Chemistry help! (Atomic Mass)

Weasel2013 · Nov 3, 2010

Closed, Kero rocks my socks.

Koot · Nov 3, 2010

Weasel2013 said: ↑

Without doing any math, are there more chlorine-35 atoms or more chlorine-37 atoms on Earth?

35 atoms because the general weight is 35.45 so there must be more 35 atoms to bring the average weight closer to 35.

What is the atomic mass of hafnium if out of every 200 atoms, 10 have mass 176.00 amu, 38 have mass 177.00 amu, 54 have mass 178.00 amu, 28 have mass 179.00 amu, and 70 have mass 180.00 amu?
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In a sample of 200 chlorine atoms, it is found that 151 are 35Cl (34.969 amu), and 49 are37Cl (36.966 amu). What is the average atomic mass of chlorine?

I'm not going to do the math but the way to solve these two problems is to multiply the weight of the isotopes by the percentage that they occur. Do this for all the isotopes and add up the resulting numbers. This should be the average.
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Copper used in electric wires comes in two types: copper-63 and copper-65. Copper-63 has an atomic mass of 62.9298 amu and an abundance of 69.09%. The other isotope, copper-65, has an abundance of 30.91%. The average atomic mass between these two isotopes is 63.546 amu. Calculate the actual atomic mass of copper-65.

Same as above, but you'll be working backwards kind of.
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Magnesium consists of three naturally occurring isotopes. The percent abundance of these isotopes is as follows: 24Mg (78.70%), 25Mg (10.13%), and 26Mg (11.7%). The average atomic mass of the three isotopes is 24.3050 amu. If the atomic mass of 25Mg is 24.98584 amu, and 26Mg is 25.98259 amu, calculate the actual atomic mass of 24Mg.
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Naturally occurring chlorine that is put in pools is 75.53 percent chlorine-35 (mass = 34.969 amu) and 24.47 percent chlorine-37 (mass = 36.966 amu). Calculate the average atomic mass.
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Why is the mass in amu of a carbon-12 atom reported as 12.011 in the periodic table of the elements?
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Using the info I wrote for problem 2 you should be able to solve all these problems. I'm not going to do the work for you as you'll learn nothing, I just told you how and why. Post back if you have any questions.

Weasel2013 · Nov 3, 2010

I would really like the answers to verify my own work...

KerokeroCola · Nov 3, 2010

1. Cl-35

2. 178.55 AMU

3. 35.46 AMU

4. 65.11 AMU

5. 23.8 AMU

6. 35.56 AMU

7. The mass of carbon-12 on the periodic table is higher than 12.000 (exactly 12.000 because C-12 is the standard for AMU) because this is an average mass of all of carbon's isotopes. Since Carbon exists as C-12 and C-14 (mass of about 14), its "average mass" is slightly higher than 12.

You better have actually done your own work...