The Spec 20 Begins!

• Sunlight is Electromagnetic Energy

• Light travels in wavelengths

• Wavelength: the distance from crest to crest • Wavelength is measured in nanometers

Notice the difference in Wavelength

Why is the Ocean Blue?

UV

Fig. 10-6

Visible light

InfraredMicro-waves

RadiowavesX-raysGamma

rays

103 m1 m

(109 nm)106 nm103 nm1 nm10–3 nm10–5 nm

380 450 500 550 600 650 700 750 nm

Longer wavelengthLower energyHigher energy

Shorter wavelength

What color is this?

The spec 20

Fig. 10-8

Galvanometer

Slit moves topass lightof selectedwavelength

Whitelight

Greenlight

Bluelight

The low transmittance(high absorption)reading indicates thatchlorophyll absorbsmost blue light.

The high transmittance(low absorption)reading indicates thatchlorophyll absorbsvery little green light.

Refractingprism

Photoelectrictube

Chlorophyllsolution

TECHNIQUE

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How does the Spec 20 work

• The Spec 20 is used to measure the concentration of a solute in a solution

• Compares the absorption and the transmittance

• The higher the concentration, the higher the absorption and the lower transmittance

How do you work the Spec 20

• You must BLANK!

• Blank is to eliminate the water from the solution.

• What should the BLANK read?• ____ absorbance • ____ transmittance

• Blank should read:• 0 absorbance and• 100% transmittance

What is the optimum wavelength?

• optimum wavelength: wavelength of light the substance ABSORBS the MOST.

Measuring the Optimum Wavelength

• Set machine to wavelength you want to test.

• Blank the machine using water to eliminate the solvent.

• Measure the absorbance and record.

Re-test for each Wavelength!!

• Retest for each wavelength, increasing by 10 nm increments.

• The optimum wavelength is the one with the greatest absorbance.