I've been studying a bit of chemistry over the past month and this question just so happened to be one that it looked like I might be able to understand, so I figured I would try solving it using the methods I've learned so far. Here goes:
1.) 518g of Spodumene (LiAlSi2
Breaks down to:
- 310.8g of O (518g / 10 = 51.8g - - considering 6 parts oxygen, we have 51.8*6 = 310.8g)
- 103.6g of Si (number obtained in a manner analogous to the above example)
- 51.8g of Li (as above)
- 51.8g of Al (as above)
2.)Using an atomic weight of 6.94 for Li, we then have 7.46 moles of Li (51.8g / 6.94)
3.)To obtain the number of atoms present in the 7.46 moles of Li we take 7.46 * 6.02x1023
which comes out to 4.49x1024
which is the number of atoms of Li present in our 518g sample of Spodumene.
4.)Considering the question specifically asked for the number of Li-6
atoms, I believe (per Borek's informative post) that we would take 7.3% of this above number. So, 4.49x1024
* .073 = 3.2777x1023
, which should be the number of Li-6 atoms in the sample?
I'm reasonably certain I did okay up until step 4. I don't really understand how to isolate the number of a certain isotope of an element as is requested in the problem, but using Borek's post I took a whack at it.