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Hey all, I'm working some of the problems out of the Kaplan OAT booklet and I'm confused on a question. (It's #28 on the first practice set of the natural sciences section.)
The question asks how many grams of Al2(SO4)3 are needed to make 87.5 grams of 0.3 m Al2(SO4)3 solution.
I calculated the molecular weight and it came out to be 98 grams. I multiplied 98 g/mol x 0.3 mol/Kg solvent = 102.6 g/Kg solvent, to find out how many grams of Al2(SO4)3 per Kg solvent. I set up a ratio by multiplying the (87.5 g x 102.6g) / 1000 g to get my answer.
In the solution, it says that I have to add 102.6 g to 1000 g in order to find out the total mass of the solution. I thought that molality = moles/ Kg of SOLVENT and not the solution. Is there something that I'm not getting here?
The question asks how many grams of Al2(SO4)3 are needed to make 87.5 grams of 0.3 m Al2(SO4)3 solution.
I calculated the molecular weight and it came out to be 98 grams. I multiplied 98 g/mol x 0.3 mol/Kg solvent = 102.6 g/Kg solvent, to find out how many grams of Al2(SO4)3 per Kg solvent. I set up a ratio by multiplying the (87.5 g x 102.6g) / 1000 g to get my answer.
In the solution, it says that I have to add 102.6 g to 1000 g in order to find out the total mass of the solution. I thought that molality = moles/ Kg of SOLVENT and not the solution. Is there something that I'm not getting here?