# Homework Help: How many Cr atoms in 78.82 g potassium dichromate?

1. Sep 26, 2006

### Banaticus

How many Cr atoms in 78.82 g potassium dichromate?
Potassium dichromate is $$\textrm{K}_{2}\textrm{Cr}_{2}\textrm{O}_{7}$$.

I said:

The molecular mass of potassium dichromate is:
39.1*2+52*2+16*7=294.2

So, in 78.82 g potassium dichromate, there are 78.82/294.2= 0.2680 moles of potassium dichromate. Each mole of potassium dichromate has $$6.022~x~10^{23}$$ molecules, each with 2 chromium atoms. So, in one mole, there are $$1.204~×~10^{24}$$ chromium atoms. So, in .2680 moles, there are $$.2680(1.2044~×~10^{24})~=~3.228~×~10^{23}$$, correct?

As a sidenote, it appears that LaTeX graphical formulas can't be seen in the preview mode -- the only way to check them is to post the message then edit the message if they're wrong? Also, where can I find a better LaTeX tutorial than https://www.physicsforums.com/misc/howtolatex.pdf which just doesn't give enough information? Ah, https://www.physicsforums.com/showthread.php?t=9021 has some pretty good information, but I still don't seem to be doing my LaTeX correctly.

Last edited by a moderator: Apr 22, 2017
2. Sep 26, 2006

### dmoravec

Yes, that looks good. And I don't currently know of any better LaTeX tutorial, I've just been learning it recently too and would also be interested in a more in depth tutorial.