Acid and Base

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Acid and Base

• Titration calculations
• 7-5

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Titration calculations

• Chemists use the fact that the pH breaks sharply
  when an acid is neutralized by a base to
  accurately determine the concentration of either
  the acid or base solution.
• At this point there is stoichiometrically equal
  amounts of acid and base.

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• Molarity moles
• Liter
• Moles of a substance
• Concentration (M) x Volume (L)

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• Balance Base (Bb) x Moles of Acid
• Moles of Base x Balance Acid (Ba)
• Bb x Ca x Va Ba x Cb x Vb

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equivalence point

• This point can be determined within a few drops
  of base solution added, because the pH changes
  sharply near this point.
• is when there is an equal amount of moles of
  acid and base

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• Chemists use an indicator to signal the pH
  change. An indicator is a substance that changes
  color with certain changes in pH. The
  experimenter picks a indicator that changes color
  in the pH range that corresponds to the break in
  the titration curve.
• This will vary depending on what combinations of
  acids and bases are titrated. When the indicator
  changes color the titration is said to have
  reached it's endpoint. If the titration is done
  properly the endpoint is very close to the
  equivalence point.

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Steps for the titrations

• Step 1 balance the neutralization equation.
• determine balance of acid and base.
• Step 2 determine the given information.
• Step 3 determine what information is required
• Step 4 solve using the equation below
• Bb x Ca x Va Ba x Cb x Vb

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example

• Calculate the concentration of a nitric acid
  solution (HNO3 ) if a 20. ml sample of the acid
  required an average volume of 55 ml of a 0.047
  mol/l solution of Ba(OH)2 to reach the endpoint
  of the titration.

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Step 1

• 2 HNO3 Ba(OH)2 -----gt Ba(NO3)2 2 H2O
• Balance Base 1Balance Acid 2

base
acid
Look at the coefficients to decide these numbers
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Step 2

• Volume Acid 20 mlVolume Base (average) 55 ml
  Concentration of Base 0.047 mol/l

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Step 3

• Concentration of the acid

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Step 4

• Solve using the equation.
• Bb x Ca x Va Ba x Cb x Vb
• (1)( Ca)(20 ml) (2)(0.047 mol/l)(55 ml)
  
• Ca 0.2585 mol/l
• Ca 0.26 M

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example

• Calculate the concentration of a sulfuric acid
  solution (H2SO4 ) if a 40. ml sample of the acid
  required an average volume of 125 ml of a 0.096 M
  solution of NaOH to reach the endpoint of the
  titration.

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• H2SO4 2 NaOH ? 2 H2O Na2SO4
• Bb x Ca x Va Ba x Cb x Vb
• (2)(Ca)(40 ml) (1)(0.096 mol/l)(125 ml)
  
• Ca 0.15 mol/l

base
acid
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• Solve using the equation.
• Bb x Ca x Va Ba x Cb x Vb
• (1)( Ca)(20 ml) (2)(0.047 mol/l)(55 ml)
  
• Ca 0.2585 mol/l
• Ca 0.26 M