Question

Pure water does not conduct electricity because it is_____?

• A. Neutral
• B. Almost Unionized
• C. Completely Unionized
• D. Readily Decomposed.

Answer 1

The correct option is B

Almost Unionized

Explanation for Correct answer:-

Option (B): Almost Unionized

• Electrical conductivity generally occurs due to the free ions present in the solution.
• The mineral ions, protons, and hydroxide ions are majorly responsible for the conductance of electricity.
• Pure water is almost unionized and therefore its electrical conductivity is very low.
• Water undergoes self-ionize to a very small extent under normal conditions, which can be shown as:

$2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\leftrightarrows {\mathrm{H}}_3{\mathrm{O}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{–}\left(\mathrm{aq}\right)$

• Where Dissociation constant is given as:${\mathrm{K}}_{\mathrm{w}}=\frac{[\mathrm{H}+][\mathrm{OH}-]}{{\left[{\mathrm{H}}_2\mathrm{O}\right]}^2}$
• The value of the Ionic product or Dissociation constant of water depends on the product of the molar concentration of ${\mathrm{H}}^{+}\mathrm{and}{\mathrm{OH}}^{-}$ions, which is given by:
  $$\begin{gathered} \mathrm{Kw}=[\mathrm{H}+][\mathrm{OH}-]={10}^{-14} \\ \mathrm{K}=\frac{55.55}{{10}^{-14}}=1.8\times {10}^{-16} \end{gathered}$$
• As the dissociation constant value of pure water is very small, hence, the number of ${\mathrm{H}}^{+}\mathrm{and}{\mathrm{OH}}^{-}$ions undergoing dissociation is also very negligible, which explains the reason why Pure water does not conduct electricity.
  

Explanation for Incorrect answer:

Option (A)

• Unionizable water with no impurities cannot conduct electricity as there are no charge carriers to carry the electricity.
• Neutral water still has some dissolved ions that are responsible for the conduction of electricity.
• Therefore, this option is incorrect.

Option (C)

• Every solution has some ionization constant that indicates that all solutions are ionizable.
• Therefore, this option is incorrect.

Options (D)

• Pure water does not decompose.
• Therefore, this option is incorrect.

Therefore, pure water does not conduct electricity because it is almost unionized.