What is pH and how is it measured?

pH measures the acidity or alkalinity of a solution on a scale of 0-14, where 7 is neutral, below 7 is acidic, and above 7 is alkaline. pH is measured using a glass electrode that develops voltage proportional to hydrogen ion concentration when compared to a reference electrode. The relationship is logarithmic - each pH unit represents a 10-fold change in H+ concentration. pH meters convert the millivolt signal to pH units using the Nernst equation.