Week 5 Blog

Ariana Trossen
Dr. Finnan
SG Chem 2
10/17/15

     This week in chemistry we did a lot of practice to prepare us for our test which we had at the end of the week on Friday. Our test covered Unit 5 which is all about counting particles. Last week we mastered the basics and were introduced to some more complicated concepts of counting particles. This week we mastered the more complicated concepts and showed our understanding on our tests.
Some of the more complicated concepts include calculating how many moles, molecules, or atoms are in an element or compound, empirical formulas, and molecular formulas. At the beginning of the week I felt a little unsure about these concepts, but now I feel a lot more confident about them.

     To begin the week we took a look at the packet from last week that asked about the number of atoms, molecules, or moles in an element or compound. Each group was assigned a different problem from the packet to whiteboard. Our group was assigned problem #7, which asked us to find the number of atoms in Bottle 7. Bottle 7 contained some iron nails. In order to solve the problem, we have to start by finding the mass of the bottle with the nails inside, then we have to subtract the Tare Weight (T.W.) from that mass. The T.W. is the mass of the bottle when it is empty. By subtracting the T.W. from the mass of the bottle with the nails we find the mass of the iron nails by themselves. After that you have to find what 1 mole of iron is by looking at the periodic table. Then you divide the mass of the iron nails by that number. This will equal how many moles of iron the iron nails are. With this new number you multiply it by Avogadro's number, which is 6.022×10²³, and you will find the number of atoms in the iron nails contained in Bottle 7.

     After more practice with problems solving for the number of atoms, molecules, and moles in elements and compounds, we began to look at empirical and molecular formulas more. The difference between empirical and molecular formulas is empirical formulas are based on data and molecular formulas are what the compound's formula truly is. Molecular formulas are generally more complicated, and empirical formulas are more simple. To find the empirical formula of a compound you have to start by finding the number of moles of each element in the compound. Then, you find the ratio of the moles to find out how many atoms of each elements are in a molecule of that compound. This will tell you what the empirical formula is. To find the molecular formula you start the same way as you do to find the empirical formula, but then you go on by taking the given mass of the compound and dividing it by the sum of the atomic masses of the elements in the compound. This will give you a number which you will multiply by the number of atoms you found for each element in the empirical formula. By multiplying, you find the more complicated molecular formula of the compound.

     Before the test we were given a review guide to cover everything we went over in Unit 5. From the definition of a mole to finding the percentages of elements that make up a compound, we reviewed for the test. Then on Friday we took it. I was a little nervous coming in, but as we started and I began to answer the questions with confidence, I wasn't nervous anymore. I feel that I have a very good understanding of the concepts in Unit 5, Counting Particles.