Thank you for visiting A 39 4 mL sample of a 0 486 M aqueous acetic acid solution is titrated with a 0 485 M aqueous sodium hydroxide solution. This page is designed to guide you through key points and clear explanations related to the topic at hand. We aim to make your learning experience smooth, insightful, and informative. Dive in and discover the answers you're looking for!
Answer :
Final answer:
The pH after 27.5 mL of base have been added is approximately 3.97.
Explanation:
In this titration, acetic acid (CH3COOH) is being titrated with sodium hydroxide (NaOH). Acetic acid is a weak acid, and sodium hydroxide is a strong base. The reaction between them is as follows:
CH3COOH + NaOH -> CH3COONa + H2O
Before the titration, we have a 39.4 mL sample of a 0.486 M acetic acid solution. This means that there are 0.486 moles of acetic acid in 1 liter of solution. To calculate the number of moles of acetic acid in the 39.4 mL sample, we can use the formula:
moles = concentration x volume
moles = 0.486 M x 0.0394 L = 0.0191 moles
During the titration, 27.5 mL of a 0.485 M sodium hydroxide solution is added. This means that there are 0.485 moles of sodium hydroxide in 1 liter of solution. To calculate the number of moles of sodium hydroxide added, we can use the formula:
moles = concentration x volume
moles = 0.485 M x 0.0275 L = 0.0133 moles
Since acetic acid and sodium hydroxide react in a 1:1 ratio, the number of moles of acetic acid remaining after the titration is:
moles remaining = initial moles - moles added
moles remaining = 0.0191 moles - 0.0133 moles = 0.0058 moles
To calculate the concentration of acetic acid after the titration, we divide the number of moles remaining by the total volume of the solution:
concentration = moles remaining / total volume
total volume = initial volume + volume added
total volume = 39.4 mL + 27.5 mL = 66.9 mL = 0.0669 L
concentration = 0.0058 moles / 0.0669 L = 0.0866 M
Now, we can use the Henderson-Hasselbalch equation to calculate the pH:
pH = pKa + log([A-]/[HA])
The pKa value for acetic acid is 4.76. Since acetic acid is a weak acid, we can assume that most of it has dissociated into acetate ions (A-) and hydrogen ions (H+). Therefore, [A-] is approximately equal to the concentration of acetic acid after the titration, which is 0.0866 M. [HA] is the concentration of acetic acid before the titration, which is 0.486 M.
pH = 4.76 + log(0.0866/0.486) = 4.76 - 0.79 = 3.97
Learn more about calculating ph during a titration here:
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