pII of water is 7 at 25^∘ C. If water is heated to 70^∘ C the (1) pII will decrease and solution

step 1 Dear students, in problem 29 of chapter 7, we have asked that pH of water is 7 at 25 degree. If

PII of water is 7 at 25^∘ C. If water is heated to 70^∘ C...

pII of water is 7 at $25^{\circ} \mathrm{C}$. If water is heated to $70^{\circ} \mathrm{C}$ the (1) pII will decrease and solution becomes acidic (2) pII will increasc and solution becomes basic (3) pII will remain constant and solution is neutral (4) pII will decrease but solution will be neutral

pII of water is 7 at $25^{\circ} \mathrm{C}$. If water is heated to $70^{\circ} \mathrm{C}$ the
(1) pII will decrease and solution becomes acidic
(2) pII will increasc and solution becomes basic
(3) pII will remain constant and solution is neutral
(4) pII will decrease but solution will be neutral

Key Concepts

Ion Product of Water (Kw)

The ion product of water, Kw, is the equilibrium constant for the self-ionization of water into hydrogen ions (H+) and hydroxide ions (OH-). It is defined by the product [H+][OH-] and is temperature-dependent, meaning that its value changes as the temperature of the water changes. At 25°C, Kw is typically around 1.0 × 10?¹?, which leads to a neutral pH of 7.

Temperature Dependence of Equilibrium Constants

Equilibrium constants, including Kw for the autoionization of water, are sensitive to temperature changes. As temperature increases, the equilibrium for many reactions shifts, altering the concentrations of products and reactants. For water, an increase in temperature results in an increased Kw because the endothermic nature of the ionization allows more water molecules to dissociate.

Concept of pH and pOH

pH is a measure of the hydrogen ion concentration in a solution, defined as the negative logarithm of the hydrogen ion concentration. Similarly, pOH is defined for hydroxide ions. In pure water, where [H+] equals [OH-], the pH is half of the pKw, meaning that any change in Kw due to temperature changes will also alter the pH and pOH values. However, this change in numerical pH does not indicate the solution has become acidic or basic on its own.

Neutrality in Pure Water

Neutrality in a solution, particularly in pure water, is defined as having equal concentrations of hydrogen ions and hydroxide ions. Even though the numerical value of pH changes with temperature due to the changing ion product (Kw), pure water remains neutral because the ratio of H+ to OH- stays equal. Thus, a decrease in pH at higher temperatures does not mean the water has become acidic; it simply reflects the altered equilibrium conditions.

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