Prepare Solution D Prepare solution D using the following reagents. Predict the

Question

Prepare Solution D Prepare solution D using the following reagents. Predict the pH and then measure the pH Solution D: 10.00 ml of 0.2 M acetic acid and 1.00 mL, of 0.1 M sodium hydroxide, and 9.0 mL distilled water. Divide solution into two approximately equal parts: To the first part, add a few drops of HCL(exact volume is not necessary), predict the pH of the solution after the addition of HCL and record Measure and record the actual pH. To the other half add a few drops of NaOH and measure the pH If time permits you may continue to add drops of either acid or base until the buffering capacity is exceeded Address the following in the Initial Results and Conclusions Compare the initial pH of solution D to that of solution B. Can you qualitatively account for the difference? It may be helpful to write an equation showing the formation of each solution. Discuss whether or not this solution is a buffer. Explain the behavior of the solution when acid or base was added Based on the changes in pH upon the addition of acid or base, is the buffer better suited to handling one versus the other? Explain You might find it helpful to prepare a summary table, listing all solutions investigated in the entire lab exercise. Give the initial pH and the pH after addition of acid or base.

Explanation / Answer

solution D

CH3COOH + NaOH ---------------> CH3COONa + H2O

10 x 0.2 =2 1x0.1 =0.1 0 0 initial mmoles

1.9 0 0.1 - after reaction

1.9/20 0 0.1/20 concentration

The solution behaves as a buffer, its pH is calculated by Hendersen equation.

pH = pKa + log [conjugte base]/[acid]

=4.76 + log 0.1/1.9

= 3.481

When HCl is added , the pH further decreases

When NaOH is added, the pH increeases.

4.1 Compare this calculated pH with the previous question.

4.2 The solution d has the conjugate base CH3COONa and acid CH3COOh both ein solution. Thus it acts as a buffer.

4.3 When acid is added, H+ is added.

CH3COONa + H+ ------------> CH3COOH

Thus the added H+ is absorbed by the conjugate base , to give the undissociated acid

When base is added ,

CH3COOH + OH- ----------> CH3COO- + H2O

The added OH- is absorbed by the undissociated weak acid to give the conjugate base.

Thus in both cases , the pH is not affected considerably.

4.4

Based on the pH of the solution D and their concentrations, the solution is better in absorbing the base than acid.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.