Acid Base Titrations

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Chapter 16.7 and 16.8

• Acid Base Titrations
• Buffered Solutions

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16.7 Acid Base Titrations

• Strong acids contain H
• Strong bases contain OH-
• H OH- ? H2O
• Neutralization reaction equal amounts of H and
  OH- results in a neutral solution (pH7).
• Titration involves the delivery of a measured
  volume of a solution of known concentration
  (titrant) into the solution being analyzed
  (analyte)

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Titrations

• Standard solution solution of known
  concentration
• Buret cylindrical device allows for a measured
  amount of liquid to be dispensed.
• Stochiometry point or equivalence point Keep
  adding titrant until all of analyte reacts with
  titrant, when pH 7

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(No Transcript)
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Titration Curve or pH curve

• A titration curve is a plot of the pH of a
  solution (acid or base) against the volume of
  titrant added (base or acid).

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Figure 17.11
Curve for the titration of a strong acid by
a strong base.
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Titration problems

• What volume of .1 M NaOH is needed to titrate
  (neutralize) 50.0 mL of .2 M HNO3?
• We need moles of OH- added to equal moles of H
  present.
• M m / L
• Ma x Va ma and Mb x Vb mb
• So, Ma x Va (mb/ma) Mb x Vb
• mb/ma (mole to mole ratio)

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• What volume of .1 M NaOH is needed to titrate
  (neutralize) 50.0 mL of .2 M HNO3?
• NaOH HNO3 ? NaNO3 HOH
• MaVa (b/a) MbVb
• (.2 M)(50. mL)(1/1) (.1 M)(V)
• V100 mL of NaOH

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Problem

• It takes 25mL of H2SO4 to titrtate 30mL of 3 M
  NaOH. Calculate the molarity of H2SO4.
• H2SO4 2 NaOH ? Na2SO4 2 HOH
• MaVa (b/a) MbVb
• Ma (.026L) (2/1) (3)(.030L)
• Ma 1.7

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Problem

• When 14.3 mL of 0.573 M Ca(OH)2 are neutralized
  with 0.426 M HNO2 what volume of acid would be
  used?
• Ca(OH)2 2 HNO2 ? Ca(NO3)2 2HOH
• MaVa (b/a) MbVb
• (.426)(V) (1/2) (.573)(14.3 mL)
• V acid 66.67 mL

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Buffers
Blood is a buffer. Bloods pH ranges between
7.35 7.45. If the pH of blood drops below 6.8
or is higher than 7.8, you can not survive. CO2
H2O ?? H2CO3 ?? H HCO3-
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16.8 Buffers

• A buffer is a solution characterized by the
  ability to resist large changes in pH when
  limited amounts of acid or base are added to it.

• Buffers contain either a weak acid and its
  conjugate base or a weak base and its conjugate
  acid.

• Thus, a buffer contains both an acid species and
  a base species in equilibrium.

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Buffers

• Buffering capacity the amount of H or OH-
  that a buffer system can absorb with out
  significant changes in pH.
• Aspirin is an acid. When someone overdoses, the
  body can not neutralize the aspirin.

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Buffers
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Buffers

• If you add an acid
• H HCO3- ? H2CO3
• (pop) (blood)
• If you add a base
• OH- H2CO3 ? H2O HCO3-

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Buffers

• Blood buffers H2CO3 /HCO3- and
  H2PO4-/HPO4-2
• Kidneys Excrete acidic/basic solutions and back
  up the neutralization system
• Breathing rate controls amount of CO2 in body.
  CO2 H2O ? H2CO3 (carbonic acid)
• Acidosis or alkalosis can cause death.