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Chemistry (including Biochemistry)/Finding the number of atoms

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Question
Dear Dr. Boyter,

5.00g of copper(II) sulfate pentahydrate (CuSO45H2O) 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 CuSO45H2O
  - There are 5 oxygen atoms in 1 mol CuSO45H2O (I think)
  - Using my textbook, I calculated the molar mass of CuSO45H2O to be
    185.72g          
  - There are 6.02*10^23 molecules of CuSO45H2O in 1 mol of CuSO45H2O

5.00g CuSO45H2O * 1mol CuSO45H2O/185.72g CuSO45H2O = 0.02692224854mol

0.02692224854mol * (6.02)(10^23) molecules CuSO45H2O/1mol CuSO45H2O = 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 CuSO45H2O? Thanks in advance for your time and help is much appreciated.

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

Your first error

"There are 5 oxygen atoms in 1 mol CuSO45H2O (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 CuSO45H2O or
There are 9 oxygen mols in 1 mol of CuSO45H2O

Your math setup is correct, just one step short

5.00g CuSO45H2O * 1mol CuSO45H2O/185.72g CuSO45H2O = 0.02692224854mol

0.02692224854mol * (6.02)(10^23) molecules CuSO45H2O/1mol CuSO45H2O = 1.62*10^22 molecules

1.62*10^22 molecules CuSO45H2O * 9 oxygen atoms / 1 molecule of CuSO45H2O = 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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Dr. Henry Boyter, Jr.

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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

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