In: Chemistry
Using the extinction coefficient of 18,000 M-1cm-1, convert A405nm data into µM of p-nitrophenol (Note the unit change from concentration to the number of moles!). Assume that the path length is 1 cm and the total volume was 4 mL
Using Excel (or similar spreadsheet program), plot µM of p-nitrophenol produced as a function of time in minutes. Draw a line of best-fit through the initial linear region of the data set. Determine the slope of this line and enter it as your answer (without units) using decimals, not scientific notation. The "natural" units for this slope are µM/min.
Time (min) | A (405 nm) |
0 | 0.012 |
0.3 | 0.025 |
0.6 | 0.036 |
1 | 0.047 |
1.5 | 0.068 |
2 | 0.085 |
2.5 | 0.103 |
3 | 0.125 |
3.5 | 0.139 |
4 | 0.158 |
5 | 0.19 |
6 | 0.23 |
7 | 0.25 |
8 | 0.27 |
9 | 0.28 |
10 | 0.29 |
Time (min) | [p-nitrophenol] (M) |
0 | 0.012/0.018 = 0.6667 |
0.3 | 0.025/0.018 = 1.3889 |
0.6 | 0.036/0.018 = 2 |
1 | 0.047/0.018 = 2.6111 |
1.5 | 0.068/0.018 = 3.7778 |
2 | 0.085/0.018 = 4.7222 |
2.5 | 0.103/0.018 = 5.7222 |
3 | 0.125/0.018 = 6.9444 |
3.5 | 0.139/0.018 = 7.7222 |
4 | 0.158/0.018 = 8.7778 |
5 | 0.19/0.018 = 10.5556 |
6 | 0.23/0.018 = 12.7778 |
7 | 0.25/0.018 = 13.8889 |
8 | 0.27/0.018 = 15 |
9 | 0.28/0.018 = 15.5556 |
10 | 0.29/0.018 = 16.1111 |
Note: According to Beer-Lambert's law: Absorbance (A) = cl
Where = molar absorption coefficient = 18,000 M-1cm-1 = 0.018*106 M-1cm-1
c = concentration of p-nitrophenol
l = parth length = 1 cm
Therefore, c = (A/0.018) M (since 1 M = 10-6 M)
Now, the plot of [p-nitrophenol] (M) versus time (min) can be drawn as follows.
The equation of the plot: [p-nitrophenol] = 1.65388*time + 1.4604
The above equation is in the form of y = mx + c, where 'm' is the slope of the plot.
Therefore, the slope of the plot = 1.65388