• Support PF! Buy your school textbooks, materials and every day products Here!

Number of atoms in CaSO4

  • Thread starter nando94
  • Start date
  • #1
33
0
I had a multiple choice problem on my pop quiz. How many oxygen atoms are there in .00334 grams of CaS04 X 2H2O.

The molar mass is 172 g/mol. So .00334/172 = 1.9 x 10-5 moles x 6 since there are 6 oxygen x 6.022 x 1023 = 7.016 x 1019.

None of the answer choices had that. Did I do it wrong? I'm gonna talk to my teacher about it tomorrow but its been bothering me lol.
 
Last edited:

Answers and Replies

  • #2
epenguin
Homework Helper
Gold Member
3,717
754
I had a multiple choice problem on my pop quiz. How many oxygen atoms are there in .00334 grams of CaS04 X 2H2O.

The is 172 g/mol. So .00334/172 = 1.9 x 10-5 moles x 6 since there are 6 oxygen x 6.022 x 1023 = 7.016 x 1019.

None of the answer choices had that. Did I do it wrong? I'm gonna talk to my teacher about it tomorrow but its been bothering me lol.
Some small arithmetical mistake? What is the nearest to yours among the answers? Yours seems to be close, I get 6.865 X 1019.

Oddly I get a slightly different molar, 175.5 mass from yours (miscounted H?) but anyway 1.9 X 10-5 moles. Your reasoning is correct so in that case, say it was an multiple choice exam you should go to the nearest to your number.
 
  • #3
33
0
I think the slightly different molar mass is due to differences between periodic tables.

The answer choices were 2, 6, 5.41 x 10^22, 5.81 x10^22, 1.11 x 10^21. Since your answer was very close to mine, I'm thinking that there was a typo on the quiz. If I saw your answer among the ones above I would have picked it but they weren't even close. Hopefully it is a typo haha and thanks for the help!
 
  • #4
Borek
Mentor
28,406
2,805
I got:

molar mass - 172.171 g/mol

moles - 1.940×10-5

oxygen atoms - 7.011×1019
 

Related Threads on Number of atoms in CaSO4

  • Last Post
Replies
6
Views
3K
Replies
1
Views
11K
  • Last Post
Replies
11
Views
2K
Replies
1
Views
1K
  • Last Post
Replies
1
Views
6K
Replies
0
Views
7K
Replies
0
Views
5K
Replies
1
Views
3K
  • Last Post
Replies
1
Views
2K
Top