Review of Stoich and Lewis Structures Intro

This week we worked on reviewing the stoichiometry that we had learned in order to prepare for our test. We white boarded problems from our different stoich worksheets to review mass percent, empirical formulas, yield, and limiting reactants. We also did an in class online quiz to practice doing math without a calculator. There is  a lecture on doing no calculator math on the moodle  which can be accessed here.

We learned that the key to doing no calculator math is forgetting about significant figures and using whole numbers. This method is only used for the multiple choice portion of the test, so when you have found the rounded answer you are able to pick the real answer with proper significant figures. The answer given and your calculated answer will probably be different, but you just have to pick the answer that is the  closest to what you got. We also took 3 moodle hot pots in order to prepare for the multiple choice portion of the test. These quizzed us on masses and the mole, chemical equations and stoichiometry, and stoichiometry applications.

 

On Wednesday we had our first AP chemistry test which included a no calculator multiple choice section and a calculator free response section. Overall many people did very well on one portion  of the test and not so well on the other portion. For me personally, I did well on the free response portion of the test and not so great on the multiple choice portion. I think this is because I only did the hot pots once and I also did them the night before the test. I think I would have benefited more from these hot pots if I had done them multiple times and done it sooner than the night before the test.

 

The  last two days of the week were spent learning about Lewis Structures. These were introduced by a  POGIL. We learned that these were diagrams that showed the element symbol in the middle with dots around the outside to represent the valance electrons. This POGIL helped to show the class how these structures are drawn to represent atoms and molecules. It focused on the idea of covalent bonding which is where two atoms share electrons. This POGIL showed us the octet rule which is where atoms  gain or lose electrons so that they have 8 valance electrons. When drawing a Lewis structure, you must make sure that every single element has eight valance electrons. The only exception is with Hydrogen, it only forms a duet of valance electrons because it only needs two electrons to fill its valance shell. There were also 2 lectures and a lecture quiz on Lewis structures.

Over all this week, I think that I had an okay test. This is because I did really good (96%) on the free response and worse(73.33%) on the multiple choice. I'm planning on working on no calculator math and I'm going to go in after school and look at my multiple choice test to see what I got wrong.  I also think that my knowledge about the Lewis Structures is still improving. I have a good understanding of the basic rules, but I'm still not quite sure about the diagrams when it comes to compounds that are more complicated. For this reason I would give my understanding a 7/10.

Limiting Reactants,Yield and Empirical Formulas

This week in class we talked about limiting reactants, yield and empirical formulas. We learned that in some chemical reactions there are not unlimited amounts of both of the reactants. In order to figure out the reactant that is limiting the reaction, we used a type of stoichiometry.

To view the lecture on limiting reactants click here. 
 Limiting Reactants Steps:
Step 1: Write out the mass of one of the reactants
Step 2:Do a times and a line and bring down grams. It should be 1 mol/molar mass.
Step 3: Do a times and a line and bring down moles. use the mole ratio between the reactant and the product.
Step 4: Do a times and a line and bring down moles of the product. It should be molar mass/ 1 mol
Step 5: Multiply all of the numerators together and divide by all of the denominators.
Step 6: Repeat steps 1-5 for all other reactants. Compare all of the results and find the smallest amount of product. This means that this is the reactant that is limiting the reaction.

To learn about limiting reactants in class we did a POGIL called Limiting and Excess Reactants.

The next thing that we learned this week was percentage yield. We talked about the difference between theoretical yield and actual yield.  Theoretical yield is what you are suppose to get from a reaction and is found by performing calculations. It is the largest amount of product that is possible to create from a given amount of reactant.  It is very rare to get 100% of yield in real life. This is where actual yield comes in. Actual yield is the measured amount of a product produced during a reaction from a given amount of reactant. Click here to see the lecture on yield.

Percentage Yield Steps:
1. Balance the equation.
2. Find the limiting reactant for the chemical reation.
3. Find the theoretical yield.
4. Divide the actual yield by the theoretical yield and multiply by 100. 

Our last topic this week was empirical formulas and mass percent. We learned that an  empirical formula is a formula that is the simplest ratio among the elements of a compound.

