Tuesday, January 25, 2011

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!

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