For pure water : (a) pH increases while pOH decreases with...

For pure water :
(a) $\mathrm{pH}$ increases while pOH decreases with rise in temperature
(b) pH decreases while pOH increases with rise in temperature
(c) both $\mathrm{pH}$ and pOH decreases with rise in temperature
(d) both $\mathrm{pH}$ and pOH increases with rise in temperature

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Key Concepts

Autoionization of Water

This concept refers to the process in which water molecules spontaneously dissociate into hydrogen ions (H?) and hydroxide ions (OH?). The extent of this dissociation is quantified by the ion-product constant for water (Kw). Understanding autoionization is crucial because it explains the presence of ions in pure water and forms the basis for pH measurements.

pH and pOH

pH is a measure of the acidity of a solution, defined as the negative logarithm of the hydrogen ion concentration, while pOH is similarly defined for the hydroxide ion concentration. In water, these values are interrelated through the relationship pH + pOH = -log(Kw). This concept is fundamental in acid-base chemistry and helps in understanding how changes in ion concentration affect the solution's overall acidity or basicity.

Temperature Dependence of Equilibrium Constant

The equilibrium constant for autoionization of water (Kw) is temperature-dependent, increasing as the temperature rises. This means that at higher temperatures, greater concentrations of H? and OH? ions are produced, leading to a decrease in both pH and pOH in pure water. This concept illustrates how temperature can influence chemical equilibria and the properties of solutions.

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