Plotting a Titration Curve for a Carbonate- Bicarbonate System Carbonic acid (H2
ID: 866770 • Letter: P
Question
Plotting a Titration Curve for a Carbonate- Bicarbonate System Carbonic acid (H2CO3) is a weak diprotic acid with Kal = 4.43 times 10-7 and Ka2 = 4.73 x 10-11. The bicarbonate ion, HCO3-, reacts with the acid as shown in the equation hco3- + h+ h2co3 Salts of the bicarbonate ion, such as sodium bicarbonate ( NaHCO3) act as weak bases. Creating titration curves When creating a titration curve for a weak base, the pH of the initial solution requires setting up species and plugging these into the equilibrium constant expression. The expression for the bica For an anion that can both hydrolyze and produce H+, the pH of a concentrated solution can be During the titration before the equivalence point, provided that the concentration of acid is significant Hasselbalch equation can be used to approximate the pH: At the equivalence point, the solution is no longer a buffer, but contains the weak acid Ha2CO3. the equilibrium constant expression for Ka1 must again be used to find the concentration of hydrogen After the equivalence point, the strong acid will control the pH. Part A A 10.0-mL sample of 1.0 M NaHCO: is titrated with 1.0 M HC1 (hydrochloric acid). pH after 0 mL HC1 added, pH after 1.0 mL HC1 added, pH after 9.5 mL HC1 added, pH after 10.0 mL HC1 added (equivalence point), pH after 10.5 mL HC1 added, and pH after 12.0 mL HC1 added.Explanation / Answer
pKa1 = -log Ka1 = 7- log4.43 = 6.35
pKa2 = - log Ka2 = 11