## Fundamentals E9

Tim Foster 2A
Posts: 73
Joined: Fri Sep 29, 2017 7:07 am

### Fundamentals E9

The question asks how many atoms of oxygen are in 5.15 grams of epsom salt, or magnesium sulfate heptahydrate. Firstly, are we going to need to know nomenclature like this for the midterm? Secondly, I googled the formula and got MgSO4(7H20). I am unsure of whether or not this problem would like me to include the heptahydrate in my calculations, but with or without it I get the %mass composition of oxygen to be about 53%. I keep getting the number of atoms to be 1.03x10^23, but the book says it is 1.38x10^23. Could someone work through this problem with me? Thanks!

Isabella Sanzi 2E
Posts: 54
Joined: Thu Jul 13, 2017 3:00 am

### Re: Fundamentals E9

To answer your first question, I do not think we will need to know nomenclature like this on the midterm as we have not gone over it in class at all, nor has it been in the readings.
Second, yes, you would include the hydrate in your calculations as it is part of the compound for which you are trying to find the number of atoms.
And to answer your third question, here is how I worked through the problem to get the correct answer:
First I found that the molar mass was 246.48 g/mol and found the number of moles of the 5.15 grams of magnesium sulfate heptahydrate. Next I multiplied that by the number of moles of oxygen in the compound (which in this case is 11, 7 moles coming from the hydrate and 4 coming from the sulfate). then I multiplied the result of that by Avogadro's Number (6.0221 x 10^23) to find the final answer found in the book.
I hope this helps!