Analysisoffooddyesinbeverage - PreLabQuestions...

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Unformatted text preview: Analysis of food dyes in beverage Pre­Lab Questions The visible absorption spectrum for FD&C Blue 1 is shown in Figure 6. The estimated concentration of the dye was 7.0 μM (7.0x10­6 M) 1. What would be an optimum wavelength for measuring the absorbance versus concentration of a series of FD&C Blue 1 dye solutions? Explain your answer. Absorbance measurements are most accurate and sensitive in the range 0.2 ­ 1.0. answer: The optimal wavelength for measuring the absorbance versus concentration of a series of FD&C Blue 1 dye solution is 635 nm (630 nm­ 640 nm). On the visible light spectrum, this wavelength represents the color orange, which is the light that blue solutions absorb. 2. To construct a calibration curve, a series of known concentration standards is prepared. Using the estimated concentration of the FD&C Blue 1 stock solution, determine the concentration of each of the following dilutions. Hint: M1V1=M2V2 dye stock solution (A) B C D E F G H Concentration(Micromolar, μM) 7.0 μM 5.6 4.2 2.8 2.1 1.4 0.7 0 water (mL) 0 2 4 6 7 8 9 10 Stock Solution(mL) 10 8 6 4 3 2 1 0 μ answer: M1V1=M2V2 concentration of B = (7.0 μM)(8 mL)/10 mL = 5.6 3. Using the information provided in Question 1; predict the absorbance of each solution A­H at the optimum wavelength. Refer to Equation 3 in the Background section. The value of ε is 130,000 M­1 cm­1 . answer: A= εbc A B C D E F G H Absorbance (Predicted) .910 .728 .546 .364 .273 .182 .091 0.0 Introductory Activity data table: solutions stock (A) B C D E F G H water(mL) 0 2 4 6 7 8 9 10 stock solution(mL) 10 8 6 4 3 2 1 0 concentration 0.643 0.527 0.410 0.286 0.164 0.144 0.075 0 #8,9, and 10 Guided­Inquiry Design and Procedure 1. Based on the graphs obtained in the Introductory Activity, identify the optimum linear relationship or calibration curve for quantitative analysis of the concentration of an “unknown” solution containing FD&C Blue 1 food dye. answer: Based off of the graphs obtained in the Introductory Activity, the optimum one to use is the ­logT vs Concentration calibration curve. 2. Which graph would provide the most accurate means to determine the concentration of the “unknown” solution whose transmittance has been measured spectroscopically? Explain in terms of Beer’s law and give an example of how the analysis would be carried out. answer: The graph that would provide the most accurate means to determine the concentration of the “unknown” solution whose transmittance has been measured spectroscopically is the ­logT vs Concentration calibration curve because it is linear and the equation used is A= εbc 3. Consult the ingredients label for a blue­colored sports drink or other consumer beverage. Identify the dyes that are present and explain whether the beverage can be analyzed using the calibration curve described above. answer: Our choice of beverage that was used for this part of the experiment was Gatorade. After consulting the ingredients label, the only food dyes present in the sports drink was Blue 1, the same dye that was used to create the calibration curve described above. Therefore based off of the information that was collected in the Introductive Activity, it is possible to analyze the this beverage because it contains the same dye used in this experiment. 4.Obtain the necessary spectroscopic data for the beverage containing FD&C Blue 1 food dye. Recall that absorbance measurements are most accurate in the range of A values from 0.2 to 1.0. Treat the beverage sample if needed to make sure the data is in the acceptable range. answer: the spectroscopic data for the beverage containing FD&C Blue 1 food dye was about 0.161. 