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Explore the fundamentals and practical applications of pH measurement in the laboratory setting. Learn about ionization of water, equilibrium constants, pH indicators, and various measurement tools like pH meters and electrodes.
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pH In the Laboratory Seidman & Moore pp. 380-383 Problems 1-5 page 400
Measuring pH • Indicater Dyes; Methyl Red, Phenol Red, etc. • pH Paper (Litmus Paper) • pH Meter
pH Meter • Voltmeter with electrode • Measures electrical potential difference across electrode due to protons • 1 pH unit = 60 mV • pH also dependent on temperature
pH Electrode • Filled with reference solution (4 M KCl, sat. AgCl) • Glass semi permable (protons cannot cross) • Glass protected by plastic sleeve • Some are sensitive to Tris buffer
pH Standards • Color coded 4, 7, and 10 • Potassium Hydrogen Pthalate • Standardize everyday • Bracket pH range
pH of Strong Acids • HCl <-> H+ +Cl- • Assume complete dissociation • 1 M HCl, pH = -log [H+] = -log 1 = ? • 0.5 M HCl, pH = -log 0.5 = ? • 6 M HCl, pH = -log 6 = ?
pH of Strong Bases • NaOH <-> Na+ + OH- • Assume complete dissociation • pKW = pH + pOH = 14 • pH = 14 – (-log [OH-]) • 1 M NaOH, pH = 14 – (-log 1) = ? • 0.01 M NaOH, pH = 14 – (-log 0.01) = ? • 6 M NaOH, pH = 14 – (-log 6) = ?
