Q. Is \( \text{H}_2\text{O} \) a weak base?

To decide whether \(\mathrm{H_2O}\) is a weak base, we need to look at how water behaves in water and what particles it can produce.

Step 1: Recall what a “base” does

A base is a substance that can accept a proton \(\mathrm{H^+}\) (or, equivalently, produce hydroxide \(\mathrm{OH^-}\) in water).

Step 2: Use the equilibrium for water self-ionization

Water can react with itself very slightly:

\[
\mathrm{2H_2O \rightleftharpoons H_3O^+ + OH^-}
\]

This shows that water can produce both \(\mathrm{H_3O^+}\) and \(\mathrm{OH^-}\). Because it can generate \(\mathrm{OH^-}\), water has basic behavior.

Step 3: Decide whether the basic behavior is “weak”

The key point is that this ionization happens only to a very small extent.

In pure water at \(25^\circ\mathrm{C}\), the concentration of \(\mathrm{OH^-}\) is extremely small:

\[
[\mathrm{OH^-}] = 1.0 \times 10^{-7}\ \mathrm{M}
\]

That very low value indicates that water does not strongly create \(\mathrm{OH^-}\). Therefore, its basic strength is weak.

Step 4: State the conclusion

Yes. \(\mathrm{H_2O}\) is considered a weak base because it only slightly accepts protons (producing a small amount of \(\mathrm{OH^-}\)) through self-ionization.

Extra clarity (optional but helpful): Water is also a weak acid and a weak base, so it is often described as amphoteric.