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Understanding pH in the Laboratory: Measurement and Applications

Explore the concept of pH in the laboratory setting, covering ionization of water, equilibrium constants like Keq and KW, acidity measurement using indicators and tools like pH paper and meter. Discover pH standards, electrode technologies, and calculations for strong acids, strong bases, and weak acids.

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Understanding pH in the Laboratory: Measurement and Applications

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  1. pH In the Laboratory

  2. Ionization of Water

  3. Equllibrium Constant, Keq

  4. Ion Product of Water, KW

  5. pH

  6. Acidity

  7. Measuring pH • Indicater Dyes; Methyl Red, Phenol Red, etc. • pH Paper (Litmus Paper) • pH Meter

  8. pH Meter • Voltmeter with electrode • Measures electrical potential difference across electrode due to protons • 1 pH unit = 60 mV • pH also dependent on temperature

  9. 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

  10. pH Standards • Color coded 4, 7, and 10 • Potassium Hydrogen Pthalate • Standardize everyday • Bracket pH range

  11. 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 = ?

  12. 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) = ?

  13. pH of a Weak Acid

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