Acid-base titrations

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Acid-base titrations
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Simulation http//users.skynet.be/eddy/titratie.s
wf Strong acid/ strong base
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pH curves
Types There are four types of acid-base
titration each has a characteristic
curve. strong acid (HCl) v. strong base
(NaOH) weak acid (CH3COOH) v. strong
alkali (NaOH) strong acid (HCl) v. weak
base (NH3) weak acid (CH3COOH) v. weak
base (NH3) In the following examples, alkali
(0.1M) is added to 25cm3 of acid (0.1M) End
points need not be neutral due to the
phenomenon of salt hydrolysis
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Equivalence point the point at which sufficient
base has been added to just neutralise the acid
(or vice-versa).
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strong acid (HCl) v. strong base (NaOH)
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strong acid (HCl) v. strong base (NaOH)
pH 1 at the start due to 0.1M HCl (strong
monoprotic acid)
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strong acid (HCl) v. strong base (NaOH)
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong
monoprotic acid)
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strong acid (HCl) v. strong base (NaOH)
Very sharp change in pH over the addition of less
than half a drop of NaOH
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong
monoprotic acid)
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strong acid (HCl) v. strong base (NaOH)
Curve levels off at pH 13 due to excess 0.1M
NaOH (a strong alkali)
Very sharp change in pH over the addition of less
than half a drop of NaOH
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl (strong
monoprotic acid)
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strong acid (HCl) v. weak base (NH3)
Curve levels off at pH 10 due to excess 0.1M
NH3 (a weak alkali)
Sharp change in pH over the addition of less than
half a drop of NH3
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl
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weak acid (CH3COOH) v. strong base (NaOH)
Curve levels off at pH 13 due to excess 0.1M
NaOH (a strong alkali)
Sharp change in pH over the addition of less than
half a drop of NaOH
Steady pH change
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)
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weak acid (CH3COOH) v. weak base (NH3)
Curve levels off at pH 10 due to excess 0.1M
NH3 (a weak alkali)
NO SHARP CHANGE IN pH
Steady pH change
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)
Types
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4.3 exercise 4
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Other pH curves - acid v. carbonate
Sodium carbonate reacts with hydrochloric acid
in two steps... Step 1 Na2CO3 HCl gt
NaHCO3 NaCl Step 2 NaHCO3 HCl gt
NaCl H2O CO2 Overall Na2CO3
2HCl gt 2NaCl H2O CO2
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Other pH curves - acid v. carbonate
Sodium carbonate reacts with hydrochloric acid
in two steps... Step 1 Na2CO3 HCl gt
NaHCO3 NaCl Step 2 NaHCO3 HCl gt
NaCl H2O CO2 Overall Na2CO3
2HCl gt 2NaCl H2O CO2
There are two sharp pH changes
The second addition of HCl is exactly the same as
the first because the number of moles of HCl
which react with the NaHCO3 is the same as that
reacting with the Na2CO3.
17.50cm3
35.00cm3
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
There are three sharp pH changes
Each successive addition of NaOH is the same as
equal number of moles are involved.
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
pH of H3PO4 1.5
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
pH of NaH2PO4 4.4
pH of H3PO4 1.5
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
pH of Na2HPO4 9.6
pH of NaH2PO4 4.4
pH of H3PO4 1.5
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Other pH curves - polyprotic acids (H3PO4)
Phosphoric acid is triprotic it
reacts with sodium hydroxide in three
steps... Step 1 H3PO4 NaOH gt
NaH2PO4 H2O Step 2 NaH2PO4 NaOH
gt Na2HPO4 H2O Step 3 Na2HPO4
NaOH gt Na3PO4 H2O
pH of Na3PO4 12
pH of Na2HPO4 9.6
pH of NaH2PO4 4.4
pH of H3PO4 1.5
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Page 50, Question 4a), 4bi, 4bii