1 The cuvettes we used in this experiment have a pathlength

1. The cuvettes we used in this experiment have a pathlength of 1.0 cm, and that is the most common size for solution work. However, 0.1 cm pathlength cuvettes are available. Would you expect these narrower cuvettes to be more useful to measure solutions of high concentration or low concentration? Explain your choice. Hint: absorption spectrometers become unreliable at absorbance values greater than 1.5 2. You could have determined the extinction coefficient (e)of copper(l) sulfate with just one data point and of ? Beer\'s law. Why would you bother to do a whole series of concentrations like this in order to calculate the value

Solution

1) In most spectrophotometric determinations, the cuvette chosen has a length of 1 cm. However, 0.1 cm cuvettes are also available and may find use under appropriate circumstances. Beer’s law states that the absorbance (A) of a solution is directly proportional to the path length (l) of the solution when the concentration of the solution is fixed. The relationship is expressed as

A = *C*l

where C is the concentration of the solution and is the path length of the solution.

When C is constant, a smaller value of l (changing l from 1 cm to 0.1 cm) will produce a smaller absorbance. This is due to the fact that the light passes through a narrower cuvette which contains fewer sample molecules and hence, light interacts with fewer molecules and produces a lower absorbance. For low values of C, the value of A reduces significantly and can be practically ignored. Hence, the optimum path length is chosen as 1 cm which allows for a practical value of A even when C is low.