Week 6 Reflection

        At the beginning of this week, we discussed empirical and molecular formulas to wrap up Unit 5. For a couple days, we worked on a worksheet to help us understand how to find these types of formulas. At first, I was confused what exactly the words empirical and molecular meant in terms of formulas, and I wasn't sure what the word empirical itself meant either. I later learned that empirical means something that is based on data. I also learned that an empirical formula is the simplest, whole number ratio of a compound, and a molecular formula is the exact formula of a compound, which would be a multiple of that compound's empirical formula. For example, the empirical formula of the zinc chloride from our previous lab was ZnCl2. If we had used twice the amount of zinc, the formula would be Zn2Cl4, which is the molecular formula of the compound. Thinking about these formulas in this way helped further my understanding of how they work, and made it easier for me to complete the worksheet we did in class. Below is a picture of some of the problems and worked out solutions on the worksheet:

Another concept from the worksheet was percent compositions of compounds. Finding percent compositions would tell us the make up of certain compounds, and how much of each element the compound is made of. For the problems on the worksheet, we were generally given the amount in grams of two or more elements in a compound, and sometimes the total mass of the compound as well. To find the percent composition of the elements, we had to divide the mass of the element by the total mass of the compound, and then multiply the answer by 100 to put the number in terms of a percentage. This part of the worksheet was very easy for me; I have been familiar with percentages in math for years now, so I understood the concept right away and knew exactly how to complete the problems. Attached is a picture of some of the percent composition problems from the worksheet:

        The day after completing our empirical/molecular formulas and percent composition worksheet, we worked on our review guide in class, and the next day we had the Unit 5 test. I think the test went well for me; I understood the concepts of moles and molar mass, as well as finding the relative mass of different substances. I also knew how to convert grams of a substance to moles, and moles of a substance to grams. I remember the test had problems where you had to find the number of particles of a substance, and I used Avogadro's number, 6.02 x 10^23, to find the answers. There were a few percent composition problems, and I had no trouble on those either. I took my time on all the problems so I could avoid making small errors, and I made sure to show all my work and used units wherever I could. My only issue on the test was with one of the empirical and molecular formula problems. The compound was made up of three elements, so I first used my conversions to find the number of moles for each element, and I got 0.2, 0.2, and 0.3. If I simplified these numbers down further, my ratio would be 1:1:1.5, and since 1.5 is not a whole number, I concluded that the ratio must be 2:2:3, which helped me find my empirical formula. After doing this, I knew that I would have to compare the molar mass of the empirical formula to the molar mass of the actual substance (which was given in the problem), so I calculated the molar mass of the empirical formula and got approximately 74.0g. The molar mass of the actual substance was 90.0g, and I was very confused because when I compared these two masses, the ratio was 1:1.2. This didn't make any sense to me, because the molecuar formula would then have to be 1.2 times the empirical formula, which would be 2.4:2.4:3.6, which isn't right because the ratio would have to have whole numbers. I must have made an error somewhere throughout the course of this problem, and I hope that I will be able to find out what my error was. Other than that problem, I didn't have trouble on any of the others, so I think that the test went well for me overall.
        The day after the test, on Friday, we began our exploration of Unit 6 through the Black Box activity. Each student was given a box with a certain pattern inside, and we had to figure out what the pattern was without being able to see inside the box. I thought this task was very difficult; it was a challenge to rely on senses other than sight to be able to determine what was inside the box. The main idea of the activity was to get us thinking about the unknown and how we can determine the unknown without actually seeing it. This is significantly relative to atoms; scientists have been able to determine the structures of atoms though they are extremely tiny. This made me wonder how they were able to do this; how were scientists able to find out so much about something so small? This concept will be one of our main ideas throughout Unit 6, and I'm hoping that some of my questions will be answered throughout the course of the next couple weeks.