This question concerns part 2 of the lab.Your target pH is still 5.40, and you are starting with 10.0 mL of 0.100 M sodium acetate solution. To create the buffer, you use a burette filled with 0.100 M HCl solution and dip a pH meter into the sodium acetate solution.You add HCl from the burette until the pH meter reads 5.40 exactly.How volume of HCl (in mL) should have been added from the burette at this point ? Please note in real life the actual volume needed may differ from the "ideal" calculated value. Report your answer to two decimal places.Answer:
Question
This question concerns part 2 of the lab.Your target pH is still 5.40, and you are starting with 10.0 mL of 0.100 M sodium acetate solution. To create the buffer, you use a burette filled with 0.100 M HCl solution and dip a pH meter into the sodium acetate solution.You add HCl from the burette until the pH meter reads 5.40 exactly.How volume of HCl (in mL) should have been added from the burette at this point ? Please note in real life the actual volume needed may differ from the "ideal" calculated value. Report your answer to two decimal places.Answer:
Solution
To answer this question, we need to use the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]).
In this case, we know that the pKa of acetic acid (which is the acid form of the sodium acetate) is 4.76. We also know that the target pH is 5.40.
So, we can rearrange the equation to solve for the ratio of [A-]/[HA]:
5.40 = 4.76 + log([A-]/[HA])
This simplifies to:
log([A-]/[HA]) = 5.40 - 4.76 = 0.64
Taking the antilog of both sides gives us:
[A-]/[HA] = 10^0.64 = 4.47
This ratio tells us that for every 1 mole of HA (acetic acid), we need 4.47 moles of A- (acetate ion).
Since we started with 10.0 mL of 0.100 M sodium acetate solution, we initially have 1.00 mmol of acetate ion.
To achieve the desired ratio, we need to add enough HCl to convert some of the acetate ion to acetic acid.
Since HCl reacts with sodium acetate in a 1:1 ratio, the amount of HCl needed is simply the difference between the initial amount of acetate and the desired amount of acetic acid.
So, we need to add enough HCl to convert 1.00 mmol - 1.00 mmol / 4.47 = 0.78 mmol of acetate to acetic acid.
Since the concentration of the HCl solution is 0.100 M, the volume of HCl needed is (0.78 mmol) / (0.100 M) = 7.78 mL.
So, ideally, you should have added 7.78 mL of HCl from the burette to achieve a pH of 5.40.
Please note that in real life, the actual volume needed may differ from this calculated value due to factors such as measurement error and the non-ideal behavior of solutions.
Similar Questions
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