What factors affect the intensity of color

Variables to be studied

WavelengthConcentration

ColorColor

Need to study in this order

Wavelength

RedOrange

Yellow

Green

Blue

Indigo

Violet

ROYGBIV

700 nm 450 nm

Refraction of Light

The bending of light as it passes from one medium to another

Investigate Wavelength• For each of the three colors, pick 10

wavelengths from 400-760 nm and measure %T keeping concentration the same.

• Recalibrate 100%T at each wavelength

• Check the filter lever

Spectronic-20Spectrophotometer

Adjust the monochromator control (1) to the set the desired wavelength on the wavelength dial (2). There may be a filter lever (8) on the lower left of the instrument. Set it to the appropriate wavelength range.

Spectronic-20

Adjust the monochromator control (1) to the set the desired wavelength on the wavelength dial (2). There may be a filter lever (8) on the lower left of the instrument. Set it to the appropriate wavelength range.

Insert the reference cuvette into the sample holder, matching up the index line on the sample holder with the index line or label on the cuvette. Adjust the 100%T control (6) to set the needle to exactly 100%T on the transmittance scale.

Remove the reference cuvette and check the zero. Adjust the 0.0%T control if necessary. Repeat calibration steps until the zero and 100%T are set and stable. Check the zero and 100%T every 15–30 minutes or anytime you change the wavelength.

Fill the sample cuvette one-half full with solution and insert the tube into the sample holder. Read the percentage transmittance directly from the transmittance scale to ±0.1%T.

Ensure that the sample holder (5) is empty. Set the instrument zero by adjusting the 0%T control (3) to set the needle to exactly 0.0 %T on the transmittance scale (4).

Ensure that the sample holder (5) is empty. Set the instrument zero by adjusting the 0%T control (3) to set the needle to exactly 0.0 %T on the transmittance scale (4).

Insert the reference cuvette into the sample holder, matching up the index line on the sample holder with the index line or label on the cuvette. Adjust the 100%T control (6) to set the needle to exactly 100%T on the transmittance scale.

Spectronic-20

1. Adjust the monochromator control (1) to the set the desired wavelength on the wavelength dial (2). There may be a filter lever (8) on the lower left of the instrument. Set it to the appropriate wavelength range.

 

2. Ensure that the sample holder (5) is empty. Set the instrument zero by adjusting the 0%T control (3) to set the needle to exactly 0.0 %T on the transmittance scale (4).

 

3. Insert the reference cuvette into the sample holder, matching up the index line on the sample holder with the index line or label on the cuvette. Adjust the 100%T control (6) to set the needle to exactly 100%T on the transmittance scale.

4. Remove the reference cuvette and check the zero. Adjust the 0.0%T control if necessary. Repeat steps 2–4 until the zero and 100%T are set and stable.

 

5. Fill the sample cuvette one-half full with solution and insert the tube into the sample holder. Read the percentage transmittance directly from the transmittance scale to ±0.1%T.

 

6. Check the zero and 100%T every 15–30 minutes or anytime you change the wavelength.

Review

Investigate Concentration

• Prepare 4-5 solutions of known concentration for each dye solution (given burettes, 25 mL volumetric flasks and a stock solution of known concentration)

• How will you pick which wavelength you should use?

A note on Spectrophotometric theory

Ι

ΙT

%100T% Ι

Ι

Transmittance T:

Dilution Calculations

Given:[blue food dye] = 1.334 10-5 M

 Using normal laboratory glassware, how will you prepare 5 solutions with concentrations between 5.3 10-7 M and 1.3 10-5 M