Exp. 2 Spec Analysis Slides

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School

Pennsylvania State University, Altoona *

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111

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Chemistry

Date

Feb 20, 2024

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pdf

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7/28/2023 1 CHEM 111: Spec Analysis of Food Dye Spec Analysis Learning Objectives: 1. Measure volume using a pipette. 2. Measure absorbance using a spectrophotometer. 3. Estimate wavelength of absorbance for a colored substance using a color wheel. 4. Calculate energy of a single photon at a certain wavelength. 5. Calculate concentration of a solution being diluted from sock solution. 6. Graph data in Excel to plot data. 7. Determine concentration of a solution using a calibration curve. 1 2

7/28/2023 2 Purpose of Experiment Purpose: Determine the concentration of Yellow #5 dye or tartrazine in Mountain Dew and Mountain Lightning soda. Light (electromagnetic spectrum) The color of a substance is the result of a molecule absorbing visible light. Yellow #5 have double bonds that absorb light. Many colorful compounds contain double bonds between nitrogen atoms (N=N) called “azo groups.” 3 4

7/28/2023 3 Light (electromagnetic spectrum) What wavelength would yellow absorb? Part A. Prepare Yellow Dye Standards • Obtain 100 mL of stock solution. Record Molarity. • Pipette 2.00 mL of stock solution into a 100.00 mL volumetric flask labeled A. • Fill to 100.00 mL with deionized water and mix the solution. • Repeat steps, pipetting 5.00 mL, 10.00 mL, and 15.00 mL stock solution. 5 6

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7/28/2023 4 Part A. Using a Graduated Pipette Insert blunt end in pipette pump, scroll down with thumb to pull up liquid, use lever to dispense liquid into vessel . Part A. Filling a Volumetric Flask 7 8

7/28/2023 5 Part A. Table 1 Fill in Table 1. with volume of stock solution (amount pipetted) and total volume (100.00 mL volumetric flask). Is this the correct number of significant figures ? YES! Solution Volume of stock solution (mL) Total volume (mL) Concentration ( M ) A 2.00 100.00 B 5.00 100.00 C 10.00 100.00 Reactions in Aqueous Solution 10 Solution – homogeneous mixture composed of two parts: Solute – the substance that is dissolved (Yellow #5). Solvent – the medium which dissolves the solute (Water). The term concentration refers to the amount of solute (Yellow #5) in a given amount of solvent (Water). 9 10

7/28/2023 6 Solution Concentration 11 Molarity Molarity is the number of moles of solute dissolved in 1 liter of solution. 0.000300 M tartrazine reads as, “0.000300 molar tartrazine”. This solution contains 0.000300 mol of tartrazine per liter of solution. Molarity ( ) = n M V moles solute = liters solution Part A. Molarity There are different ways to represent the same molarity. -1 0.000300 mol 0.000300 M = 0.000300 mol/L = 0.000300 mol L = 1L 11 12

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7/28/2023 7 Diluting Solutions 13 Concentrated solution: More solute particles per unit volume Dilute solution: Fewer solute particles per unit volume Add water LESS moles per volume of water. Molarity (mol/L) decreases. Part A. Calculate Molarity Using the dilution formula, M 1 V 1 =M 2 V 2 , Show the calculations to determine the concentration (M 2 ) of Yellow #5 (tartrazine) in dilute solutions A, B, and C. M 1 V 1 =M 2 V 2 M 1 = molarity of stock solution V 1 = volume of stock solution (pipetted) M 2 = molarity of dilute solution ? V 2 = final volume of dilute solution (100.00 mL) 13 14

7/28/2023 8 Part A. Calculate Molarity Solution A: 0.000325 M stock solution (*note that this value changes each semester) ( ) ( ) ( ) ( ) ( ) ( ) 1 1 2 2 - 2 2 6 2 MV = M V 0.000325 M 2.000 mL = 100.00 mL 0.000325 M 2.000 mL = 100.00 mL = 6.50 ×10 M M M M Notice that the diluted solution molarity is 0.00000650 M which is a lot smaller than 0.000325 M . This is because adding water made the Yellow #5 less concentrated. Part B. Preparing Cuvettes • Label and fill cuvettes (test tubes) with solutions, the two soda brands, and one with deionized water (“blank”). 15 16

7/28/2023 9 Part B. Analyzing Solutions • Set the spectrophotometer to 375 nm. • Place the deionized water blank in the spec and push “0” Abs. • Measure the absorbance of solution D at different wavelengths. Perform a blank at each wavelength. • Graph data and determine wavelength at maximum absorbance. Part B. Analyzing Solutions Pro Tip* Use a KimWipe to wipe off cuvettes before placing them in the spectrophotometer. 17 18

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7/28/2023 10 Part C. Calibration Curve • Set the Spec to the wavelength at maximum absorbance of yellow #5 determined in Part B. Perform a blank. • Measure the absorbance of solutions A, B, C, D and two sodas. Record each absorbance in Table 3. Part C. Calibration Curve A calibration curve , also known as a standard curve , is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. y = 23829x - 0.0021 R² = 1 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0.00E+00 1.00E-05 2.00E-05 3.00E-05 4.00E-05 5.00E-05 6.00E-05 Absorbance at 427nm Tartarzine (yellow #5) concentration (M) 19 20

7/28/2023 11 Part C. Calculate Concentration Calculate concentration (molarity) of sodas using the equation of the on the calibration curve. For example (* note you will have a different equation ): Y = 23829x – 0.0021 Absorbance of soda Concentration (M) ??? -5 -5 0.379 Abs = 23829 x - 0.0021 0.379+ 0.0021 = x 23829 x = 1.5993 × 10 M = 1.60 × 10 M Light (electromagnetic spectrum) The energy of a single photon of light can be calculated using the following equation. hc E = λ E = energy h = Plank’s constant 6.626 x 10 -34 J ∙s c = speed of light 2.998 x 10 8 m/s λ = wavelength of light (m) Note* In lab our spectrophotometer measures wavelength in nanometers (nm). 21 22

7/28/2023 12 Light (electromagnetic spectrum) The energy of a single photon of light can be calculated using the following equation. ( )( ) =             -34 8 -1 -19 -19 -9 6.626 x 10 J s 2.998x10 ms hc E = = 2.739997x 10 J =2.74 x 10 J λ 10 m (725 nm × 1nm hc E = λ 23

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What is the definition of spectrophotometry? A. Spectrophotometry is the study of interaction of matter with electromagnetic waves (the whole spectra) b. Spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength
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