Students will understand that pH and pOH measure the acidity and basicity of solutions. pH measures the concentration of hydrogen ions (H⁺), with values below 7 being acidic and above 7 being basic. pOH measures the concentration of hydroxide ions (OH⁻), with values below 7 being basic and above 7 being acidic. At 25°C, the sum of pH and pOH is always 14. This concept helps students relate acidity and basicity to ion concentration in aqueous solutions.