Preparation and properties of buffer solutions lab answers

Preparation and Properties of Buffers – Results and Discussion Guide for Laboratory Report

Results Section: Include the assigned tables in your results section. Be sure to include sample calculations below each table, as appropriate. Note that you should show only one example calculation for each type of calculation encountered.

Discussion section: Incorporate the topic, discuss and answer the assigned questions in your discussion section

Part 1: Preparation of a Buffer from a Weak Acid/Base and Its Conjugate

1. Results Section: Complete and insert the following table into your lab report under the results sections. Label the table appropriately as found in the lab manual (pages 9-13). If the actual amounts of the weak acid/base and its conjugate used during the preparation differ from the calculated amounts, compute the new target pH.

Be sure to mention the table in the text prior to it appearing in the report.

Target pH

Measured pH

% error

Buffer

2. For Discussion section: What are some likely sources of error for the preparation of the buffer?

Part 2: Properties of Buffered and Non-buffered Systems

1. Results Section: Complete and insert the following table into your lab report under the results sections. Label the table appropriately as found in the lab manual (pages 9-13).

Using your measured pH values, calculate the concentration of H+ (M) in beakers 1 and 3, before and after the addition of HCl.

Initial [H+] (M)

[H+] (M) after addition of HCl

By what factor did the [H+] (M) increase?

Beaker 1 (0.1 M NaCl)

Beaker 3 (Buffer)

1. Results Section: Complete and insert the following table into your lab report under the results sections. Label the table appropriately as found in the lab manual (pages 9-13).

Using your measured pH values, calculate the concentration of H+ (M) in beakers 2 and 4, before and after the addition of NaOH. Organize your answers in a table as shown below.

Initial [H+] (M)

[H+] (M) after addition of NaOH

By what factor did the [H+] (M) decrease?

Beaker 2 (0.1 M NaCl)

Beaker 4 (Buffer)

2. For Discussion section: Incorporate this topic, discuss and answer this in your discussion section. Which system (buffered or non-buffered) shows a smaller increase/decrease in the concentration of H+? Explain.

3. Results Section: Complete and insert the following table into your lab report under the results sections. Label the table appropriately as found in the lab manual (pages 9-13).

For each beaker, calculate the expected (theoretical) pH when 5.00 mL of 0.0100 M HCl or 5.00 mL of 0.0100 M NaOH is added to 20.0 mL of buffered and non-buffered systems. Use the actual volume of acid/base added in the calculation. Organize your answer in a table as shown below.

Actual volume of acid or base added (mL)

Measured pH

Calculated (Theoretical) pH

% Error

0.1 M NaCl + acid (beaker 1)

0.1 M NaCl + base (beaker 2)

Buffer + acid (beaker 3)

Buffer + base (beaker 4)

Include this part only if it was done

Part 3: Preparation of a Buffer Using One Component (Optional)

1. Results Section: Complete and insert the following table into your lab report under the results sections. Label the table appropriately as found in the lab manual (pages 9-13).

Target pH

Measured pH

% error

Buffer

Buffer + acid (beaker 1)

Buffer + base (beaker 2)

2. For Discussion section: Incorporate this topic, discuss and answer this in your discussion section. What are some likely sources of error for the preparation of the buffer and the addition of acid/base?

3. Post-Lab questions: Can be found on the next page. Print it out and fill it out by hand, or type in the answers and print out. Attach to the back of your lab report for grading.

Name:__________________________ Date:____________________

POST-LAB QUESTIONS-Preparation and Properties of Buffers:

1. What is the effect on the pH of the solutions in beaker 1 and 3 if the pipet was rinsed with DI H2O but not conditioned with the HCl solution?

2. Which of the following pairs of solutions will produce a buffer solution? Explain your reasoning.

a. 10.0 mL of 0.10 M HCl + 10.0 mL of 0.10 M NaOH

b. 10.0 mL of 0.10 M HCl + 5.0 mL of 0.10 M NaOH

c. 10.0 mL of 0.10 M HF + 10.0 mL of 0.10 M NaOH

d. 10.0 mL of 0.10 M HF + 5.0 mL of 0.10 M NaOH

3. A student prepared 50.0 mL of “Buffer Q” using 0.50 moles of HA and 0.50 moles of A- while another student prepared 50.0 mL of “Buffer S” using 0.25 moles of HA and 0.25 moles of A-.

a. Do the two buffer solutions have the same or different pH? Explain.

b. If 1.00 mL of 0.010 M NaOH were added to the two buffer solutions, would the pH of the two solutions increase or decrease? Explain.

c. Which solution (Buffer Q or Buffer S) would show a smaller change in the pH for question (b)? Explain.

CHEM 120B: Buffers-Results and Discussion Guide for Laboratory Report, Summer 2016 Page 1 of 5

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