Quantitative Reactions & Analysis Discussion Questions
These questions will help you complete your Smart Worksheet, so it is suggested to complete
this assignment first. Please include your properly formatted table and graph (see Data and
Graphics activity for formatting requirements), and please write your answers to the following
questions in paragraph form as needed. Submit this file as a PDF to Gradescope.
1. Make a table of your calibration curve data below (the concentration and absorbance data
points for your 4 known copper sulfate solutions) using the actual concentrations. (2 pts)
Table 1. Concentration vs. Absorbance.1
Concentration (%)
100
50
25
12.5
Absorbance
1.227
.376
.334
.149
2. Using that table, plot your calibration curve in Excel (absorbance vs. concentration) and
paste that graph here, adding a figure caption. (3 pts)
Concentration vs. Abosorbance for Cupric sulfate
1.4
y = 9.357913043x + 0.169347826
R² = 0.749544175
1.2
Absorbance
1
0.8
0.6
0.4
0.2
0
0
0.02
0.04
0.06
0.08
Concentration (M, Molarity)
Figure 1. Concentration vs. Absorbance.
0.1
0.12
3. Compare the two calculated concentrations of unknown copper sulfate solution. (5 pts)
a. Using the mass of your solid product from Part A, calculate the theoretical
concentration of the unknown copper sulfate reactant using stoichiometry.
Remember, you used 10.0 mL of the unknown solution in your reaction.
0.229 Molarity
b. Using the equation for the line of best-fit on your calibration curve, calculate the
concentration of the unknown copper sulfate solution from its absorbance.
x = .0348 M
c. Which concentration is likely to be more accurate? Explain why that method of
solving for concentration is likely to be more accurate.
The concentration given by the graph, as it is a automatically given equation,
while the other method of doing the math physically given the grams and mL can
be wrong as human error can occur, along with the amount of sig figs limiting us,
while the other can be easily gotten by adjusting the setting in the software.
4. Consider the trendline for your calibration curve. (5 pts)
a. Should we force the trendline for the plot of absorbance vs. concentration through
the origin (0,0)? Explain why or why not.
No, the reason being is that forcing it, would alter the line of best fit, as it would
be heavily biased towards the lower points on the graph instead of the higher
points that could be gotten when doing the experiment.
b. Is forcing the trendline through the origin (0,0) the same as adding the point (0,0)
to your data? Will you get the same trendline equation? Explain using the data
you collected in lab.
Adding the point (0,0) to our data, would alter the entire slope of our data and
would overall affect our trendline if we add it. Forcing the trendline through (0,0)
would make my data look very out of place for any of the higher points while the
lower points would look more in place and data points in the higher ranges would
be more as outliers then just being close to the trendline.