What is the percent composition of CdSO4 in a 1.0 molal aqueous solution?

[bxadook]

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 can't find my original work.

 

[symbolipoint]

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.

 

[bxadook]

thank you i am retard

 

[symbolipoint]

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.

 

[bxadook]

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.

 

[Borek]

17.5% w/w or 20.8% w/v, note that the second number can't be calculated without knowing solution density.