Textbook Question
What is the pH of a buffer solution prepared by dissolving 0.250 mol of NaH2PO4 and 0.075 mol of NaOH in enough water to make 1.00 L of solution? (Ka (H2PO4-) = 6.2 X 10^-8)
(a) 6.32
(b) 6.83
(c) 7.21
(d) 7.71
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Ch.17 - Applications of Aqueous Equilibria
Chapter 17, Problem 9
A 25.00 mL sample of 1.00 M CH3CO2H is titrated with 1.00 M NaOH. Calculate the pH after 30.00 mL of NaOH has been added. (Ka = 1.8 x 10^-5) (a) 6.90 (b) 9.36 (c) 11.54 (d) 12.95
Verified step by step guidance1
Calculate the initial moles of CH3CO2H using the formula: moles = concentration \( \times \) volume. Here, the concentration is 1.00 M and the volume is 25.00 mL.
Calculate the moles of NaOH added using the same formula: moles = concentration \( \times \) volume. The concentration is 1.00 M and the volume is 30.00 mL.
Determine the limiting reactant by comparing the initial moles of CH3CO2H and the moles of NaOH added. Since NaOH is in excess, calculate the moles of NaOH remaining after the reaction.
Use the Henderson-Hasselbalch equation to find the pH of the solution. The equation is: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \( \text{pKa} = -\log(\text{Ka}) \).
Substitute the concentrations of the acetate ion \([\text{A}^-]\) and acetic acid \([\text{HA}]\) into the Henderson-Hasselbalch equation to calculate the pH.
Related Practice
Open Question
Which is the best acid-base pair to use in the preparation of a buffer with pH = 10.5? (a) HOI and OI- (Ka = 2.0 x 10^-11) (b) HNO2 and NO2- (Ka = 4.5 x 10^-4) (c) HIO3 and IO3- (Ka = 1.7 x 10^-1) (d) H2PO4^- and HPO4^2- (Ka = 6.2 x 10^-8)
Open Question
Calculate the concentrations of NH4+ and NH3 and the pH in a solution prepared by mixing 20.0 g of NaOH and 0.500 L of 1.5 M NH4Cl. Assume that the volume remains constant.
Textbook Question
The pH titration curve applies to the titration of 40.0 mL of a 0.100 M solution of an acid with 0.100 M NaOH. What are the approximate pKa values for this acid?
(a) pKa1 = 5, pKa2 = 10
(b) pKa1 = 7, pKa2 = 11
(c) pKa1 = 5, pKa2 = 10, pKa3 = 13
(d) pKa1 = 5, pKa2 = 7, pKa3 = 10
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Textbook Question
What is the solubility-constant expression for Ca3(PO4)2 (s)?
(a) [Ca2+]3 [PO43-]2
(b) [Ca2+]3 [PO43-]2 / [Ca3(PO4)2]
(c) [Ca(PO4)2] / [Ca2+]3 [PO43-]2
(d) [Ca2+]2 [PO43-]3
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Open Question
What is the molar solubility of Ag2SO3 in water? The solubility-product constant for silver sulfite is 1.5 x 10^-14 at 25 °C. (a) 1.2 x 10^-7 M (b) 2.0 x 10^-5 M (c) 8.7 x 10^-8 M (d) 1.6 x 10^-5 M