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Homework answers / question archive / Submission page for Performance task 3 As you read through the lab, answer the following questions: Qualitative relationships: What is the relationship on the amount of transmitted light vs absorbed light concerning:    a) Thickness of the container (tube)?    b) Concentration of the sample?    c) Color of the sample?    d) The specific chemical in the solution? Quantitative Relationships between absorbance  vs wavelength:       wavelength Absorbance of sample A Absorbance of sample B            400 nanometers              0

Submission page for Performance task 3 As you read through the lab, answer the following questions: Qualitative relationships: What is the relationship on the amount of transmitted light vs absorbed light concerning:    a) Thickness of the container (tube)?    b) Concentration of the sample?    c) Color of the sample?    d) The specific chemical in the solution? Quantitative Relationships between absorbance  vs wavelength:       wavelength Absorbance of sample A Absorbance of sample B            400 nanometers              0

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Submission page for Performance task 3

As you read through the lab, answer the following questions:

Qualitative relationships:

What is the relationship on the amount of transmitted light vs absorbed light concerning:

   a) Thickness of the container (tube)?

   b) Concentration of the sample?

   c) Color of the sample?

   d) The specific chemical in the solution?

Quantitative Relationships between absorbance  vs wavelength:

      wavelength

Absorbance of sample A

Absorbance of sample B

           400 nanometers

             0.173

         0.600

           420 nanometers

             0.202

          0.451

           440 nanometers

             0.282

          0.050

           460  nanometers

             0.650

          0.310

           480 nanometers

              0.920

          0.522

           500 nanometers

              1.150

          0.750

            520 nanometers

              1.230

           1.10

            540 nanometers

               0.885

            1.21

            560 nanometers

               0.458

             1.32

580 nanometers

               0.300

             1.15

600 nanometers

               0.066

             0.90

What is your independent vs dependent variables?

Graph both sets of data on the graph paper below:

The color of the solution can be determined by the lowest absorbance for that wavelength. (remember, these wavelengths are in nanometers vs meters from your electromagnetic spectrum)

What would be the color of Solution A?

What would be the color of Solution B?

Determining the absorbance of known concentrations for Solution A:

What is the most sensitive wavelength for Solution A (meaning highest absorbance) ______.  Using this wavelength, we now place known concentrations of Sample A in the Spec 20 machine and see the absorbances.

      Sample A concentrations

Absorbance using Spec 20 instrument

    0.000Molar (distilled water)

           0.000

           0.020 Molar

           0.150

           0.050 Molar

           0.382

           0.100 Molar

           0.550

           0.150 Molar

           0.950

           0.200 Molar

           1.230

 

What is the independent & dependent variables?

What variables go on what axis?

Graph the sample concentrations vs the absorbances on the graph paper below:

Does this a direct or inverse relationship?

Is this graph more linear or nonlinear?

Determining the concentration of an unknown sample using the standard curve from above.

 

   Last initial

Unknown #

Absorbance

Concentration from the graph

054, 799, 119

   A-6

     0.800

 

760, 563, 219

   N-2

     0.720

 

823, 015, 094, 329

   L-5

     0.650

 

317, 491, 556, 585

   Y-4

     1.150

 

168, 181, 968, 036

   T-8

      0.850

 

790, 193, 791, 373

   M-12

      0.960

 

 

Application question using the Spec 20 machine:

You want to determine if the toxic metal Lead (Pb) was in your drinking water and if the concentration was a high enough Molarity to cause health problems. Using the Spec 20 instrument, how would you set up a procedure to identify the metal and determine the concentration?

Transmittance vs Absorbance

 

 

Block the light beam with your hand to verify that the CBL responds rapidly by dropping radically in value. If it does not, check with your instructor before proceeding.

 

 

                                                  Thickness of the container

 

 

                                   meter reading ________

 


                           meter reading __________

 

                                              Concentration and Color

 

 

 

Some light is absorbed by the distilled water.

0.62

                                              meter reading _________

 

 

 

                                            meter reading __________

                            meter reading _________

 

 

 

0.29

 

 

0.68

 

 

                                     The Spec 20 Instrument



  1.  

 

 

How a Spec 20 machine works to identify a chemical

 

 

24.7: Color and the Colors of Complexes - Chemistry LibreTexts

 

Interactive Student Tutorial

 

 

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