Potential Hydrogen Ion Concentration

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Potential Hydrogen Ion Concentration

• (pH Scale)

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The pH of some aqueous solutions
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Acids, Bases and pH

• 1. Only a hydrogen ion (proton with 1
• charge) is actually transferred.
• 2. Transferred proton binds to an unshared
  orbital of the second water molecule creating a
  hydronium ion (H3O).
• 3. Water molecule that lost a proton has a net
  negative charge and is called a hydroxide ion
  (OH-).
• H2O H2O ? H3O OH-

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Chemical reaction hydrogen bond shift
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Acids, Bases and pH

• 4. By convention, ionization of H2O is
• expressed as the dissociation
• into H and OH-
• H2O ? H OH-
• 5. Reaction is reversible.
• 6. At equilibrium, most of the H2O is
• not ionized.

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Acids, Bases and pH

• A solution in which
• H OH- is a neutral solution.
• H gt OH- is an acidic solution.
• H lt OH- is a basic solution.

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Acids, Bases and pH

• pH Negative log10 of the H expressed
• in moles per liter.
• pH of 7 is a neutral solution.
• pH lt 7 is an acidic solution.
• PH gt 7 is a basic solution.
• Most biological fluids are within the
• pH range of 6 to 8. There are some exceptions
• such as stomach acid with pH of 1.

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Acids, Bases and pH

• Each pH unit represents a tenfold difference
• (scale is logarithmic ), so a slight change in
• pH represents a large change in
• actual H.
• pH -log H or H 10 pH M
• pOH -log OH- or OH- 10 pOH M
• pH pOH 14

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Acids, Bases and pH

• For Example
• If the concentration of OH- in an aqueous
  solution is 10-3, what is the pH?

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Acids, Bases and pH

• pOH -log OH- pH pOH 14
• pOH -log 10-3 pH 3 14
• pOH 3 pH 14 3
• Final Answer pH 11

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Acids, Bases and pH

• For Example
• What is the H concentration in a solution that
  has a pH of 7?

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Acids, Bases and pH

• Answer
• 1 X 10 7 M

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Acids, Bases and pH

• For example
• How much greater is the H in a solution
• with pH 2 than in a solution with pH 6?

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Acids, Bases and pH

• Answer
• pH 2 H of 10-2 1 M
• 100
• pH 6 H of 10-6 1 M
• 1,000,000
  
  
• 10,000 times greater.

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Acids, Bases and pH

• Buffers
• By minimizing wide fluctuations in pH,
• buffers help organisms maintain the pH of
• body fluids within the narrow range
• necessary for life (usually pH 6-8).

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Acids, Bases and pH

• Buffer
• 1. Substances that prevent large
• sudden changes in pH.
• 2. Consist of combinations of H -donor and
• H -acceptor forms of weak acids or
• bases.
• 3. Work by accepting H ions from solution
• when they are in excess, and by donating
• H ions to the solution when they have
  been
• depleted.

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Acids, Bases and pH

• For example
• Bicarbonate buffer
• H2CO3 HCO3- H
• H donor H
  acceptor
• Weak acid Weak
  base