Question

Using Buffers

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Version 42-0134-00-02

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Exercise 1: Using Buffers

Data Table 1. Adding 0.1M HCl from D1 into A1.

Drop Number	pH of Solution
1	8.0
2	8.0
3	8.0
4	8.0
5	8.0
6	8.0
7	8.0
8	8.0
9	8.0
10	8.0
11	8.0
12	8.0
13	8.0
14	8.0
15	8.0

INSERT A PICTURE OF YOUR PH STRIPS WITH THE ARRAY OF COLORS YOU FOUND. I WOULD LIKE TO VERIFY THAT YOU WERE READING THE RESULTS CORRECTLY.

Data Table 2. Adding 0.1M NaOH from D6 into A6.

Drop Number	pH of Solution
1	8.0
2	8.0
3	8.0
4	8.0
5	8.0
6	8.0
7	8.0
8	8.0
9	8.0
10	8.0
11	8.0
12	8.0
13	8.0
14	8.0
15	8.0

Data Table 3. Adding 6M HCl from Pipet into B1.

Drop Number	pH of Solution
1	6.0
2	8.0
3	6.0
4	6.0
5	6.0

Data Table 4. Adding 6M NaOH from Pipet into B6.

Drop Number	pH of Solution
1	8.0
2	8.0
3	8.0
4	8.0
5	8.0

Data Table 5. Adding 0.1M HCl from D1 into C1.

Drop Number	pH of Solution
1	4.0
2	4.0
3	4.0
4	4.0
5	4.0

Data Table 6. Adding 0.1M NaOH from D6 into C6.

Drop Number	pH of Solution
1	10
2	10
3	10
4	10
5	10

INSERT A PICTURE OF YOUR PH STRIPS WITH THE ARRAY OF COLORS YOU FOUND. I WOULD LIKE TO VERIFY THAT YOU WERE READING THE RESULTS CORRECTLY.

Questions

Part A

What are the similarities and differences between the data in Data Tables 1 and 2? Explain how the data supports the role of a buffer.

Part B

What are the similarities and differences between the data in Data Tables 3 and 4? Explain how the data supports the role of a buffer.

Part C

Explain how the data from Data Tables 1 and 2 are similar and different from the data in Data Tables 3 and 4. What does this indicate about a buffer’s ability to maintain pH when an acid or a base is added?

What do the data in Data Tables 5 and 6 show about the ability of water to behave as a buffer? Considering the definition of a buffer, elaborate on your answer.

Part D

In the procedures for Part C, “Adding Dilute Concentrations of Acid and Base to Distilled Water,” would it be useful to repeat procedures 2 and 3 but instead use concentrated NaOH and HCl? Explain why or why not?

Part E

One beaker contains 10.0 mL of acetic acid/sodium acetate buffer at maximum buffer capacity (equal concentrations of acetic acid and sodium acetate), and another contains 10.0 mL of pure water. Calculate the hydronium ion concentration and the pH after the addition of 0.25 mL of 0.10 M HCl to each one. What accounts for the difference in the hydronium ion concentrations? Explain this based on equilibrium concepts; in other words, saying that “one solution is a buffer” is not sufficient.

H₃O⁺_(aq) + C₂H₃O₂^-_(aq) ⇄ HC₂H₃O_2(aq)   +H₂O

K_a of acetic acid = 1.8 x 10^-5

Acetic acid/sodium acetate buffer: Acetic acid = 0.1M, Sodium acetate = 0.1M

Answer 1

Although you have not mentioned D1 or A1 or concentration or type of solutions.

Part A

What are the similarities and differences between the data in Data Tables 1 and 2? Explain how the data supports the role of a buffer.

1. In data table 1, we are adding acidic solution while in table 2 we are adding base.

However the pH of buffer was maintained showing the capacity of buffer to resist pH change on additon of small amount of acid or base

Part B

What are the similarities and differences between the data in Data Tables 3 and 4? Explain how the data supports the role of a buffer.

In data table 3, we are adding acidic solution while in table 4 we are adding base.

However the pH of buffer was maintained showing the capacity of buffer to resist pH change on additon of small amount of acid or base

Part C

Explain how the data from Data Tables 1 and 2 are similar and different from the data in Data Tables 3 and 4. What does this indicate about a buffer’s ability to maintain pH when an acid or a base is added?

Answer: In Table 1 and 2 we are adding acid and base of low concentrations while in table 3 and 4 we are adding acid or base of high concentration.