Hydrophobic vs Hydrophillic pH and Buffers

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Hydrophobic vs HydrophillicpH and Buffers

• Lecture 6

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Hydrophobicity

• In chemistry, hydrophobicity (from the combining
  form of water in Attic Greek hydro- and for fear
  phobos) refers to the physical property of a
  molecule that is repelled from water.
• Hydrophobic molecules tend to be non-polar and
  thus prefer other neutral molecules and nonpolar
  solvents.
• Examples of hydrophobic molecules include the
  oils, fats, and greasy substances in general.

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Hydrophophilicity

• A hydrophilic molecule or portion of a molecule
  is charge-polarized and capable dissolving more
  readily in water than in oil. Hydrophilic
  molecules are also known as polar molecules.

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Acid

• Any substance that when dissolved in water will
  donate a hydrogen ion to the solution or increase
  the hydrogen ion concentration of the solution
• Typically the chemical formula will have a
  Hydrogen in it (HCl, CH3COOH).
• HA ? H A-

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Base

• Any substance that when dissolved in water will
  decrease the hydrogen ion concentration
• Typically bases will have an OH in the chemical
  formula (NaOH)
• B- H ? BH

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Strong or Weak?
The strength of the acid or base is dependent on
the ability of a compound to separate into ions
in solution
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pH

• pH the scale used to measure of how acidic or
  basic a solution is.
• The name, pH, has been purported to come from a
  variety of places including pondus hydrogenii
  (Latin), potentiel hydrogène
  (French), and potential of hydrogen (English).

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A pH value between 0 and 14 is used to indicate
the concentration of H or OH- in solution.
Mathematically, the pH of a solution is defined
as the negative common logarithm of the H
concentration pH -log H or H
10-pH Acidic solution pH lt 7 H gt 1.00 x
10-7 M Neutral solution pH 7 H 1.00 x
10-7 M Basic solution pH gt 7 H lt 1.00 x 10-7
M
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Buffers

• Buffer solutions are solutions which resist
  change in pH upon addition of small amounts of
  acid or base, or upon dilution.
• The most commonly used buffers are weak acids or
  bases such as CH3COOH or Na3PO4.

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Titration Curve
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pH Indicators
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pH meter
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Using a pH meter

• Remove probe from storage buffer
• Place probe over rinse beaker, rinse with water,
  and dry probe with a kim wipe
• Place probe in solution that is to be tested
• Maintain constant stirring to evenly distribute
  the H ions in solution
• When measurement is complete, repeat step 2 with
  the probe and return to storage buffer

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Activity

• Create a titration curve for a buffer of your
  choice using the pH meter