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Ch.17 - Aqueous Ionic Equilibrium
All textbooksTro 4th EditionCh.17 - Aqueous Ionic EquilibriumProblem 123
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Chapter 17, Problem 123

From the data given—where a 0.552-g sample of ascorbic acid (vitamin C) is 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, and the pH of the solution at 10.0 mL of added base was 3.72—determine the molar mass and dissociation constant (Ka) for vitamin C.

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1
Calculate the moles of KOH at the equivalence point using the volume and molarity of KOH: \( \text{moles of KOH} = M \times V \).
Since the moles of KOH equal the moles of ascorbic acid at the equivalence point, use this to find the moles of ascorbic acid.
Determine the molar mass of ascorbic acid by dividing the mass of the sample by the moles of ascorbic acid: \( \text{Molar mass} = \frac{\text{mass}}{\text{moles}} \).
Use the Henderson-Hasselbalch equation to find the pKa at the point where 10.0 mL of KOH is added: \( \text{pH} = \text{pKa} + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right) \).
Calculate the dissociation constant \( K_a \) from the pKa using the relation \( K_a = 10^{-\text{pKa}} \).
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Related Practice
Textbook Question

In analytical chemistry, bases used for titrations must often be standardized; that is, their concentration must be precisely determined. Standardization of sodium hydroxide solutions can be accomplished by titrating potassium hydrogen phthalate (KHC8H4O4), also known as KHP, with the NaOH solution to be standardized. b. The titration of 0.5527 g of KHP required 25.87 mL of an NaOH solution to reach the equivalence point. What is the concentration of the NaOH solution?

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Open Question
A 0.25-mol sample of a weak acid with an unknown pKa was combined with 10.0 mL of 3.00 M KOH, and the resulting solution was diluted to 1.500 L. The measured pH of the solution was 3.85. What is the pKa of the weak acid?
Textbook Question

A 5.55-g sample of a weak acid with Ka = 1.3⨉10-4 was combined with 5.00 mL of 6.00 M NaOH, and the resulting solution was diluted to 750.0 mL. The measured pH of the solution was 4.25. What is the molar mass of the weak acid?

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Open Question
Calculate the pH at the beginning of the titration, at the equivalence point, at one-half of the equivalence point, and at 5.0 mL beyond the equivalence point to sketch the titration curve from Problem 123. Then, choose a suitable indicator for this titration from Table 17.1.
Open Question
If a hard water solution is saturated with calcium carbonate, what volume of the solution has to evaporate to deposit 1.00 × 10^2 mg of CaCO3, given that one of the main components of hard water is CaCO3, and when hard water evaporates, some of the CaCO3 is left behind as a white mineral deposit?
Open Question
If the sodium concentration in blood plasma is 0.140 M, and Ksp for sodium urate is 5.76 * 10^-8, what minimum concentration of urate would result in precipitation?