You examine the buffering capacity of three unknown solutions by conducting an e

Question

You examine the buffering capacity of three unknown solutions by conducting an experiment where you slowly add 0.01M HCl to each solution until the solution is neutralized. Phenol red is used to indicate the pH of the solution (basic, neutral, or acidic). The initial color of each solution is recorded Table 2 below. You record the amount of HCl added to each beaker to reach neutralization. Results of this experiment are below. PLEASE ANSWER 3-6 Based on the results, which of the three solutions, X, Y, or Z, is the best buffer? Explain your answer, using evidence from your own lab's results for Exercise 3. You suspect that one of the solutions contained sodium bicarbonate. Which one and why? Name one characteristic of a good buffer. In Exercise 3 of the lab, you're supposed to record the color of the solution and the pH of the solution. When do you stop recording? Why?

Explanation / Answer

Ans. #3. Solution Z is the best buffer.

A buffer is a solution that resists pH change when a small amount of acid or base is added to it. The more is the required amount of acid/base to reflect pH change, the better is the buffer.

Assuming all the three solutions to be initially at same pH, solution Z requires maximum amount of HCl to it before the end point is reached. That is, it requires maximum amount of HCl to show pH change (say, initial pH to neutralization pH of 7.0).

#4. Solution Z is suspected to contain sodium bicarbonate.

NaHCO3 dissociates into Na+ (spectator ion) and HCO3- (bicarbonate ion, conjugate base of carbonic acid).

HCO3- ions accepts H+ (donated from HCl) to form carbonic acid (H2CO3) and neutralizes the acid. Therefore, a solution containing bicarbonate ion acts a good buffer and consumes larger quantity of HCl to deflect pH change (to reach equivalent point).

            HCO3-(aq) + H+ (aq) ------------> H2CO3

#5. A good buffer requires more quantity of acid/base to reflect pH change, i.e. it resists pH range to addition of relatively larger amount of acid/base.

#6. As you reach near the end point, the addition of each drop of acid to the solution in flask shows color of neutralization for relatively longer time.

The last drop of acid, the addition of which causes the neutralization color to persist for 15-20 seconds, is consider as the end point of titration.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

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