Moles and Molar Mass

Today in chemistry, we picked up additional worksheets that went along with Unit 8. We then worked on pages 7 and 8 to refresh our minds on ionic and covalent formulas. Remember that an ionic compound consists of a metal and a non-metal. Covalent compounds consists of only non-metals. Writing the name of the formula depends on what compound it is. On page 8 of the review, we started to determine the molecular mass of compounds. When given a compound, you must write out the formula first. Then, count how many atoms are in the first element and multiply that number by the element's atomic mass. The atomic mass can be found on the periodic table. Do the same thing with the second element in the formula. Then, add these two products together and the sum you get is the molar mass. An example would be like this:

Compound given: carbon dioxide
Formula: CO2
There is one C so you multiply 1 by the atomic mass. Carbon's atomic mass is 12.01 grams. 1 x 12.01 g. Looking at oxygen, it has two atoms. The atomic mass of Oxygen is 16.00 grams. 2 x 16.00 g. Then you add these two products. The answer is 44.01. The equation should look like this: (1 x 12.01 g) + (2 x 16.00 g) = 44.01 grams.


The next thing we did was how to calculate the number of moles. You had to apply your knowledge of molar mass to figure out how to do this. It is like unit conversion. An example would be like this: 50 g of carbon dioxide.
You should write down the number that is given to you so you should write out 50 g of CO2. You need to multiply this by something. Since we want to figure out the number of moles in a compound, we would write 1 mole of CO2 at the top of the dividing line. At the bottom would be the molar mass of CO2 and the unit should be g of CO2 since we want to cancel this out. You then calculate all this and the answer should come out to be 1.14 moles of CO2. The equation should look like this:
50 g of CO2 x 1 mole of CO2/44.01 g of CO2 = 1.14 moles of CO2.

After completing pages 7 and 8, we started on page 1. It pretty much had the same concept on what we did on page 8. Near the end of class, Mrs. Mandarino stamped the labs.
Homework is to complete worksheets pg 1 and 2!

January 7, 2011

In Mrs. M class, Friday we did the usual getting the homework stamped and looked over it. Following it we got off track talking about other things. In doing so we made it impossible to go over all of the neccessary information on the test. But we did go over half lives a bit more along with chain reactions and nucleor reactors. If you forgot, half-lives are the length of time it takes for a substance to decay over a period of time. Every set of years half of the substance dissapears until stable or gone. Chain reactions occur during Fission not fusion. Fission is the splitting of atoms and fusion is the combining of them. Fission occurs when a neutron hits a bigger nucleus causing large amounts of energy to be released in different elements and more nuetrons. More can be found on page 15 of the worksheets. Nuclear Reactors are divided into three parts. A.) Control rods absorb neutrons to slow down chain reactions B)Fuel Rods contain 3 percent of U-235 C.) Moderator slows down neutrons so they can be absorbed by the control rods. Again since we talked during class we ran out of time and did not cover Ionizing Radiation or Radon and we do not have to learn it for the test. Remember the test is MONDAY!
Happy Studies.
M.J.

January 4, 2011

Today in chemistry, Mrs. M asked for us to bring our journals to get them stamped for the homework of the previous night which was page 3. After stamping we went over page 3 and checked all of our answers. Then we moved onto page 6 and learned about isotopes. Isotopes are atoms that have the same number of protons but have a different number of neutrons. Then we started pages 5 and 7 for practice to get familiar with how to identify: the isotope symbol, the name of the isotope, the atomic number, the mass number, number of electrons (in a neutral atom), the number of protons, and the number of neutrons.

• To find the isotope symbol you have to put the mass number on top of number of protons the element has, then put the element's symbol after that.

After finishing with page 7 we moved onto page 10 and learned about "half-lives." A half-life is the period of time it takes for a substance undergoing decay to decrease by half. We then practiced using half-lives to figure out a problem. Then class ended and Mrs. M assigned us page 9 and page 10 #3 for homework.

P.S. HAPPY NEW YEAR ;)

- Taso K.