Labreport#7 - Colorimetric Determination of a Food Dye C PDF

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Colorimetric Determination of a Food Dye C...

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General Chemistry SCC 201 Professor, Sharmila, Shakya Lab Report # 7 Colorimetric Determination

Objective To determine color of elements, we speak of light that is emitted of each element of specific wavelengths. Electrons that are excited absorb light and jump to higher energy orbitals. This movement is also called transition. Thus those electrons are unstable; they will readily fall back to a lower energy state and emit the excess energy of light. The light that produces wavelengths is not the color absorbed but the complementary color of the wavelength that were not absorbed. Color plays an important role in our response to food and how food appeals to us. In our experiment we prepare quantitative dilutions of FD&C Blue No. 1 food dye, to determine the wavelength of maximum absorption using a spectrophotometer to measure the absorbance of each solution. Finally we will determine the concentration of dye in a commercial beverage. At the end of our process we will calculate the frequency and energy associated with radiation of the wavelength we measured, using Beer’s law A = ɛ bc. Also we calculate the concentration of dye in each tube using the dilution formula. MiVi = MfVf

Materials Equipment

5 x cuvets, laboratory film ( Parafilm), spectrophotometer Chemicals

Distilled water, FD & C Blue No. 1 dye

Method A. Preparing Quantitative Dilutions A. Use FD & C Blue No.1 dye as provided and distilled water to measure the required amount of dye stock and water in the cuvets. Make sure all cuvets are dry and to label each cuvet with the required solution. Cover the cuvets with laboratory film (Parafilm TM) or use cork. Don’t shake solution, because bubbles could interfere with the measurements. Cuvet # FD & C Blue No. 1 dye Distilled water

0 0 5.00

1 1.00 4.00

2 2.00 3.00

4 4.00 1.00

5 5.00 0

B. Calculate the concentration of dye in each cuvet using this formula: MiVi = MfVf Make sure to pay attention to significant figures. And the final volume in all tubes should be the same at the end. B. Determining Optimum Absorbance Wavelength 1. Warm up the spectrophotometer for at least 20 min, than set the instrument to the first measurement wavelength of 510 nm. 2. Now use cuvet 0 as the blank (the blank is the solvent the sample is dissolved in), zero the spectrophotometry in Absorbance mode. It removes the absorption due to the solvent and the cuvet from the sample measurement. 3. Insert cuvet 5 and measure and record the absorbance. 4. Repeat step 1-3 for the all other wavelength: 530, 570…etc. Re-zero the instrument with cuvet 0, before each wavelength change. C. Analysis of commercial Beverage 1. Now, insert cuvets 1-5 sequentially and record the absorbance on your data sheet. You don’t have to re-zero between measurements since you are measuring at the same wavelength. 2. Obtain a sample of a commercial beverage and record the brand on your data. Transfer approximately 5 mL of the sample to a clean, dry cuvet and record its absorbance at the same wavelength. 3. Determine the concentration of FD & C Blue No. 1 dye in the commercial beverage sample graphically (show on the graph) and also using the equation of the line.

Data and Calculations Part A: Cuvet # 0 1 2 3 4 5 Cuvet # FD & C Blue No. 1 dye Distilled water

Dye Concentration, M 0 1 x 10ˉ5 2 x 10ˉ5 3 x 10ˉ5 4 x 10ˉ5 5 x 10ˉ5 0 0 5.00

1 1.00 4.00

2 2.00 3.00

4 4.00 1.00

5 5.00 0

# 1 Cuvet: MiVi = MfVf

5.00 x 10ˉ5 x 1 mL = Mf x 5 mL

# 2 Cuvet: MiVi = MfVf

5.00 x 10ˉ5 x 2 mL = Mf x 3 mL

# 3 Cuvet: MiVi = MfVf

5.00 x 10ˉ5 x 3 mL = Mf x 2 mL

# 4 Cuvet: MiVi = MfVf

5.00 x 10ˉ5 x 4 mL = Mf x 1 mL

# 5 Cuvet: MiVi = MfVf

5.00 x 10ˉ5 x 5 mL = Mf x 0 mL

Part B: Wavelength (ᵡ) 510 530 550 570 590

Wavelength (ᵡ) 610 630 650 670 690

Absorbance 0.099 0.226 0.499 1.103 1.653

Optimum wavelength: 630 nm

Absorbance Wavelength Using Cuvet 800 700 Wavelength (ᵡ)

600 500

Absorbance Wavelength (ᵡ), nm

400 300 200 100 0

1

2

3

4

5

6

Nr. of cuvet

7

8

9

10

Absorbance 1.700 1.904 1.884 0.465 0.073

Part C: Cuvet # 1 2 3 4 5 Beverage C

Dye concentration, M 1 x 10ˉ5 2 x 10ˉ5 3 x 10ˉ5 4 x 10ˉ5 5 x 10ˉ5 6 x 10ˉ5

Absorbance 1.069 1.575 1.848 1.875 1.896 0.529

Absorbance

Analysis of Comemrcial Beverage 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0

1

2

3

4

5

6

Cuvet #

Discussion To choose the optimum wavelength for our analysis, we needed to make sure that we re-zeroed our spectrophotometer with our cuvet # 0 as our blank, to put the instrument in the zero mode. Although we re-zeroed out spectrophotometer after each use, to get a better and more guarantied result and to make sure we have the right values, we should have done this process at least 2-3 times. Our analysis shows that our absorbance was increasing, compare to our unknown beverage. We obtained 0.529 value of our unknown beverage, which shows us we were successful in measuring a light absorbance of this product. No other errors were found.

Conclusion Brand C was absorbed with the lowest absorbance of wavelength at the same concentration, which we assume that a detector which measured the intensity of light transmitted through our sample, was part of the reason why its absorbance was lower than the others, as well as the frequency and energy associated with radiation of wavelength.

References Miller,D.(2013) General Chemistry I Laboratory Manual.Kendall Hunt....