Experiment #3 report form instructions

Download the *.pdf form from the lab website and open it using Adobe 7.x or newer (we strongly recommend you update to the latest version available by going to the Adobe website). Fill in and print the form using Adobe Reader or Adobe Acrobat. If you are unsure what to put in a field, hover your cursor over the field and read the tooltip for additional instructions.

With the exception of attaching your generated calibration curve, do not attach any additional pages. Refer to the appendices in your lab manual for instructions on how to properly complete the sections in this report form. You will be required to hand write the sample calculations sections.

Procedure: appropriately reference the procedure as detailed in your lab manual.

Data: fill in the provided tables with your in-lab and calculated values, and set appropriate units for the values using the drop-down menus provided.

Sample calculations: provide a sample set of calculations under the headings provided. Only one example calculation needs to be shown for each heading (you do not need to provide an example calculation for each of the sample measurements). Due to the limitations of pdf forms, there is no option to insert digital equations. Write out your calculations by hand in the spaces provided after printing. All of the calculations you will need to perform are mentioned in this report form.

Discussion: generate a discussion by following the guidelines in the appendix, discussing your results (and what they indicate), and the indicated discussion points in the Report section of the lab manual for experiment 3.

Conclusion: provide a concise (one sentence) conclusion as indicated in the lab manual.

References: properly cite the appropriate references for this report form as detailed in your lab manual.

Calibration curve: print off a copy of your calibration curve and include it as part of your submitted report. Ensure that you have properly labelled the figure (see the appendices) and that it legible.

This page is not to be printed. Do not add this page (1) to the print range.

How much is zit?

1

Experiment #3: How much is zit?

Introduction

Although titrations are an effective quantitative method for determining the amount of a chemical in a sample, they can be tedious to perform and frequently rely on the human eye to determine an endpoint. By using ultraviolet/visible (UV/Vis) spectroscopy, it is possible to relate the amount of absorbance in a sample of visible or near visible light to the concentration of a particular chemical in a more accurate manner than the naked eye. The absorbance and concentration of a sample are related by the Beer-Lambert law (equation 1):

The Beer-Lambert law relating concentration to absorbance 𝐴𝐴 = 𝜀𝜀𝑏𝑏𝑏𝑏 (1)

Where A is absorbance, ε is the molar extinction coefficient, c is the concentration, and b is the path length of the cell.

By generating a calibration curve of absorbance and known concentration, the absorbance of an unknown sample can be determined from its absorbance. In this experiment, the amount of salicylic acid in a sample of acne cleanser was determined by forming a complex with iron. The iron complex is highly coloured and absorbs at 535 nm, and a calibration curve was generated using standard solutions of salicylic acid.

Procedure1

B

How much is zit?

2

Data

Table 1: concentration of salicylic acid in standards and unknown solutions.

Solution Concentration of salicylic acid ( )

Table 2: measured UV-Vis absorbance values of solutions. Sample or standard Absorbance at

Sample Calculations

Concentration of salicylic acid in standard #

Equation of the line relating concentration to absorbance (from the trendline of Figure 1)

B

How much is zit?

3

Example set of calculations for the relation of absorbance to % weight of salicylic acid in the acne cleanser (values are from sample measurement # )

Concentration of salicylic acid in the Stock Unknown Solution

Number of moles of salicylic acid in the 50.00 mL volumetric flask

Number of moles of salicylic acid in 1.00 mL of acne cleanser

Number of grams of salicylic acid in 1.00 mL of acne cleanser

B

How much is zit?

4

Percent weight of salicylic acid in 1.00 mL of acne cleanser

Average, standard deviation, and relative standard deviation between the unknown sample calculations

Average % weight of salicylic acid in 1.00 mL of acne cleanser

Standard deviation in the average % weight

Relative standard deviation in the average % weight

B

How much is zit?

5

Comparison of the average % weight to the advertised % weight B

How much is zit?

6

Discussion B

How much is zit?

7

Conclusion

References

B