[ajax0604]

Here is the question:
10mL sample of Fluorosulfuric acid, HSO3F, has a molarity of 9.3M.
Express the concentration as percentage by mass.
There is no information about what the mass of the 10mL sample is or its density.

The teacher said to solve it this way:
9.3M = 9.3mol/L
convert the numer of moles into grams, so 9.3mol/L = 930.93g/L
Then assume the mass of solution is 1000g since there is 1 litre.
Is this really an accurate assumption? I've looked up the density of HSO3F and it's significantly higher than water at 1.84g/cm3 so wouldn't a litre of this solution have a mass a lot higher than 1000g?

[Dan]

I've looked up the density of HSO3F and it's significantly higher than water at 1.84g/cm3 so wouldn't a litre of this solution have a mass a lot higher than 1000g?

Yes, you are right. You need to know the density of the solution, and assuming it to be 1 g/L is a poor assumption because the concentration is very high. If the starting concentration was much lower, say 0.1 M, then estimating density at 1 g/L would be acceptable (assuming the solvent is water).