Article in English: Make up three to four concentrations of one solution. Using a spectrophotometer, measure the absorbance of one concentration of solution at a given wavelength. Start with the lowest concentration of solution and move to the highest. The order isn’t important, but keep track of which absorbance goes with which calculation. Using the values obtained from the spectrophotometer, plot each point on a line graph. For each individual value, plot the concentration on the X-axis and absorbance on the Y-axis. Draw a line between each of the points. If the measurements are correct, the points should form a straight line indicating absorbance and concentration are proportional to Beer’s Law. To calculate the slope of the line you take rise divided by run. Using two of your data points, subtract the X- and Y-values from each other, then divide Y/X.  The equation for the slope of a line is (Y2 - Y1)/(X2 - X1). The point higher on the line is given the subscript 2, while the lower point is given the subscript 1. For example: The absorbance at a .2 molar concentration is 0.27 and at 0.3 molar is 0.41. The absorbance values are Y-values, while concentrations are X-values. Using the equation for a line (Y2 - Y1)/(X2 - X1) = (0.41-0.27)/(0.3-0.2) = 0.14/0.1 = 1.4 is the slope of the line. The final step to calculating molar absorptivity with data points is to divide by the path length. The path length is the depth of the cuvette used in the spectrophotometer. Continuing our example: If 1.4 is the slope of the line and the path length is 0.5 cm, then the molar absorptivity is 1.4/0.5 = 2.8 L mol-1 cm-1.

Summary in Vietnamese:
Đo cường độ ánh sáng truyền qua bằng các dung dịch có nồng độ khác nhau. Vẽ đồ thị nồng độ và độ hấp thụ. Xác định hệ số góc của đường chuẩn qua các điểm dữ liệu. Chia hệ số góc của đường thẳng cho độ dày truyền qua (chiều dày của cuvet) để có độ hấp thụ mol.