1. Percent Copper in Brass
9/27

2. Beer’s Law
States that absorbance of light is directly proportional to the concentration.
A = abc
A = absorbance (unitless)
a = molar absorptivity (M-1*cm-1)
b = path length (cm) (1 cm for our cuvettes)
c = concentration (M)
Takes the same form as y = mx +b (b should be zero)
The slope of the line m = ab

3. Reacting brass with concentrated (15.8M) Nitric Acid
Video demo for those that missed this part.
For concentrated nitric acid the equation is:
Cu(s) + 4HNO3(aq) ——> Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
Dilute nitric acid produces NO instead.
3Cu(s)  +  8HNO3(aq)  ——>  3Cu(NO3)2(aq)  +  2NO(g)  +  4H2O(l)

4. Creating a graph in Google sheets
Open your school google account and click on sheets.
Enter the data for Part 1, pre-lab question 6.
Watch and follow along with the video. I will walk around and help you during class.
Add the equation to the line with the r2 value.
R2 is a measure of how well the statistical data fit a statistical model (the line of regression). A value of 1 indicates the line of regression is a perfect fit. A value of zero indicates the line does not fit the data at all!

5. Lab Write up due Oct. 6th
Can be created in either word or google documents.
If created in google documents, you must download the document as a word file and upload that file into the Turn-it-in drop box on Moodle.
A word about Plagiarism. Turn-it-in runs your report against others that are submitted and anything that can be found on the internet. I will NOT grade your report if I find that any part of the purpose, conclusion, answers for the pre/post-lab, and error analysis, make a direct match.

6. Writing procedures in past tense…
Make them brief and state exactly what YOU did in the lab. If there were modifications to the lab (and there were- conc. of nitric acid, a volume of 250ml vs. 100ml) you must report this. Do not copy directly from the lab.
Example:
1. The mass of the brass shell was found using an analytical balance and was recorded as g.
ml of conc. nitric acid was added to the brass shell in a 250 ml beaker and was allowed to react over the weekend. Observations and calculations for how this volume were obtained are shown below.
3. 50 ml of water was added to the blue solution and was transferred to a 250 ml volumetric flask. Deionized water was added to bring the total volume to 250 ml and the flask was inverted several times.