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19 Nov 2019

A 0.520 g sample of a diprotic acid with a molar mass of 255.8 g/mol is dissolved in water to a total volume of 23.0 mL . The solution is then titrated with a saturated calcium hydroxide solution.

a. Assuming that the pKa values for each ionization step are sufficiently different to see two equivalence points, determine the volume of added base for the first and second equivalence points.

b. The pH after adding 23.0 mL of the base was 3.82. Find the value of pKa1.

c. The pH after adding 20.0 mL past the first equivalence point was 8.17. Find the value of pKa2.

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Lelia LubowitzLv2

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A 0.528 g sample of a diprotic acid with a molar mass of 255.8 g/mol is dissolved in water to a total volume of 26.0 mL . The solution is then titrated with a saturated calcium hydroxide solution. Help on part B and part C?

Part A:Assuming that the pKa values for each ionization step are sufficiently different to see two quivalence points, determine the volume of added base for the first and second equivalence points. ( answer: 1st eq:97.9mL;2nd eq:196mL)

Part B: The pH after adding 26.0 mL of the base was 3.82. Find the value of pKa1

Part C:The pH after adding 19.0 mL past the first equivalence point was 8.21. Find the value of pKa2

123. A 0.552-g sample of ascorbic acid (vitamin C) was dissolved in water to a total volume of 20.0 mL and titrated with 0.1103 M KOH. The equivalence point occurred at 28.42 mL. The pH of the solution at 10.0 mL of added base was 3.72. From this data, determine the molar mass and K, for vitamin C.

When creating a titration curve for a weak base, the pH of the initial solution requires setting up a table showing the initial, change, and equilibrium values for each species and plugging these into the equilibrium constant expression. The expression for the bicarbonate ion is Ka1=[H2CO3][H+][HCO3â] For an anion that can both hydrolyze and produce H+, the pH of a concentrated solution can be more easily approximated using the equation pH=12(pKa1+pKa2) During the titration before the equivalence point, provided that the concentration of acid is significantly more than the concentration of base, the Henderson-Hasselbalch equation can be used to approximate the pH: pH=pKa+log[base][acid] At the equivalence point, the solution is no longer a buffer, but contains the weak acid H2CO3. The change in concentration of the bicarbonate ion is significant, and the equilibrium constant expression for Ka1 must again be used to find the concentration of hydronium ions. After the equivalence point, the strong acid will control the pH.

Part A

A 10.0-mL sample of 1.0 M NaHCO3 is titrated with 1.0 M HCl (hydrochloric acid). Approximate the titration curve by plotting the following points: pH after 0 mL HCl added, pH after 1.0 mL HCl added, pH after 9.5 mL HCl added, pH after 10.0 mL HCl added (equivalence point), pH after 10.5 mL HCl added, and pH after 12.0 mL HCl added.

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