The \(K_{\mathrm{w}}\) for \(2 \mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}+\mathrm{OH}^{-}\) changes from \(10^{-14}\) at \(25^{\circ} \mathrm{C}\) to \(9.62 \times 10^{-14}\) at \(60^{\circ} \mathrm{C} .\) What is \(\mathrm{pH}\) of water at \(60^{\circ} \mathrm{C} ?\) What happens to its neutrality?

The ion product of water, denoted as K_w, is essential in understanding the self-ionization of water. This constant represents the product of the molar concentrations of hydronium ions (H₃O⁺) and hydroxide ions (OH^-) in water. At 25°C, the value for K_w is well-known to be 10^-14. However, as temperature increases, so does the ion product. For instance, at 60°C, K_w becomes 9.62 x 10^-14. This increase suggests that water is more dissociated into its ions at higher temperatures, compared to room temperature.

In practical terms, knowing K_w at a specific temperature allows us to calculate the concentrations of hydronium and hydroxide ions in pure water, which is crucial for understanding pH and the acidic or basic nature of aqueous solutions at that temperature.

When water molecules split into ions, we see the emergence of hydronium ions, written as H₃O⁺. The concentration of these ions in water essentially determines the acidity of the solution. A high concentration implies a low pH, indicating an acidic solution, while a low concentration corresponds to a high pH, indicating a basic solution.

At different temperatures, H₃O⁺ concentration varies because the K_w changes. By assuming the molar concentration of hydronium ions is equal to that of hydroxide ions in pure water at a new temperature (like 60°C), we can calculate it by taking the square root of the K_w. This calculation directly reflects the fact that, as temperature changes, so does the balance point at which water is neither acidic nor basic.

pH is a measure of how acidic or basic water is, on a scale from 0 to 14, with 7 being neutral. It's defined as the negative logarithm of the hydronium ion concentration. To compute the pH of water or any aqueous solution, one essentially takes the negative base-10 logarithm of the H₃O⁺ concentration. As seen in the aforementioned exercise, this yields the pH of water at 60°C when we plug in the computed concentration of hydronium ions.

This relationship implies that even a slight deviation in H₃O⁺ concentration can result in a significant change in pH. Therefore, the pH calculation is a crucial tool for scientists and educators to indicate exactly how the acidity or basicity of water is affected by temperature.

Water's neutrality is a concept that revolves around its pH level being at 7, which is considered neutral. This occurs when the concentrations of hydronium and hydroxide ions are perfectly balanced, which is indeed the case at 25°C for pure water, with a K_w at this temperature being exactly 10^-14. However, this delicate balance gets disrupted as we change the temperature.

At higher temperatures like 60°C, the equilibrium shifts, leading to a change in the ion product of water. Consequently, even though the concentration of hydronium equals that of hydroxide ions, the pH deviates from 7, indicating that water is no longer neutral under these conditions. This reality is of particular importance in chemical reactions and processes where maintaining a strict pH is vital, such as in biological systems and industrial applications.