Wednesday, October 13, 2010

To begin class we opened up our unit 2 packets to page 14. Here Mr. Henderson reviewed how a mass spectrometer is a device that measures the average atomic mass of different isotopes of an element. We then reviewed how to do problems one and two which were problems finding the average atomic mass of elements.

We then pretended that number three of page 14 was a test question. After we finished this Mr. Henderson started to talk about the test. To begin he put a slight twist the problem number three. Instead of having both percentages of abundance and atomic mass units for both isotopes, you might only have one percentage of abundance and atomic mass units, but you will also have a periodic table.

For example, if number three of page 14 said, "Determine the atomic mass and abundance of isotope 65 copper if isotope 63 copper occurs naturally as 69.09%."

To find the abundance: 100% (in nature)-69.09% (isotope 63)

This would equal to 30.91% (isotope 65).

To find the atomic mass unit: first find copper's atomic mass on the periodic table (63.55 amu)

Now you can set up an equation relating these terms

63.55 (average atomic mass unit)=.6909(abundance-isotope 63) x 62.93(relative mass) + .3091(abundance-isotope 65)X(relative mass)

Simplify: 63.55 = 43.48 + .3091X

20.07 = .3091X

64.93 = X

Isotope 65 Copper has a relative atomic mass unit of 64.93.

If you need help with this concept please visit: http://www.algebralab.com/practice/practice.aspx?file=Algebra_AverageAtomicMass.xml

Also on the test, there will be 35 multiple choice questions. We will have to know the history of atoms and what scientists contributed, isotope notation, the periodic table (periods, groups, and families), cations and anions, and naming of compounds. Furthermore, there will be one page (write and show work section) that you will need to know how to convert formulas into names and names into formulas. In this section there will be a problem similar to the example I described above.

We continued class by going over yesterday's blog and started unit 3. We immediately started conversion-factor problems on page one. Mr. Henderson taught us how to convert decades into seconds or even puggets into illies. You can do this by using easy information that you already know either common knowledge or the knowledge they give you in the problem.

For example, if I wanted to find out how many seconds are in a day, I would use this conversion-factor method. I know that there are 24 hours in 2 days. I also know that there are 60 minutes in 1 hour and 60 seconds in 1 minute. So, I would set up my expression like this:

2 days* 24 hrs 60 minutes 60 seconds

1 day * 1 hour *1 minute

I then would cancel out the same units because I know that units that are "upstairs" cancel out with the same units "downstairs."

So, my new equation would be:

2 *24*60*60 seconds

1

So, there are 172,800 seconds in 2 days.

After working busily on page one, the bell rang and class was over. We accomplished a lot on a day when we had shortened classes.