science chemistry

what is the purpose of using deinonized water to adjust the Spec 20 to 0 absorbance?

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  1. The glass from the vial and the DI water either reflect or absorb some energy in the Spec 20 so you adjust the instrument to 100% with a "matched" vial containing water (the usual solvent in many Spec 20 procedures). Then we assume that the absorbance of the sample vial is due to the sample and not to the solvent or the vial.

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  2. You need a reference solution. Frankly, deionized water is usually not specified in this teaching machine, rather distilled water. If you wish to learn something, let it warm up 5 min, calibrate it with deionized water, set the absorbance and transmittance, then put a sample of deionized water and Measure the absorbance. Now try it with tap water.

    Theoritizally, if ions were present in distilled water, more energy would be absorbed by those ions compared to H2O molecules (of course, there are ions in pure water...), so the absorbance calibration might be off.

    As a practical matter, there are greater errors on this measurement with this machine. (are there any fingerprints, or any oils on the sample tube?)

    Thanks for asking.

  3. oops, after calibrating with deionized, put DISTILLED in it to compare.

  4. well we did a lab with Ni(NO3)2.6H2O with 5 other solution and we got DI water by itself and put it in the spec 20 and set it to zero so when we put the other solutions they would be measured by the DI water alone. But i don't get why we have to set the DI water to zero

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  5. Read Bob Pursley's answer again. I assume zero means zero absorbance units. 100% T is the same.You need a reference. What do you think would happen if you turn on the machine, someone twists the knob, and the machine reads 50%T? Now you measure your sample. Will the absorbance (or %T) be accurate?

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  6. Ohh ok thanks sorry didn't quite understand but i do now

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