What is the value of the water autoionization constant (Kw) at 25°C?

The water autoionization constant, commonly represented as ( K_w ), is a fundamental constant that reflects the dissociation of water into hydrogen ions ((H^+)) and hydroxide ions ((OH^-)). At a temperature of 25°C, the value of ( K_w ) is defined to be ( 1 \times 10^{-14} ).

This constant is crucial in various calculations relating to pH, acidity, and basicity in aqueous solutions, as it directly connects to the concentrations of ( H^+ ) and ( OH^- ) ions in water. Specifically, the relationship can be expressed as ( K_w = [H^+][OH^-] ). Since pure water at 25°C has equal concentrations of ( H^+ ) and ( OH^- ), each roughly equals ( 1 \times 10^{-7} ) M, leading to the product giving the defined value of ( K_w ).

This understanding of ( K_w ) and its importance in the context of acid-base chemistry is vital for grasping various biological and chemical processes, as well as for solving related problems on the MCAT.