pH and Brønsted-Lowry Theory
The Brønsted-Lowry theory offers another way to understand acids and bases. It defines an acid as a proton donor and a base as a proton acceptor. This helps explain reactions that the Arrhenius theory can't fully describe.
To identify acids and bases in this theory, look for conjugate pairs - substances that differ by one proton (H⁺). The acid always has one more hydrogen than its conjugate base. For example, HF (acid) and F⁻ (conjugate base) form a pair, with the acid having one more hydrogen.
The pH scale measures how acidic or basic a solution is, ranging from 0-14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic. This scale is logarithmic, meaning each whole number represents a tenfold change in acidity or alkalinity. A solution with pH 4 is ten times more acidic than pH 5!
The relationship between H⁺ and OH⁻ concentrations follows the equation H+OH− = 1.0 × 10⁻¹⁴ at 25°C. This means that as H⁺ concentration increases, pH decreases (more acidic), and as OH⁻ increases, pH increases (more basic).
📊 A useful shortcut: if you know the OH⁻ concentration (which gives you pOH), you can find pH by subtracting pOH from 14. For example, if OH− = 10⁻³, then pOH = 3 and pH = 14 - 3 = 11.