acid-base titrations. simulation: //users.skynet.be/eddy/titratie.swf strong acid/ strong base
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Acid-base titrations
Simulation: http://users.skynet.be/eddy/titratie.swfStrong acid/ strong base
pH curvespH 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
Equivalence point: the point at which sufficient base has been added to just neutralise the acid (or vice-versa).
strong acidstrong acid (HC (HCll) ) v. strong base v. strong base (NaOH)(NaOH)
pH 1 at the start due to 0.1M HCl
(strong monoprotic acid)
strong acidstrong acid (HC (HCll) ) v. strong base v. strong base (NaOH)(NaOH)
Very little pH change during the initial 20cm3
pH 1 at the start due to 0.1M HCl
(strong monoprotic acid)
strong acidstrong acid (HC (HCll) ) v. strong base v. strong base (NaOH)(NaOH)
Very little pH change during the initial 20cm3
Very sharp change in pH over the addition of less than half a drop of NaOH
pH 1 at the start due to 0.1M HCl
(strong monoprotic acid)
strong acidstrong acid (HC (HCll) ) v. strong base v. strong base (NaOH)(NaOH)
Very little pH change during the initial 20cm3
Very sharp change in pH over the addition of less than half a drop of NaOH
Curve levels off at pH 13 due to excess 0.1M NaOH
(a strong alkali)
strong acidstrong acid (HC (HCll) ) v. strong base v. strong base (NaOH)(NaOH)
pH 1 at the start due to 0.1M HCl
(strong monoprotic acid)
Very little pH change during the initial 20cm3
Sharp change in pH over the addition of less than
half a drop of NH3
Curve levels off at pH 10 due to excess 0.1M NH3
(a weak alkali)
pH 1 at the start due to 0.1M HCl
strong acidstrong acid (HC (HCll) ) v. weak basev. weak base (NH (NH33))
Steady pH change
Sharp change in pH over the addition of less than
half a drop of NaOH
Curve levels off at pH 13 due to excess 0.1M NaOH
(a strong alkali)
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)
weak acid weak acid (CH(CH33COOH) COOH) v. strong basev. strong base (NaOH) (NaOH)
weak acidweak acid (CH (CH33COOH) COOH) v. weak basev. weak base (NH (NH33))
Types
Steady pH change
pH 4 due to 0.1M CH3COOH (weak monoprotic acid)
NO SHARPCHANGE IN pH
Curve levels off at pH 10 due to excess 0.1M NH3
(a weak alkali)
4.3 exercise 4
Other pH curves - Other pH curves - acid v. carbonate
Sodium carbonate reacts with hydrochloric acid in two steps...
Step 1 Na2CO3 + HCl ——> NaHCO3 + NaCl
Step 2 NaHCO3 + HCl ——> NaCl + H2O + CO2
Overall Na2CO3 + 2HCl ——> 2NaCl + H2O + CO2
Other pH curves - Other pH curves - acid v. carbonate
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
Sodium carbonate reacts with hydrochloric acid in two steps...
Step 1 Na2CO3 + HCl ——> NaHCO3 + NaCl
Step 2 NaHCO3 + HCl ——> NaCl + H2O + CO2
Overall Na2CO3 + 2HCl ——> 2NaCl + H2O + CO2
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
There are three sharp pH changes
Each successive addition of NaOH is the same as equal
number of moles are involved.
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
pH of H3PO4 = 1.5
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
pH of NaH2PO4 = 4.4
pH of H3PO4 = 1.5
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
pH of Na2HPO4 = 9.6
pH of NaH2PO4 = 4.4
pH of H3PO4 = 1.5
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Other pH curves - Other pH curves - polyprotic acids (Hpolyprotic acids (H33POPO44))
pH of Na3PO4 = 12
pH of Na2HPO4 = 9.6
pH of NaH2PO4 = 4.4
pH of H3PO4 = 1.5
Phosphoric acid is triprotic; it reacts with sodium hydroxide in three steps...
Step 1 H3PO4 + NaOH ——> NaH2PO4 + H2O
Step 2 NaH2PO4 + NaOH ——> Na2HPO4 + H2O
Step 3 Na2HPO4 + NaOH ——> Na3PO4 + H2O
Page 50, Question 4a), 4bi, 4bii