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# Chemistry (including Biochemistry)/Finding the number of atoms

Question
Dear Dr. Boyter,

5.00g of copper(II) sulfate pentahydrate (CuSO4·5H2O) contains how many atoms of oxygen?

- So first I will show my work that I have done so far up until the point where I got stuck. (By the way, I am in Grade 10, Advanced Science Course, and I am using dimensional analysis for this question).

- I know that there are 5 grams of CuSO4·5H2O
- There are 5 oxygen atoms in 1 mol CuSO4·5H2O (I think)
- Using my textbook, I calculated the molar mass of CuSO4·5H2O to be
185.72g
- There are 6.02*10^23 molecules of CuSO4·5H2O in 1 mol of CuSO4·5H2O

5.00g CuSO4·5H2O * 1mol CuSO4·5H2O/185.72g CuSO4·5H2O = 0.02692224854mol

0.02692224854mol * (6.02)(10^23) molecules CuSO4·5H2O/1mol CuSO4·5H2O = 1.62*10^22 molecules

- Now I have gotten to the point where I am unsure of what to do next. Convert units? Multiply? Or divide? And by which terms? What do I need to do in order to find how many "oxygen atoms" are in 5 grams of CuSO4·5H2O? Thanks in advance for your time and help is much appreciated.

First, thanks giving giving your school info and showing what you tried. Very few do that and it is appreciated. Good job.

"There are 5 oxygen atoms in 1 mol CuSO4·5H2O (I think)"

Actually there are 9, 5 from the water and 4 from the sulfate (SO4)

Second, it is not atoms per mol, either

There are 9 oxygen atoms in 1 molecule of CuSO4·5H2O or
There are 9 oxygen mols in 1 mol of CuSO4·5H2O

Your math setup is correct, just one step short

5.00g CuSO4·5H2O * 1mol CuSO4·5H2O/185.72g CuSO4·5H2O = 0.02692224854mol

0.02692224854mol * (6.02)(10^23) molecules CuSO4·5H2O/1mol CuSO4·5H2O = 1.62*10^22 molecules

1.62*10^22 molecules CuSO4·5H2O * 9 oxygen atoms / 1 molecule of CuSO4·5H2O = atoms oxygen

I'll let you do the math of that last step. Also, I assume the molecular weight is correct.

Write back if it isn't clear.
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Chemistry (including Biochemistry)

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#### Dr. Henry Boyter, Jr.

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No homework, biochemistry, or other schoolwork! The question will be rejected. If you have not searched www.google.com, do so before posting. If you are a student, give your grade and course. Everyone, explain the purpose and context for the question.
Experience in the area
Chemistry (non-biochemistry), environmental science, occupational health and safety, environmental regulation and management, environmental engineering, and wastewater engineering. I'm the Director of Environmental, Health, and Safety and the Director of Research at the Institute of Textile Technology.

##### Experience

Chemistry (non-biochemistry), environmental science, occupational health and safety, environmental regulation and management, environmental engineering, and wastewater engineering. I'm the Director of Environmental, Health, and Safety and the Director of Research at the Institute of Textile Technology.

Education/Credentials
PhD, MS, BS in Chemistry