Pre-Lab Questions 1. a. What is the difference between absorbance (A) and transm

Question

Pre-Lab Questions 1. a. What is the difference between absorbance (A) and transmittance (T)? b. What is the proper way to handle a cuvette for use in a spectrophotometer? Why are these steps important for analysis? 2. When two solutions are combined, the concentration of each compound is diluted due to the addition of the other solution. To determine the diluted molarity of a compound, the following equation can be used: M1 represents the original molarity of a solution, V1 represents the volume of solution before the dilution, M2 is the diluted molarity, and V2 s to total volume of the new dilute solution (not the volume of additional solution added). Using this equation, calculate the diluted molarity of 100 mL of a 0.5 M solution when 50 mL of water has been added.

Explanation / Answer

1)

(a) Transmittance is a directly measurable quantity whereas absorbance must be calculated using the transmittance measurement.

Transmittance is a measurement of the amount of light passing through the sample, but absorbance is a measurement of the amount of light absorbed by the sample.

Absorbance (A) = log(I0/I)

Transmittance (T) = I/I0

(b) A cuvette is a kind of laboratory glassware, usually a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or optical grade quartz (for UV light) and designed to hold samples for spectroscopic experiments. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading.

(2) M1V1 = M2V2

=> 0.5 x 100 = M2 x (100+50)

=> M2 = 0.33 M

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