Understanding the Difference Between Strong and Weak Acids

The chemical formulae of some acids are listed in the first column of the table below, and in the second column it states whether each acid is strong or weak.

Complete the table. List the chemical formula of each species present at concentrations greater than about [tex][tex]$10^{-6}$[/tex][/tex] mol/L when about a tenth of a mole of the acid is dissolved in a liter of water.

\begin{tabular}{|c|c|c|}
\hline
acid & \begin{tabular}{c}
strong or \\
weak?
\end{tabular} & \begin{tabular}{c}
species present at [tex][tex]$10^{-6}$[/tex][/tex] mol/L or greater \\
when dissolved in water
\end{tabular} \\
\hline
[tex]HIO_3[/tex] & strong & [tex]$\square$[/tex] \\
\hline
[tex]H_2S[/tex] & weak & [tex]$\square$[/tex] \\
\hline
[tex]H_2SO_3[/tex] & weak & [tex]$\square$[/tex] \\
\hline
[tex]HI[/tex] & strong & [tex]$\square$[/tex] \\
\hline
\end{tabular}



Answer :

To complete the table, we need to identify each acid as either strong or weak and list the species present at concentrations greater than [tex]\(10^{-6}\)[/tex] mol/L when approximately a tenth of a mole of the acid is dissolved in a liter of water.

Here’s the detailed solution:

1. HIO[tex]\(_3\)[/tex] (Iodic acid)
- Strong or Weak?: Strong Acid
- Explanation: Strong acids dissociate completely in water.
- Dissociation: [tex]\( \text{HIO}_3 \rightarrow \text{H}^+ + \text{IO}_3^- \)[/tex]
- Species present:
- HIO[tex]\(_3\)[/tex] (remaining undissociated)
- H[tex]\(^+\)[/tex]
- IO[tex]\(_3^-\)[/tex]

2. H[tex]\(_2\)[/tex]S (Hydrosulfuric acid or Hydrogen sulfide)
- Strong or Weak?: Weak Acid
- Explanation: Weak acids only partially dissociate in water.
- Dissociation: [tex]\( \text{H}_2\text{S} \rightleftharpoons \text{H}^+ + \text{HS}^- \rightleftharpoons \text{H}^+ + \text{S}^{2-} \)[/tex]
- Species present:
- H[tex]\(_2\)[/tex]S
- H[tex]\(^+\)[/tex]
- HS[tex]\(^{-}\)[/tex]
- S[tex]\(^2{}^{-}\)[/tex]

3. H[tex]\(_2\)[/tex]SO[tex]\(_3\)[/tex] (Sulfurous acid)
- Strong or Weak?: Weak Acid
- Explanation: Weak acids only partially dissociate in water.
- Dissociation: [tex]\( \text{H}_2\text{SO}_3 \rightleftharpoons \text{H}^+ + \text{HSO}_3^- \rightleftharpoons \text{H}^+ + \text{SO}_3^{2-} \)[/tex]
- Species present:
- H[tex]\(_2\)[/tex]SO[tex]\(_3\)[/tex]
- H[tex]\(^+\)[/tex]
- HSO[tex]\(_3^-\)[/tex]
- SO[tex]\(_3^{2-}\)[/tex]

4. HI (Hydroiodic acid)
- Strong or Weak?: Strong Acid
- Explanation: Strong acids dissociate completely in water.
- Dissociation: [tex]\( \text{HI} \rightarrow \text{H}^+ + \text{I}^- \)[/tex]
- Species present:
- HI (remaining undissociated)
- H[tex]\(^+\)[/tex]
- I[tex]\(^{-}\)[/tex]

Now, we can fill in the table:

\begin{tabular}{|c|c|c|}
\hline
acid & \begin{tabular}{c}
strong or \\
weak?
\end{tabular} & \begin{tabular}{c}
species present at [tex]$10^{-6}$[/tex] mol/L or greater \\
when dissolved in water
\end{tabular} \\
\hline
HIO[tex]\(_3\)[/tex] & strong & HIO[tex]\(_3\)[/tex], H[tex]\(^+\)[/tex], IO[tex]\(_3^{-}\)[/tex] \\
\hline
H[tex]\(_2\)[/tex]S & weak & H[tex]\(_2\)[/tex]S, H[tex]\(^+\)[/tex], HS[tex]\(^-\)[/tex], S[tex]\(^2{}^{-}\)[/tex] \\
\hline
H[tex]\(_2\)[/tex]SO[tex]\(_3\)[/tex] & weak & H[tex]\(_2\)[/tex]SO[tex]\(_3\)[/tex], H[tex]\(^+\)[/tex], HSO[tex]\(_3^{-}\)[/tex], SO[tex]\(_3^{2-}\)[/tex] \\
\hline
HI & strong & HI, H[tex]\(^+\)[/tex], I[tex]\(^{-}\)[/tex] \\
\hline
\end{tabular}

This table now correctly lists each acid as strong or weak and enumerates the species present at significant concentrations when dissolved in water.