1.You make single wavelength absorbance measurements for two solutions containin

Question

1.You make single wavelength absorbance measurements for two solutions containing an absorbing analyte at concentrations C1 and C2 producing absorbance readings A1 and A2. Since C1 in known, the concentration of the unknown, C2, can be calculated. Using Beer's Law, show algebraically why it is not necessary to know wither the molar absoptivity () or the pathlength (b) to calculate C2, presuming the same cuvet is used.

2. In question 1, the unknown concentration was determined using ratio calculation. However, in the experiments we have done thus far in this class, absorbance measuremnets are made at several concentrations and a calibration plot prepared. Why is it better to generate a calibration plot than to perform a determination using a single measurement for a standard solution?

3. Solve the following set of linear equations to determine x and y

13 = 5x + y

-7 = x - 3y

Explanation / Answer

1)

According to Beer's law ,

A = Cb

where = molar absoptivity

          C = concentration

          b = pathlength

Since we are using the same cuvet b is constant also the solute is the same its molar absoptivity is same.So is also constant.

So A C ( & b are constant )

for two solutions of varing concentrations A1 / A 2 = C1 / C2

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