Re: how many protons there are in 5.0x10 to the 3power grams of xenon

Well - 

I  could just give you a number, but you are clearly a smart student and 
that is the LAST thing you want.  So I will give you the tools to work  
through the probobly 7 jillion similar problems you are likely to face 
between here and the end of the class.

And yes, I will work you through a similar problem, and give you the answer,  
then set you up to answer you problem.

my problem:  How many neutrons in 7.0x10^2g Fr (hint: "^" means "to the 
power of")

First - waht do we need to know to answer this silly problem.

1)How many Fr in that many grams?
2)How many neutrons in a Fr?

--------------side note-----------------
I am not sure what you mean in this context by % abundance - but I am 
guessing it means what % of the entire mass is the thing they were asking 
about (in my question neutrons - and in your question protons).  If this is 
the case, simply find the mass of your protons,  and divide by the original 
number of grams.

IF on the other hand you mean the abundance of different isotopes - for a 
proton question IT DOESN'T MATTER.  Abundance only matters when looking or 
NEUTRONS.  All xenons MUST have 54 protons or they are something else.  For 
neutron questions you kind of need the abundance of different isotopes.  But 
I was going to do it by looking at the molecular mass.
--------------side note-----------------------------

so 1) 7.0x10^2 g Fr x (1mol Fr/223 g Fr) = 156100 mol Fr 
    
	156100 mol Fr x (6.02x10^23 Fr/1mol Fr) = 9.3972 x10^28 atoms Fr
(worry about sig figs at the very end)

and 2) 1 Fr is 223 m.w. (molecular weight) and since its atomic number is 87 
it has 87 protons. So 223 - 87 = 136 neutrons.  223 is the average m.w. so 
136 is the average number of neutrons.  It would be a more complex problem 
if you had to juggle abundances... but not too bad.

Now you know 136 neutrons/atom Fr, and 9.3972x10^28 atoms Fr
just multiply (look at the units!!!)

136 neutrons/atom Fr x 9.3972x10^28 atoms Fr =1.3x10^31 neutrons

-------------

So now for your problem:

1) how many atoms of Xe:
	g Xe x (1mol Xe/131 gXe) x (6.02x10^23 atoms Xe/ 1mol Xe) = 

2) how many protons in an Xe: look at your periodic table!

and then multiply!

In general - figure out what you need to solve the problem.  Also look at 
the units of the numbers you are given in the problem, the units of your 
answer... and what transformations you need to do to get one from the other.  
The students who learn this method are often able to figure out problems 
they have never seen before.

Good luck!

Greta Hardin