Spreadsheet #15: Colorimetric Titration
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A series of solutions are prepared with
identical amounts of colored dye and increasing amounts of chlorine titrant. The chlorine oxidizes the dye in a molar
ratio of 1:1, resulting in a proportional loss of color. The results in a
linear decrease in absorbance of the analyte (dye)
until it is all consumed. Plot this data and determine the intercept for
the x-axis which represents the end-point of the titration. Display a
best-fit line on your chart that clearly shows the x-intercept. Report the concentration of the dye in
micromoles/Liter. (Click to download the data set: 15-titra.)
|
Cl2 Added |
Abs. |
Slope: |
. |
|
(umole/L) |
|
y-Intercept:
|
. |
|
0 |
0.821 |
R^2 |
. |
|
1 |
0.772 |
. |
. |
|
2 |
0.687 |
. |
. |
|
3 |
0.641 |
[Cl2] at x-axis intercept: |
|
|
4 |
0.587 |
____ |
uM |
|
5 |
0.502 |
|
|
|
6 |
0.463 |
||
|
7 |
0.385 |
||
|
8 |
0.331 |
||
|
9 |
0.279 |
||
|
10 |
0.204 |
||
|
11 |
0.158 |
||
|
12 |
0.078 |
||
|
13 |
0.019 |
||
|
14 |
0.000 |
||
|
15 |
0.000 |
||
|
16 |
0.000 |
||
|
17 |
0.000 |
||
|
18 |
0.000 |
||
|
19 |
0.000 |
||
|
20 |
0.000 |
||
|
Excel Programming Tips: |
|
To calculate the slope,
intercept, and R2 for the descending values, be sure to select
only the appropriate (non-zero) absorbance data for your calculations. Use these results to calculate your best
fit line for the chart. |
|
Simply adding a trendline from the Excel menu does not accurately display the desired best-fit line in this case. Create your own data set in the spreadsheet by inserting another column and calculating a “synthetic” best fit line using the slope and intercept values calculated above (y=mx+b). Add this column as a new data set on the chart and format it so only the line shows, and not the individual data points. |