Week of 9/23/13

Back to the blog.

This week was a test week in all but one of my classes, so I didn’t study for the Chem test as well as I should have (excuses, excuses). The test was on everything I covered in the last blog post, so I won’t go over it again.

However, there were some HotPot quizzes provided by the good doctor, and next time I should actually do them. Apparently there was a small correlation between people who studied with those quizzes and people who did well. 

(I’m not seeing it) 

Studying is something I've never been good at, and I've trained myself to learn and retain the knowledge the first time to make up for that. However, when I fail to do that I end up with a horrible score (it’s always hit-or-miss). Mr.Oleksinski will tell you all about it. I intend to study ahead for this next unit.

After the test, we started on the bonding unit. Lewis Dot Structures are the first thing we’re working on. Lewis dot structures (named for Gilbert N. Lewis) are simply a way to draw a molecule with it’s bonds, representing valence electrons with dots and two valence electrons as a line (if two atoms connect with it).

If you want to draw a Lewis Dot Structure, put the more electronegative ion in the center. You then make sure that the ions you’re putting on the outsides have eight valence electrons, unless they can be stable with less. 

We've only just started the bonding unit so I can't (officially) tell you more. Sorry.

Week of 9/16/13

This past week has been all about stoichiometry. Stoichiometry is the study of numbers in chemical equations.
So the past week was spent doing various combinations of finding limiting reactants, finding masses of reactants and products. Generally, in the problems we've worked on, one reactant is in excess and one is limited. In the real world, this is often the case, because having an excess of one (usually very common) reactant makes the reaction go faster.



We also messed with empirical formulas, the simplification of a chemical formula, Thus making C6H3 into C2H. Empirical Formulas are for finding the simplest isomer of a molecule. However, this does not mean C6H3 is the same as C2H, or that they share similar properties, but it does mean these elements have the same ratio of masses. In order to find an empirical formula, you must first find the molecular ratios of your chemical reaction. Then you simply reduce and simplify your equation as much as possible.

Yield was a simple matter. Given a chemical equation, an unlimited amount of one reactant, and a certain amount of a different reactant, you should be able to figure out how much of the products you are able to make. However, you should also know how to find the reactants when given the yield (products).

Finding mole ratios was harder for me. You use a mole ratio diagram to convert the reactants and their coefficients to masses, and then use those masses to find the mass of a product. You don’t need to deal with Avagadro’s number, but the method provided is a little complicated.

This past week hasn't been too hard for me, but I feel that I might have missed some details for not paying enough attention in class. We did a lot of POGIL activities, and I have very smart people in my group to help me when I don't get something. Mole ratios with "the bridge thing" especially went over my head. So I know what to study here. We also have a test this Thursday, so I have to hit the books pretty hard.

...At least it's not String Theory.

Week of 9/9/2013

This past week, I learned about the mole and it’s relevant measurement molarity. It's a pretty large part of stoichiometry. A mole is the number of atomic mass units needed to make a gram of hydrogen. Molarity is a measurement of  the number of moles in a liter, similar to density. We were introduced to the colorimeter, an instrument used to measure color absorption.


The colorimeter's operation was simple enough, but (as always) it was important to go over equipment operation procedures before class. The cubettes it uses require careful handling to get accurate results. First we use water to calibrate the colorimeter, by putting dihydrogen monoxide in a cubette and inserting the cubette into the colorimeter.

We began the lab with two popular sports drinks: Powerade and Gatorade. Both use the dye “Brilliant Blue FCF” (C37H34N2Na2O9S3) for color (providing experimental consistency), making the two ideal for a lab. To begin the lab, we measured the (635 hz) absorption of BBFCF in various mixtures of stock solution and hydrogen hydroxide.

The procedure was simple: fill cubettes with designated stock/H2O mixture and write down what the colorimeter put out.

Class Results (Stock/H2O):

Stock:H2O ratio	Concentration (M)	Absorption (test 1)	Absorption (test 2)	Absorption (test 3)
10:0	7.5	1.062	0.968	1.104
8:2	6.8	0.824	0.873	0.765
6:4	4.5	0.567	0.531	0.435
4:6	3.0	0.427	0.412	0.435
3:7	2.3	0.347	0.328	0.370
2:8	1.5	0.152	0.229	0.150
1:9	0.75	0.063	0.100	0.098
0:10	0	0	0	0

We then tested the Gatorade and Powerade (among 14 groups) in the colorimeter to see its absorbance.

Various Group Results (Power/Gatorade Absorption Results):

Powerade Absorption	Gatorade Absorption
0.405	0.140
0.374	0.140
0.366	0.125
0.386	0.141
0.312	0.147
0.389	0.138

We had to calculate the molarity of both sports drinks, using the methods presented to us earlier in the week. In my opinion, this was the most confusing part, I still don’t fully understand it. I hope to have this figured out before the test.

After all this was done, we compiled our data in our journals to find a few things. We put our data in a graphing program (or Excel) and got a formula:
y = 0.1367x - 0.0102

This would come to help us later in the experiment.

In this lab I learned how to conduct a lab (this being my first in this class) and how to operate a colorimeter. I learned how to format my lab journal and submit a flowing lab report. I learned how to properly compile various data into a graph in the specified format and how to come up with an equation for it. We used this equation to find molecular absorption later in the lab.