5. Determine the concentration (micromolar, μM ) of the dye in the beverage and calculate the amount (mass) of dye in milligrams per liter of the beverage. The molar mass of FD&C Blue 1 is 793 g/mol. answer: The concentration of the dye is: ​0.161/130000(1)= 1.2e­6 μM ​. For this calculation we’ll be using the base form of the concentration, which is ​0.0000012​, and instead of using ​Molarity​ we will convert it to ​moles/liter​. The amount of mass of dye in milligrams per liter is: 0.0000012 FD&C Blue 1 1 ​mole 793.0 FD&C Blue 1 1 gram 1 Liter 1 ​mole (0.0000012 mole/L FD&C Blue 1)(793.0 g/mole) = ​9.5e­4 g/L After this, all that’s left to do is convert it to mg/L. This is done by: (9.5e­4 g/L)(1000mg/1g)= ​0.95 mg/L AP Review Question 1. Calculate the value of % T for an absorbance value A = 1.5. Using this result, explain why absorbance measurements >1 may not be accurate. answer: ­logT=1.5 > logT=­1.5 > T= 10^(­1.5)=0.316 > %T= (T)(100)=​31.6 The reason why absorbance measurements > 1 may not be accurate is because the percent transmittance will be close to 100. If this is the case, than that means that the light passing through isn’t being absorbed. Spectrophotometric studies can be conducted on any colored compound. The transition metal group of the periodic table exhibits a wide array of different colored compounds. The complex ion tetraamminecopper(ll) contains four ammonia molecules covalently bonded to a copper (II) ion. In aqueous solution, Cu2+ ions will bond to four water molecules in a square planar geometry. The ion is a light blue color. The water molecules can be displaced by ammonia molecules, which are stronger Lewis bases than water. The appearance of the intense dark blue­violet color of the [Cu(NH3)4] 2+ ion is often used as a positive test to verify the presence of Cu2+ ions. 2. Write a balanced chemical equation for the reaction of copper(II) sulfate and concentrated ammonia to produce tetramine copper(II)sulfate. answer:​CuSO4(aq) + 4NH3(aq) ­­> Cu(NH3)4SO4(aq) 3. [Cu(NH3)4] 2+ solutions exhibit a deep blue­violet color. How can you use spectrophotometry to confirm that this reaction has occurred and that the product formed is in fact tetraamminecopper(lI)sulfate. Would you expect the wavelength of maximum absorbance (λmax) for Cu(NH3)4 2+ to be greater than or less than λ max for Cu(H2O)6 2+? Explain. answer:​The wavelength of Cu(NH3)4 2+ is less than λ max for Cu(H2O)6 2+. Thus it absorbs the shorter wavelength yellow light, this is why it has a deep blue color. 4. The electron transitions responsible for the colors of transition metal ions involve transitions. Why are zinc ions colorless in aqueous solution? answer:​Zinc is an element in the d­block which forms colourless ions in aqueous solution.The zinc ion has a full set of d sub­shells but not classed as transition element, therefore it's properties are not the same as the transition elements which have coloured properties. Summary Considering that at this point into the school year everyone is quite familiar with doing labs, this lab wasn’t difficult or long. The point of this lab was to use spectroscopy and graphical analysis to determine the concentration of dye in a sports drink. Luckily for us, the sports drink chosen for this experiment had only one dye in it, FD&C Blue 1, and this dye happened to be the one used in the lab. Despite that, using Excel to create and analyze the graphs weren’t as easy as we initially thought it would be.At first glance it seemed like an easy concept to grasp, but a few difficulties, like placing the correct information in the right places, using the correct data for the graph and our group losing our data for the graph due to technical difficulties, caused us to lag behind, but in reality nothing goes as plan and getting help from the instructor made these problems trivial. I also neglected to mention that instead of using a spectrophotometer, we used a colorimeter, which as a result, gave us the desired data for the graph needed for the experiment right away. It might be because of this that calculating the %T, T, 1/T, logT and ­logT values was such an easy task, but I digress. All in all, due to us using the the food dye FD&C Blue 1 in the Introductory Activity and us using a blue sports drink, which also had FD&C Blue 1, in the Guided­Inquiry, we were able to easily compare the data in the Guided­Inquiry to the data charts in the Intro and use the information as basis to determine if the data we gathered was accurate. ...
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