A.) A 20.0 mL sample of 0.0600 M carbonic acid (H2CO3) is titrated with 5.00 mL of 0.0960 M KOH. What is the solution pH to the nearest hundredths place? pKa1 = 6.35 and pKa2 = 10.33.
B.) A 20.0 mL sample of 0.0600 M carbonic acid (H2CO3) is titrated with 0.0960 M KOH. How many mL of titrant are required to reach the first equivalence point?
C. )A 20.0 mL sample of 0.0600 M carbonic acid (H2CO3) is titrated with 0.0960 M KOH. To the nearest hundredth, what is the pH at the first equivalence point?
D.) A 20.0 mL sample of 0.0600 M carbonic acid (H2CO3) is titrated with 15.0 mL of 0.0960 M KOH. To the nearest hundredths, what is the pH of the solution? pKa1 = 6.35 and pKa2 = 10.33
pKa1 = 6.35 and pKa2 = 10.33.
A.)
millimoles of H2CO3 = 20.0 x 0.060 = 1.2
millimoles of KOH = 5.00 x 0.0960 = 0.48
H2CO3 + KOH -----------> HCO3- + H2O
1.2 0.48 0 0
0.72 0 0.48
pH = pKa1 + log [HCO3- / H2CO3]
= 6.35 + log [0.48 / 0.72]
pH = 6.17
B.)
At first equivalence point :
mmoles of H2CO3 = mmoles of KOH
20.0 x 0.0600 = 0.0960 x V
V = 12.5 mL
volume of titrant = 12.5 mL
C)
At first equivalence point :
pH = pKa1 + pKa2 / 2
= 6.35 + 10.33 / 2
pH = 8.34
D)
mmoles of KOH = 15.0 x 0.0960 = 1.44
H2CO3 + KOH -----------> HCO3- + H2O
1.2 1.44 0 0
0 0.24 1.2
HCO3- + KOH -----------> CO32- + H2O
1.2 0.24 0 0
0.96 0 0.24
pH = 10.33 + log [0.24/ 0.96]
pH = 9.73
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