Week 3 Blog

Ariana Trossen
Dr. Finnan
SG Chem 2
3/10/15

     This week we took our Unit 4 test and started Unit 5. On Monday and Tuesday we spent time reviewing and preparing for the test. We started class on Monday by white boarding out the answers to the last two problems from Unit 4 Worksheet 4. Our group was assigned problem 6. By comparing the ratio of masses in two compounds, we can determine the formula for the  second compound based on the first. In this case we knew that compound 1 was water, with the formula H2O, and had a mass ratio of 1/8 (hydrogen/oxygen). The mass ratio of compound 2 was 1/16, from this we found that its formula would be H2O2, hydrogen peroxide. This is because we know the number of hydrogen in each formula stays the same based on the formula for water having two hydrogens and the numerators in each mas ratio, which represents hydrogen in each compound, are the same. The number of oxygens in compound 2 is twice the amount in compound 1 because the denominator, which represents oxygen in each compound, in compound 2 is twice that in compound one. We were able to determine the formula for one compound based on the mass ratios for each and knowing what one of the compounds was.

     On Tuesday we worked on the Unit 4 Review packet. We went back to the beginning of this unit and worked our way to the end testing our knowledge, before the actual test. First, we studied the differences between elements, compounds, mixtures, and pure substances. Elements cannot be broken down by chemical or physical means. Mixtures are variable; their physical properties depend on the composition, and can be separated by physical means. Compounds can only be separated by chemical means, and consist of two or more elements in a fixed mass ratio. We then identified different compounds, mixtures, and elements as particle drawings. 

    We continued our review by sketching out how different gases react to form compounds. An important thing we learned was about diatomic atoms. Hydrogen, oxygen, fluorine, chlorine, bromine, iodine, and astatine are all diatomic. This means that they don't occur as single atoms, but two of the same element bonded together.

      We reviewed further with mass ratio comparisons of different compounds, similar to problem 6 on Unit 4 Worksheet 4. With the ratios we were able to sketch particle diagrams of the two different compounds, and then write out formulas for each.

     Different elements have different properties, such as melting and boiling points. We showed this by using time and temperature graphs lines showing the relationships between different elements and their boiling points. If you were to have a mixture of two different elements, you could heat the mixture to the temperature of the lowest boiling point of the two elements and separate them in this way.

     On Wednesday we took the Unit 4 test, which covered all of these concepts. Then we went  on to start Unit 5, Counting Particles.

     To begin to understand the concept of counting particles, we looked at relative mass of different kinds of hardware. We discovered that by weighing things you can count them, by knowing the mass of something you can determine how many of that something there is.

     To end the week we began to dive into comparing the relative masses of different elements in various oxides. By this we were able to see how Dalton's assumption of relative mass compares to the adjusted relative mass. Since we did not have enough time to finish this worksheet in class, I am still a little confused on how they compare. Altogether, this week I feel very good about my knowledge on Unit 4 after scoring a 33/34, and am excited to continue learning how to count particles in Unit 5.