Question

question 3 12.5 pts is it possible to determine the molar absorptivity of a compound from the graph below? no. a second plot is needed with a second set of concentration values. yes. the absorptivity can be determined from the slope of the curve if the length of the cuvette is known. yes. the absorptivity is the slope of the line. no. the percent transmission is needed to determine the absorptivity.

Explanation:

Step1: Recall Beer - Lambert Law

Beer - Lambert law is \(A=\epsilon lc\), where \(A\) is absorbance, \(\epsilon\) is molar absorptivity, \(l\) is the path - length (length of the cuvette), and \(c\) is concentration. If we plot \(A\) vs \(c\), the equation of the line is \(y = mx\) (since when \(c = 0\), \(A=0\)). Here, \(y = A\), \(x = c\), and \(m=\epsilon l\).

Step2: Analyze the options

• Option 1: No. A second plot is needed with a second set of concentration values. This is incorrect. One plot of \(A\) vs \(c\) is sufficient if \(l\) is known.
• Option 2: Yes. The absorptivity can be determined from the slope of the curve if the length of the cuvette is known. Since \(m = \epsilon l\) (slope of \(A\) vs \(c\) plot), then \(\epsilon=\frac{m}{l}\).
• Option 3: Yes. The absorptivity is the slope of the line. Incorrect, because \(m=\epsilon l\), not \(\epsilon\) itself.
• Option 4: No. The percent transmission is needed to determine the absorptivity. Incorrect. Beer - Lambert law uses absorbance (\(A =-\log T\)), but once \(A\) is plotted vs \(c\) and slope is known (along with \(l\)), \(\epsilon\) can be found.

Answer:

Yes. The absorptivity can be determined from the slope of the curve if the length of the cuvette is known.