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Why do Titration Curves Look Like THAT ????
04/21/23 1
• Calculate the pH when the following quantities of 0.100 M NaOH solution have been added to 50.0 mL of 0.100 M HCl solution:A. 30.0 mLB, 49.0 mLC. 49.5 mLD. 50.0 mLE. 50.5 mLF. 60.0 mL
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Solution for 30.0 mL NaOHBoth Na+ and Cl- are spectator ions. Find how many moles H+ and moles OH- present,
then calculate how many mole of each ion remain after neutralization.
Before Change Remaining
H+ 0.005 -0.003 0.002OH- 0.003 -0.003 0
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.003soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL0.30
• Remaining H+ mole / new soln volume
New pH now…
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H M 0.029L 1
mL 1000
mL) 30.0(50.0
H mol 0.002
6.1)029.0log( pH
Solution for 49.0 mL NaOH
Before Change Remaining
H+ 0.005 -0.0049 0.0001OH- 0.0049 -0.0049 0
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.0049soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL0.49
• Remaining H+ mole / new soln volume
New pH now…
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H M 0.0010L 1
mL 1000
mL) 49.0(50.0
H mol 0.0001
0.3)0010.0log( pH
Solution for 49.5 mL NaOH
Before Change Remaining
H+ 0.005 -0.00495 0.00005OH- 0.0049 -0.00495 0
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.00495soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL5.49
• Remaining H+ mole / new soln volume
New pH now…
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H M 105.0L 1
mL 1000
mL) 49.5(50.0
H mol 0.00005 4-
3.3)100.5log( 4 pH
Solution for 50.0 mL NaOH
Before Change Remaining
H+ 0.005 -0.005 0OH- 0.005 -0.005 0
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.0050soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL0.50
• [H+] = [OH-] = 0 M• Neutral • pH = 7
New pH now…
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Solution for 50.5 mL NaOH
Before Change Remaining
H+ 0.005 -0.005 0OH- 0.00505 -0.005 0.00005
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.00505soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL5.50
• Remaining OH- mole / new soln volume
New pH now…
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-4--
OH M 104.98L 1
mL 1000
mL) 50.5(50.0
OH mol 0.00005
7.103.314
3.3
)1098.4log( 4
pH
pOH
pOH
Solution for 60.0 mL NaOH
Before Change Remaining
H+ 0.005 -0.005 0OH- 0.006 -0.005 0.001
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H mol 0.005soln L 1
H mol 0.100
mL 1000
L 1H mL0.50
--
OH mol 0.0060soln L 1
OH mol 0.100
mL 1000
L 1NaOH mL0.60
• Remaining OH- mole / new soln volume
New pH now…
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-3--
OH M 109.09L 1
mL 1000
mL) 60.0(50.0
OH mol 0.001
0.120.214
0.2
)1009.9log( 3
pH
pOH
pOH
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Titration curve for a strong acid by a strong base
Any indicator that changes color along the steep portion of the titration curve is suitable for the titration. Methyl violet changes color too soon, and alizarin yellow R too late.
Subtle vocabulary pointEquivalence point:
where equal moles of acid and base are present.
End Point: where an indicator chemical changes color. It may not be exactly at the equivalence point, but generally very close.
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