Homework Help: Chem

Posted by Unknown on Tuesday, February 22, 2011 at 4:19pm.

I'm confused with Determining the concentration of a soution: beer's law lab.

1.Explain why pure water is set for a transmittance of 100%.
- I believe the pure water is set for a transmittance of 100% in order to for a tranmission relative to water

2. Explain why red light was chosen for studying these nickel solutions. What would happen if you selected the green light?
-Red light has shorter wavelenths but more frequency and thus is able to pass through nickel solutions.

3. If pure water has a transmittance of 100%, why does it have an absorbance of zero?
- I'm confused with this question that how can water have an absorbance of zero

Chem - DrBob222, Tuesday, February 22, 2011 at 11:02pm
1. You are close to being right if not exactly correct. You want to measure the transmittance of the sample (which happens to be dissolved in water). So you set the solvent at 100% transmittance so that the reading with the sample will be that due to the material being determined.

2. Absolutely not for two reasons (and red light has LONGER wavelength than green light). Samples absorb the solor that is the COMPLEMENT to their color. If the sample is green, you want to use a red filter so that the green sample will absorb as much of the red light as possible. Using green light means the sample absorbs almost nothing (because it transmits green). That's why it's green.
3.Absorbance = log(1/T)
If %T = 100%, then T =1.00
A = log(1/1) = log 1 = 0

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