GC help

[hope_to_match]

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I need help with a few question in GC...

1) What is the percentage of Oxygen by mass in a 200 gram sample of CuSO4 5H2O

I understand that 200 g is an extraneous information. This is how I solved the problem:

1) I found the overall molas mass of the sample by adding the weights and multiplying by coefficients whenever required (i.e. for oxygen and hydrogen)= (approximately) 250

2)Then I found out the mass of Oxygen: 4(16) + 5(16)

3) Divide mass of oxygen by overall mass from step 1

My question is: why the heck does KBB in step 2 multiply 4(16) x 5(16) instead of adding like I did? Am I missing something? Can someone please explain this to me? Thanks..

 

[LazyP]

I believe its an error...it should be "+" so you are right!