be
The dissociation constant of an acid $HA$ is $1 \times {10^{ - 5}}$. The $pH$ of $0.1$ molar solution of the acid will be
The dissociation constant of an acid $HA$ is $1 \times {10^{ - 5}}$. The $pH$ of $0.1$ molar solution of the acid will be