% element by mass in soln.

  • Thread starter bxadook
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  • #1
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What is the percent CdSO4 by mass in a 1.0 molal aqueous solution?

My attempt:

CdSO4 is 208.47g/mol
1.0 molal = 1 mol CdSO4/1kgH2O
Converted mols to grams, and kg to g.
208.47g Cd/1000g H2O = .20847
.20847 x 100 to get % mass = 20.8%


It is an old test question that I am going over for finals week. I keep coming up with a different answer than what was on my test. I keep getting the value of 20.8%, which the answer listed on my test is 17.2%. Did my teacher make a failure in grading or did I just do something differently the first time around? I cant find my original work.
 

Answers and Replies

  • #2
symbolipoint
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You want the result as how? Percent weight per volume, or percent weight per weight? The rate might have been assumed to be straight weight or mass only:

208 grams Cadmium Sulfate in 208+1000 grams SOLUTION. This perspective will affect the percentage very much.
 
  • #3
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thank you i am retard
 
  • #4
symbolipoint
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thank you i am retard
No, not really; you just forgot which perspective to use. Your teacher did not specify, so you should probably pick percent weight. Really, the instructions in the practice test should specify either %w/w, or %w/v.
 
  • #5
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I think it is neither. It makes sense when you are calculating total % composition of Cadmium Sulphate that you would divide 208.47 by 1208.47 instead of just 1000. Because 1000g would just be the mass of the solvent not the soln.
 
  • #6
Borek
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17.5% w/w or 20.8% w/v, note that the second number can't be calculated without knowing solution density.
 

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