9-30-13

This week we finished up our stoichiometry unit and had a test on Wednesday. Stoichiometry is the mass and amount relationships between reactants and products in a chemical reaction. After the test, we started learning about Lewis structures. Lewis structures are also known as electron dot diagrams. They are named after Gilbert N. Lewis who published his essay "The Atom and the Molecule" in 1916. Lewis structures are used to provide a simple way for chemists to represent molecules that allow reasonable predictions to be made about the structure and properties of the actual molecule. The properties of a molecule really depend on how the electrons are distributed throughout the molecule. http://www.chem.ucla.edu/harding/lewisdots.html (this website gives a description on drawing Lewis structures which really helped me as well).
Two methods the atom Ne could be drawn is

The diagram on the left shows the Lewis structure. The amount of dots surrounding the atom gives the core charge. For example, the atom Ne has a core charge of +10. 

Molecules can also be shown with a Lewis structure. Covalent bonds are shown by drawing lines. Covalent bonds are the sharing of two electrons in the valence shell of both atoms. 

 This diagram shows sulfuric acid and the covalent bonds connecting Sulfur and Oxygen and Oxygen and Hydrogen. Hydrogen must always share two electrons known as a bonding pair. Also, the sum of the shared or bonding electrons and the lone pair electrons for carbon, nitrogen, oxygen, and fluorine atoms must be eight (an octet). The other elements usually follow the octet rule as well.
This week, I'd give my understanding of our new subject about a 9. I think that I understand the topic well enough that I was able to help my classmates with questions that they had. I also think that doing this POGIL really helped my understanding, and doing the whiteboard activities and listening to other people's ideas really helped as well. I hope that I understand this unit better than the stoichiometry unit and hopefully do better on the test.

9-23-13

This week, we learned more about stoichiometry, limited and excess reactants, reaction particle diagrams, yields, and empirical formulas. Stoichiometry is the mass and amount relationships between reactants and products in a chemical reaction. You start with the grams given, use molar mass of the given molecule to convert it to moles of the given molecule. Then you use a mole ration from the balanced equation to get moles of the unknown molecule. Using that, you use molar mass of the unknown molecule to convert it to mass of the given molecule and get grams calculated at the end. During a chemical reaction, if there are fixed amounts of reactants to work with, one of the reactants may be used up first. This prevents the production of more products. To do this in class, we used the example of assembling a race car and having a fixed set of parts to make one race car, and there was always a part that there wasn't enough of to make an entire race car, so that was the "limiting reactant". We also learned that the reactant with the smaller number of moles isn't always the limiting reactant. It all really depends on the ratios of the reactants, and the one with the smallest ratio is the limiting reactant.
We used reaction particle diagrams to show before and afters of reactions. Theoretical yield is what you're supposed to get, and it rarely gets 100%. Actual yield is what you get (lower than theoretical) and it's the measured amount or produced experimentally. The percentage yield formula is
(actual yield/theoretical yield)X100%.
An empirical formula is a formula that represents the simplest ratio among the elements of a compound. http://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm (really explains the empirical formula).
                                                                                   

Reaction particle diagrams 

 

I really understand the stoichiometry problems and finding the limited and excess reactants. I think that I need a little more practice with empirical formulas, but I understand the idea of them and what they mean. 

9-16-13

This week, we learned about stoichiometry and the relationship between concentration of a solution and transmittance of light. Stoichiometry is the mass and amount relationships between reactants and products in a chemical reaction. In simpler terms, it refers to the relative proportion of components. It's also important for equations to be balanced. The molecules on one side of an equation must be equal to the molecules on the other side, and the masses (in both amu and grams), and the amount of moles on one side must add up to the mass on the other side of the equation. Mole ratios are the ratio of the coefficient of one molecule or formula unit in a balanced chemical equation to the coefficient of another one in the equation. I learned that in an equation such as, 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)  the mole ratio of ammonia (NH3) to oxygen is 4:5. All stoichiometric equations must have a mole ratio, otherwise they can't be completed. You can also use equations to find the amount of moles needed in a reaction. (http://www.esf.edu/efb/schulz/Stoichiometry.htm)

In class, we also did an experiment that helped show the relationship between the concentration of a solution and the amount of transmitted light that will pass through. We used blue #1 dye to make each solution. Each solution contained a certain amount of mL of the dye, and a certain amount of mL of deionized water. We also tested Powerade and Gatorade. From this experiment, I learned that the higher the concentration of the solution, the lower the amount of transmitted light. From this I learned that concentration and transmitted light are inversely related, and concentration and absorption are directly related. We used a colorimeter to get these results.

I understand the ideas we learned in class this week, especially from the lectures and the worksheets. With a little more practice on setting up the equations like those on the stoichiometry worksheets, I think I'll fully understand it.