Chemistry · MU Plovdiv

3. Self-ionization of water, ionic product of water. The pH scale, methods of measuring pH. Buffers – definition, buffer action. Calculation of the pH of buffers – Henderson-Hasselbalch’s equations. Buffers in the human body.

Inside: 15 sections · 13 labelled pictures · 39 flashcards · 12 min

Topic 3 of 26 in the MU Plovdiv syllabus for Chemistry (Medicine, Year 1). The free AceMed note covers it in 15 sections, about 1,693 words (12 min of reading), with 39 flashcards.

In this note

  1. Autoproteolysis.
  2. Ion product constant of water.
  3. pH concept (рН).
  4. Importance of pH homeostasis in body fluids.
  5. Methods for pH measurement and biological significance.
  6. Autoprotolysis, Ion Product of Water, and pH
  7. Autoprotolysis (Self-Ionization)
  8. pH Concept
  9. Biological pH Homeostasis
  10. Introduction
  11. Buffer solutions – definition, properties.
  12. Henderson - Hasselbalch equation.
  13. Buffer capacity (β)
  14. Preparing a buffer solution with a specific pH.
  15. Buffers: The Key to Life-Sustaining Blood pH

Autoproteolysis.

  • Autoprotolysis is a type of chemical reaction occurring in amphiprotic solvents, where two molecules of the solvent interact and exchange a proton (H⁺). These solvents can act as both acids and bases, donating or accepting protons.
  • Reaction:
  • The general formula for an amphiprotic solvent is SH. The autoprotolysis reaction can be represented as:
  • 2 SH (solvent) ⇌ SH₂⁺ (lyonium ion) + S⁻ (liate ion)
  • Equilibrium Constant:
  • The equilibrium constant (Kₛ) for autoprotolysis is defined as:
  • Kₛ = [SH₂⁺][S⁻] / [SH]²
  • However, due to the low concentration of ions compared to the neutral solvent molecules, the concentration of [SH] is often considered constant. This simplification leads to the ionic product of water (Kᵅw):
  • Kᵅw = [H⁺][OH⁻]
  • pKᵅw:
  • Due to the small values of Kᵅw (typically on the order of 10^-14 for water at 25°C), it is often expressed using the negative decimal logarithm:
  • pKᵅw = -log₁₀(Kᵅw)
  • Therefore, pKᵅw represents the tendency of an amphiprotic solvent to undergo autoprotolysis and is a measure of the solvent's self-ionization strength.

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