Question

Define acids and bases according to Bronsted-Lowry theory. Derive the relationship between pH and pOH.

Hint:

The pH and pOH of a solution are related by (pH + pOH = 14), a relationship that holds true for aqueous solutions at 25°C.

Answer 1

Bronsted-Lowry Definition:

• Acids: Substances that donate protons \( (H^+) \).
• Bases: Substances that accept protons \( (H^+) \).

Example: \[ NH_3 + H_2O \rightleftharpoons NH_4^+ + OH^- \] In this reaction, \( NH_3 \) acts as a Bronsted base (accepting a proton), while \( H_2O \) serves as a Bronsted acid (donating a proton). 
Relationship Between pH and pOH: We know the following equations: \[ pH = -\log [H^+] \] \[ pOH = -\log [OH^-] \] Also, it holds that: \[ [H^+] [OH^-] = 10^{-14} \] Taking the logarithm of both sides: \[ pH + pOH = 14 \]