 Empirical Formulas:
1. Take the percents of the the elemental analysis and change them to grams by assuming that the total is out of 100 grams.
2.Multiply the grams of an element by 1mol/ molar mass. repeat for each element in the compound.
3.  Divide the answers by the lowest answer.
3. Round all other answers to nearest number, unless a common fraction like 1/2, 1/3, 2/3, 1/4 is in the decimal. If this happens multiply all of the subscripts by the numerator of the fraction to get the empirical formula.

To determine the molecular formula from the empirical formula we divide:
molecular molar mass/empirical molar mass

This number is then used as a scale factor for the empirical formula and is multiplied by all of the other subscripts.


We did an Empirical Formulas POGIL in class to better help us understand this concept.

Mass Percent:
To find the mass % of an element you multiply the number of that type of element by its atomic mass and then divide by the formula weight of the compound. Finally multiply by 100.

To find the mass % of a component we learned that you take the mass of the component divided by the total mass of the substance.Finally multiply by 100.

Over all I felt that I understood the material well. I would give my understanding of this week's material a 9. I'm giving this rating because I was able to understand it well enough to be able to help others also understand. I also only gave it a 9 because I'm still learning everyday and I don't think that I know every single thing  about this topic, but I do have a good understanding of the basic concepts.

I liked how we did white boarding in class this week because it helps me to make sure that I'm doing problems correctly. It is also a good way to collaborate between table partners and share ideas about problems.

Concentration, Molarity, Absorbance, Transmittance

This week in class we focused on the concept of concentration and using Molarity.We learned that Molarity is the moles of a solute divided by L of the solution.

We also talked about absorbance and transmittance and how they are related to concentration. We talked about how Beer's Law relates absorbance to concentration: A=KC where A is the absorbance and K is the constant of 130,000 M^-1 cm^-1 and C is the concentration. We learned through our experiment that the more concentrated a solution is the less transmittance it will have.

 To do some more investigation about concentration, we did a lab with Blue #1 dye. In this lab we learned how to dilute a stock solution of Blue #1 by mixing together a certain number of milliliters of the stock solution with a certain number of milliliters of water. 

 For example  my group did 6/4 would mean 6mL of the stock solution and 4 mL of water and 1/9. 

Here is the link to the Blue #1 Lab Procedure which will detail more information about the lab and post lab questions.

Blue #1 Lab

We then learned how to operate a colorimeter, which is a device that sends a certain wavelength of light into the liquid to measure its absorbance. The dye that we were using is blue because the solution is allowing the blue light to pass through it. In order to measure the absorbance we used the wavelength of red light (635nm) because red is the furthest away from blue on the visible spectrum of light.

We placed the dilutions of the stock solution, and the gatorade and powerade into the colorimeter to figure out the absorbance of each of the solutions. From the stock solution we were able to as a class make a calibration curve for absorbance vs. concentration.

By using the equation provided by the calibration curve we were able to figure out the concentration of Blue #1 in the powerade and gatorade.

We figured out that the concentration of blue #1 in gatorade is 1.1 micromolar and the concentration in the powerade was2.8 micromolar.

From here we were able to use dimensional analysis to determine the concentrations of Blue #1 that would be in 500 mL of each drink.

Over all I think that this lab helped me to gain a better understanding of the relationship between molar concentration and absorbance. I liked being able to take one reading from the colorimeter and then being able to use that number to figure out absorbance and then from that number to figure out concentration. I like when we are forced to work through things on our own because I feel like I learn better when this happens. In particular when we had to do calculations on our own at home I really liked that.

I feel that I would give my understanding of the material a 7.5/10. This is because I feel that I understand the major concepts but I'm still having problems setting up problems that deal with this content. The last 3 questions on the lab made me think very hard and I had a difficult time figuring out what equation to use for question 1 (see Blue #1 lab under post lab assessments), even though it was an M1V1=M2V2. My group also had a hard time figuring out the grams of Blue #1 in  500 mL of the two drinks.  It was just hard to piece the calculations together with the information we were given. I feel that this is something that I need to work on, so that I can get to the point where I can do these types of problems with ease.

I'm now curious if the concentration of  different colored dye in other types of  gatorade and powerade  is the same as or different as the concentration of Blue #1 in the gatorade or powerade.