Reference no: EM133254138

Statistical Evaluation of Acid-Base Indicators

In this experiment, each technician will be standardizing the HCl solution prepared in L03 against the standard tris base. To ensure a consistent sample, technicians will combine their solutions into several bottles, they will mix them randomly. Statistically, seven cycles of mixing are adequate to provide a uniform mixture.

This means that all technicians will titrate the same solution using the same tris base. The difference is that different groups of technicians will use different indicators. Technicians will calculate the apparent concentrations based on the observed endpoints of the experiment.

Indicator error is when the color change does not coincide with the stoichiometric endpoint of the reaction. Technicians will analyze the pooled results to see if the indicator error present is great enough to be statistically significant in our results

Additionally, we will compare technicians who used the same indicator to see if there are statistical differences in their results.
This experiment introduces you to the use of indicators and to the statistical concepts of mean, standard deviation, Q test, and t test.
You will compare the accuracy of different indicators in locating the end point in the titration of the base "tris" with hydrochloric acid:

(HOCH2)3CNH2 + H+→ (HOCH2)3CNH3 + Tris(hydroxymethyl)aminomethane "tris"

Prelab Calculation: show your complete set up (with units) in your lab manual
1) What mass of tris base (121.14 g/mol) is needed if 35 mL of 0.1M solution is titrated? This is the amount of tris that you will start with as a sample size.

2) What volume of 0.1M HCl is expected to be needed if 0.245 g tris base are used? This type of calculation is used to predict an expected endpoint. (You should always do this rough calculation before your first rough trial so that you slow the addition of titrant as you near the endpoint)

Week One: Titration of your HCl against tris base standard.

Procedure
1) Combine HCl stock solutions from L03. Obtain 7 2 L flasks. Each person in lab prepared 500 mL of solution. Three people will empty their solution into one of 3 flasks bottles. The next three students will add theirs to the same three flasks. Swirl the flasks to mix.
2) The next three students will empty their solutions into three other flasks (flasks 4-6). Now pour from the original three flasks to half fill the second set of three flasks. Swirl flasks 4-6. The remaining 3 students will empty their solutions into flask 1-3 and swirl to mix. We now have 6 flasks that contain a mixture.
3) Each student will fill their bottles with some of the solution from one of the flasks.
4) Repeat steps 1-2 three times. Rearrange student filling order to randomize as much as possible.
5) After three empty/fill cycles, the solutions should be well randomized. Students may now fill their bottles for analysis.

You will follow the outlined procedure based on your assigned indicator. As discussed in your prelab materials, there are two different types of indicator error.
a) Type 1: the indicator changed color before or after the stoichiometric requirements are met.
b) Type 2: the indicator color change is difficult to detect because our eyes are not sensitive to light→ dark changes. We will try to offset this error by choosing a direct or back titration method. Regardless of the direction, you will want to prepare your own indicator color standards for reference.
6) Prepare indicator color standards for your assigned indicator. Use a small amount of dissolved tris in a small beaker and add a drop of indicator. In a second beaker, add a small amount of the acid and a drop of the indicator.

Before you leave lab:
Calculate the average, standard deviation and % RSD for your titers. Show your calculations and results in your lab notebook. You are welcome to use the statistical function of your TI Calculator to calculate the average and standard deviation.
After Lab:
1. Correct the masses using the buoyancy correction at 23.33°C. (B was calculated in lab 01).

2. Correct your titration volumes for your buret bias (lab 01)
3. Determine the concentration of HCl that must be present in your sample.
a Direct: Based on the mass of tris reacted and the volume of HCl used, (moles HCl reacted/volume HCl used)
b Back titration: Based on mass tris used and the volume of standard NaOH used, (moles tris + mole NaOH)/volume HCl used
4. Report your retained values, their mean, their standard deviation, and the relative standard deviation (s/x) to the class discussion board. These will be used to determine the pooled data. Make certain to note the indicator that you used.

Using Excel to perform statistical analyses:
There is a playlist of videos in YouTube shown as a link in Canvas. You will watch the videos and then you will apply the statistical analysis tools in Excel to your class data set.
Collect all of the data posted by your peers into one tab of an Excel Spreadsheet as shown. Enter the data by indicator and by technician. For instance, group the same indicator results, and within an indicator, group by the technician.

Purpose:
Procedure: Reference your manual and note any specifics to your protocol and any deviations from the printed procedure.
Theory Section should include a discussion of the F test, the Grubb Test, and the t test. When and why are they used? What is a titer, and how is it used? What is a back titration? What is direct titration? What is indicator error? Data: Enter your raw data

Discussion:
In addition to analyzing your data, consider the following factors in your discussion. For each of these, discuss how they would affect the resultant mass of sample.
• What if the mass of the solid is not corrected for buoyancy?
• HCl is less concentrated than is labeled.
• What are the difficulties involved with using colored indicators?
Future Work: Based on your specific errors, what changes could be made that would allow better results?

Results:
1. What is the concentration of the HCl solution. Yours, class, average of mean.
2. Refer to table 1A. Report the average, %RSD and n for the class data.
3. Refer to table 1B. Using the Grubbs test, did any specific indicator provide data that appeared to be an outlier?
4. t-test results: Do not post the entire t-test output here. Select the numeric values needed to support your answer.
a) Is there a statistical difference between your data and the class average? Explain
b) Is any specific indicator statistically different from the others? Explain.
c) Is there a statistical difference between technicians using your indicator?
Does choice of indicator

References in APA format

Attachment:- Acid-Base Indicators.rar