Experiment 16.1

For one of your indicator trials, determine the concentration of the sodium hydroxide solution you prepared. Show your calculation below.

(0.342g KHP)*(1 mol KHP/ 204.22 g KHP)=0.00167 mol KHP: 1:1 ratio; 0.00167 mol NaOH 0.00167 mol NaOH/ 0.0163 L NaOH= 0.103M

According to the Version 003 literature paper assigned: In your own words, what was the purpose of the study reported?

According to Version 003 literature paper assigned the purpose of the study reported is to compare traditional lab experiences and outcomes with students to the new TTA approach and its experiences and outcomes. The purpose of integrating TTA into a normal titration lab for general chemistry students is to provide the students with more realistic experience and engaging experience that will more likely mimic professional practices. This was observed in the study to see if it benefitted students, as much and if not more than traditional laboratory titration and to look at newly developing forms of active learning. TTA allowed for students to generate their own labs and practices with the guidance of an instructor. Overall, this open ended form of a lab was observed to see if chemistry could become more engaging and exciting for students, as well as to increase student success.

When approaching the equivalence point during the titration in Parts C and E, how should you adjust your titration technique? Explain.

As the equivalence point is being approached during titration, the rate of titrant added is slowed down in order to produce more accurate results. Once titration is even closer the titrant is added drop by drop, this is continued until the solution becomes light pink for 10 seconds.

According to the Version 003 literature paper assigned: What aspects of this study related to the studies in CHEM102L? Explain in detail the correlation between our studies and those reported

Aspects of this study related to the studies in CHEM102L are the in-depth knowledge of the experiment required before performing it. In the study, students had more freedom than students in the CHEM102L course, however both students needed to have an in detail understanding of the chemical background and procedure in order to perform the lab. The clearest consistency between the study and the CHEM102L course is the discussion after the experiment. Both sets of students were required to go in-depth with the experiments and discuss failures, successes, errors, and general observations. The biggest difference between the students in the study and CHEM102L students is that students from the study were able to choose their own dilutions and solutions.

Based on your understanding, which method of titration, using an indicator or pH sensor, provides a more accurate measurement of the sodium hydroxide concentration? Why?

Based on my understanding from Experiment 16.1 the pH sensor method of titration is the more accurate measurement of the sodium hydroxide concentration. This is specifically seen when looking at the percent error being 4% when compared to colorimetric indicators titration percent error of 6%. This can also be attributed to the fact that the pH sensor uses quantified numbers that come from the produced curve and has a larger sample size, this method is significantly more objective. Whereas colorimetric indicator is based off of color and has a smaller size, making it more subjective.

Procedure

Experiment 16.1 was the titration and identification of an unknown acid. The sodium hydroxide solution was prepared by combining 150 mL of H2O, 5.0 M NaOH (250 mL), and additional H2O that reached a final volume of 500 mL. A burette was then set up by rinsing it with 5 mL of NaOH. A scintillation vial of KHP was then obtained to prepare the KHP solution, this process utilized mass by difference to produce 4 solutions. Phenolphthalein was then added (2 drops) into the KHP flasks, which was then used to calculate the volume of NaOH, as the final step for titration preparation a stir bar was added. The titrant was added in 2-3 mL increments, until it was approaching the endpoint (3 mL away,) where the stop clock was put to 180 degrees to add fractional drops until a light pink color maintained for 10 seconds and the final volume of the titrant was recorded. Next a Vernier GoDirect pH Sensor was calibrated for use, by setting it up with pH 4 and 10 buffers. The pH probe was clamped to an Erlenmeyer flask and then was placed into the KHP solution + stir bar. The titrant (NaOH) was then added into the KHP solution, until the pH changed by 0.3-0.5 and the volume was the recorded, as 3 mL of the predicted volume was approached the titrant was added dropwise. Finally, as the pH went above 8, larger drops were added until the pH was above 11, the data was collected and the waste was disposed of.

Purpose

In this experiment the end point is being determined through the combination of acid base titration and indicators, as well as looking at acid base reactions and their stoichiometry. The titration procedure will be compared to a standard to look at its success, and the pKa and molar mass are determined as well, throughout the experiment. Overall, the above is being done in order for the equivalence point of this titration to be determined through the pH probe, to determine if the titration was successful.

Complete the following calculation. How much of a 0.5 M NaOH solution would you need to prepare a 350 mL solution of 0.1 M NaOH solution?

M1V1=M2V2 (0.5MNaOH)(V1)=(0.1M NaOH)(0.350 L) V1=0.07 L

Determine the concentration of the sodium hydroxide based on the amount of the sodium hydroxide solution that you added to the 1-L polyethylene bottle.

M1V1=M2V2; (5.0M)(5.0mL)=(x M)(250mL); 0.10 M

Explain how to mass by difference. Why do you use this method in this experiment?

Mass by difference is a repetitive process consisting of weighing the solid sample before its taken out of its container and its weight after. These two values are subtracted to find the mass by difference. This is used because it is the most accurate way to obtain the true mass.

According to the Version 003 literature paper assigned: What was the advantage of using TTA as reported by the authors?

The advantages of TTA as reported by the authors were increased engagement in general chemistry lab and knowledge, as well as providing students with an introduction to laboratory planning and methodology. Utilizing TTA also was shown to provide practice for students to engage in scientific storytelling.

In this experiment, you will be using two different physical changes to determine the end point of the titration at the same time; a color change in an indicator and the inflection point in a pH titration curve. Using the pre-lab reading and your CHEM 102 knowledge, which technique do you think would yield the more precise measure of the equivalence point and the correct sodium hydroxide concentration? Explain

The inflection point in a pH titration curve is the most accurate way to determine the end point of titration because it allows for the end point to be quantified from the numbers produced throughout the curve and multiple volumes are collected. Observing a color change in the indicator can become very subjective and can differ from eye to eye and only 3 different volumes are collected. Using the titration curve allows for the results to be more objective.