Data Analysis for Weeks 1 and 2 Lab Handout

Before answering the following questions, read the modified lab handout and watch the corresponding videos (links provided below).  These videos contain information that you will need to complete the data analysis for both weeks 1 and 2. If you have any questions, your lab instructors will be available during your regular lab time via Zoom. They will send their Zoom Meeting ID through the Portal.

Lab final questions will be based on post-lab questions!

Links to Videos: (You may need to copy and paste link into browser)

Video 1: Week 1 Revisited: 

https://www.loom.com/share/13f68e1fc676428886923fed36eec8e1

Video 2: Experimental Procedure Part 1

https://www.loom.com/share/7b5615bac47942c7b183f96f25141f71

Video 3: Experimental Procedure Part 2

https://www.loom.com/share/f413cfdf0ced4ce8a5530053d13a2427

Video 4: Week 2 Data Analysis

https://www.loom.com/share/0007cf5d0cfa4ec883c1e4a86d2159fd

Week 1 Post-lab

Watch Video 1 to revisit Week 1 and answer the following questions.  You may type your response into the space provided. You may insert photos of your work when necessary.

1) Provide any safety information regarding the chemicals encountered in this experiment.

2) Calculate the mass of NaOH required to make 100.0 mL of a 0.200 M NaOH solution. 

3) What is a primary standard? What are the characteristics of a primary standard? What primary standard was used in this experiment?

4) Calculate the mass of KHP required to neutralize 20.0 mL of 0.0995 M NaOH.

5) Based on the information provided in Video 1, fill in the data table below. Be sure to include the correct number of significant figures for each. 

Table 1: Standardization of NaOH
	Trial 1	Trial 2
mass of KHP (mKHP)
moles KHP (nKHP)
moles of NaOH (nNaOH)
initial burette reading (Vinitial)
final burette reading (Vfinal)
molarity of NaOH ([NaOH])
Average [NaOH]

Show your work below:

6) Would the measured concentration of NaOH be smaller, unchanged, or larger than the actual value if a student did not wait for KHP to completely dissolve before performing the titration? Explain your answer.

7) Based on the information provided in Video 1, fill in the data table below. Be sure to include the correct number of significant figures for each. 

Table 2: Titration of HA
	Trial 1	Trial 2
Volume HA (VHA)
initial burette reading (Vinitial)
final burette reading (Vfinal)
Volume  NaOH (VOH)
moles of NaOH (nNaOH)
Concentration of HA
Average [HA]

Show your work below:

Week 2 Post-lab

Watch Video 2, Video 3, and Video 4 pertaining to the procedure and data analysis for Week 2 and answer the following questions.  Data for Week 2 is provided on the Portal!

1) Describe how the pH of solution changed during the potentiometric titration. Did the pH change at the same rate throughout?  If not, why???

2) Plot pH verses volume of NaOH and insert the two pH plots here, one for each trial.

3) Calculate the derivative of each pH plot and insert the two ?pH/?V plots here.

4) From your derivative plots and subsequent interpolation, fill in the data table. 

	Trial 1	Trial 2
Volume end point (VOH)
Concentration of Unknown A based on VOH
Average concentration of Unknown A
pH at end point
Halfway point (V1/2)
pH at halfway point
pKa of Unknown A
Average pKa
Identity of Unknown A

5) Compare your average concentration to the concentration in week 1.  How well do they compare? Which do you think is more accurate and why?

6) Was the pH = 7 at the endpoint?  Why or why not?

7) If the pH probe was not properly calibrated and read 0.2 pH units high each time, how would this affect the measured concentration of unknown acid?  How would it affect the measured pKa?   (Note: we are asking if the measured values are smaller, larger, or unchanged and why.)

Week 3 Post-Lab 

Make sure you have read handout and watched video before proceeding to post-lab!

1)What is a buffer solution and how does it work?

2)When making a buffer, why do you want approximately equal concentrations of weak acid and conjugate base?

3)Which of the following solutions would make a buffer? If not, why?

HF/ NaF      H2SO4 / KHSO4   NaHSO4/Na2SO4   K2HPO4 / KH2PO4 H3PO4 / Na2HPO4

4)Which of the following acids (listed with pKa values) and their conjugate base would be best to make a buffer with a pH of 8.10? Explain.

HC7H5O2, pKa = 4.19

H2SO3, pKa = 1.77

HClO, pKa = 7.54

HCN, pKa = 9.31

HNO2, pKa = 3.34

5)In the data table below, list the experimental values concentration of acetic acid (Unknown A) and pKa from Week1-2 post-lab. Calculate the mass of sodium acetate required to make 40.0. mL of a buffer with target pH = 4.70.

Avg concentration weak acid [Acetic Acid] (mol/L)
Avg pKa  (Acetic Acid)
Mass of sodium acetate (g)

Show work to determine the mass of sodium acetate:

6)In the data table below, list the concentration of NaOH from Week 1-2 post-lab. Calculate the theoretical buffer capacity, in mL of NaOH. That is, calculate the volume of NaOH required to raise the pH by +1.  Determine the measured buffer capacity.

Avg concentration of strong base [NaOH] (mol/L)
Theoretical buffer capacity (mL NaOH)
Measured buffer capacity (mL NaOH)
% error

Show your work for calculating theoretical buffer capacity.

7) If the conjugate base salt used to make the buffer was wet when massed out, would the resulting buffer’s pH be too large, too small, or unchanged, compared to the target pH? Explain