Monoprotic Acid and Bases

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Chapter 10

• Monoprotic Acid and Bases

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Strong Acids and Bases

• Compound that when dissolved in water will fully
  dissociate.
• This is a factor of our very universal solvent
  and its special properties. This is called the
  leveling effect of water.
• Our strong acids are
• HCl
• HBr
• HI
• HNO3
• HClO4
• H2SO4 (first ionization)

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Strong Acids

• The acid dissociation equilibrium
• HA H2O H3O A-
• The equilibrium constant values for our strong
  acids
• Acid Ka
• HCl 7900
• HBr 630 000
• HI 25 000 000 000
• HNO3 25

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Strong Acids

• The strongest of the common strong acids is
  perchloric acid. (HClO4)
• This strengths can be shown be going to other
  solvents other than water. Acidic acid is a
  common choice.

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Strong Acid and Bases

• Our strong bases are
• NaOH
• KOH
• LiOH
• Sr(OH)2

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Determining pH

• Since they completely dissociate we get the same
  concentration of H as the dissolved acid or
  base.
• So if a solution is made up to be 1.00x10-2 M HCl
  then the pH will be pH - log H -log
  (1.00x10-2) 2.?????? (How many sig figs?)
• More correctly we should correct for activity so
  we should have pH -logAH -log gH -log
  (0.914)(1.00x10-2) 2.03905 (How many sig figs?)
• But we will not bother to correct unless called
  on to do so.

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Strong Acids

• pH of strong base solutions.
• pH of a 1.0x10-3 M NaOH solution.
• Na .0010 and OH- 0.0010
• Then pOH is 3.00
• Since HOH- Kw
• pH pOH 14.00
• Then pH of this solution is 11.00
• Kw varies with temperature so you need to account
  for that also.

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Strong Acids

• What if we make up a solution that is 1.0x10-5 M
  HNO3. The pH would be 5.00.
• If we were to dilute this solution by 1000 fold.
  That is take 1.00 mL and dilute to 1.00 Liters.
  What is the pH then.

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Strong Acids

• It can not be pH 8. That would mean that we have
  made up a solution that is basic from and acid
  and water???
• How would you calculate this?
• This is a case for Chapter 9. Systematic
  treatment of equilibrium.

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Strong Acids

• What do we know?
• CHNO3 1.00x10-8
• From this we can see that CNO3- 1.00x10-8
• What is the charge balance of this sytem.
• H NO3- OH-
• We also have our Kw expression.
• So H CNO3 Kw/H

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Weak Acids/Bases

• These are acids and bases that do not fully
  dissociate when placed in aqueous solution.
• Examples
• Acetic Acid
• Benzoic Acid
• Hydrofluoric Acid
• Ammonia

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Weak Acids/Bases

• Weak acid equilibrium
• HA H A-

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Weak Acids and Bases

• Weak Base equlibrium (Also called hydrolysis
  constant)
• B H2O BH OH-

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Conjugate Pairs
Formic Acid Formate Ion An acid / conjugate
base pair
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Conjugates
Ammonia Ammonium
Ion Base Conjugate Acid
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Table G

• The Table in the back of the book. Starting on
  page AP12 lists all acids and bases as acids. It
  will give the proper base name but show the
  structure for the conjugate acid form. When
  there is more than one acidic group then the
  book will indicate which proton goes with the
  given pKa.

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Table G
8- Hydroxyquinoline 4.91 (NH) 9.81 (OH)
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Buffers

• When you add a weak acid and its conjugate then
  you will get a buffer. Buffers resist the rapid
  change in pH when acid or base is added to the
  solution.
• pH pKa log (base/acid)
• pH control is important since many processes are
  pH dependent.

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Buffers

• Made two different ways
• Mix an acid and its conjugate base
• Acetic acid and sodium acetate
• Ammonium Chloride and aqueous ammonium
• Prepare a solution of an acid or base and
  generate the conjugate by addition of strong acid
  or base.
• Acetic acid and add NaOH

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Buffers

• When adding both forms the concentration of the
  buffer will be the sum of the concentration of
  both forms
• When generating from strong conjugate then add
  the moles of acid needed at the final volume.

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Preparation

• Weight out the number of moles of buffer needed
  and dilute to 80 final volume.
• Place pH electrode into solution
• Add strong acid/base until pH is reached.
• Dilute to mark

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Buffer Capacity

• The amount of acid or base that can be added
  before the buffer is consumed.
• b dCb / dpH - dCa / dpH

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Buffer pH

• Ionic Strength
• Temperature

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What about extreme conditions

• FHA FA- HA A-
• Na H OH- A-
• HA FHA H OH-
• A- FA- H OH-
• pH pKa log corr A- / corr HA

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