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Ch.17 - Additional Aspects of Aqueous Equilibria
All textbooksBrown 14th EditionCh.17 - Additional Aspects of Aqueous EquilibriaProblem 94
Chapter 17, Problem 94

What is the pH of a solution made by mixing 0.30 mol NaOH, 0.25 mol Na2HPO4, and 0.20 mol H3PO4 with water and diluting to 1.00 L?

Verified step by step guidance
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Step 1: Identify the species present in the solution. NaOH is a strong base, Na2HPO4 is a salt that can act as a weak base, and H3PO4 is a weak acid.
Step 2: Determine the reactions that will occur. NaOH will react with H3PO4 to form water and Na2HPO4. Write the balanced chemical equation for this reaction: \[ \text{NaOH} + \text{H}_3\text{PO}_4 \rightarrow \text{Na}_2\text{HPO}_4 + \text{H}_2\text{O} \].
Step 3: Calculate the moles of each reactant and product after the reaction. Use stoichiometry to determine the limiting reactant and the amount of each species remaining or formed.
Step 4: Determine the dominant species in the solution after the reaction. Consider the remaining moles of NaOH, Na2HPO4, and H3PO4 to identify the predominant acid-base pair.
Step 5: Use the Henderson-Hasselbalch equation to calculate the pH of the solution. The equation is \[ \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \], where \([\text{A}^-]\) is the concentration of the conjugate base and \([\text{HA}]\) is the concentration of the weak acid.
Related Practice
Textbook Question

A sample of 0.1687 g of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.1150 M NaOH. The acid required 15.5 mL of base to reach the equivalence point. (b) After 7.25 mL of base had been added in the titration, the pH was found to be 2.85. What is the Ka for the unknown acid?

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Textbook Question
Mathematically prove that the pH at the halfway point of a titration of a weak acid with a strong base (where the volume of added base is half of that needed to reach the equivalence point) is equal to pKa for the acid.
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Open Question
A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62. Estimate the pKa of the weak acid.
Textbook Question

Suppose you want to do a physiological experiment that calls for a pH 6.50 buffer. You find that the organism with which you are working is not sensitive to the weak acid H2A 1Ka1 = 2 * 10-2; Ka2 = 5.0 * 10-72 or its sodium salts. You have available a 1.0 M solution of this acid and a 1.0 M solution of NaOH. How much of the NaOH solution should be added to 1.0 L of the acid to give a buffer at pH 6.50? (Ignore any volume change.)

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Open Question
How many microliters of 1.000 M NaOH solution must be added to 25.00 mL of a 0.1000 M solution of lactic acid CH3CH(OH)COOH or HC3H5O3 to produce a buffer with pH = 3.75?
Textbook Question

Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?

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