Question 6 1.25 pts A 0.500 L buffer solution is O.973 M in acetic acid and 0.97

Question

Question 6 1.25 pts A 0.500 L buffer solution is O.973 M in acetic acid and 0.973 M in sodium acetate. Acetic acid has a pKa of 4.74, making the pH of this solution 4.74. What is the pH after addition of 0.030 mol of NaOH? Question 7 1 pts A 0.500 L container is filled with pure water. What is the pH in the initial container? What is the pH in the container after the addition of 0.030 mol of NaOH? Comparing your result with the previous question, did water or the buffer have a larger change in pH due to the addition of 0.030 mol of NaOH? Enter your pH values to 3 significant figures. Answer the last question by typing in either "buffer" or "water"

Explanation / Answer

6)

mol of NaOH added = 0.03 mol

CH3COOH will react with OH- to form CH3COO-

Before Reaction:
mol of CH3COO- = 0.973 M *0.5 L
mol of CH3COO- = 0.4865 mol

mol of CH3COOH = 0.973 M *0.5 L
mol of CH3COOH = 0.4865 mol

after reaction,
mol of CH3COO- = mol present initially + mol added
mol of CH3COO- = (0.4865 + 0.03) mol
mol of CH3COO- = 0.5165 mol

mol of CH3COOH = mol present initially - mol added
mol of CH3COOH = (0.4865 - 0.03) mol
mol of CH3COOH = 0.4565 mol

since volume is both in numerator and denominator, we can use mol instead of concentration
use:
pH = pKa + log {[conjugate base]/[acid]}
= 4.74+ log {0.5165/0.4565}
= 4.79

Answer: 4.79

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