Posted by Helpplease on .
A perchloric acid solution is composed of 168.75 g of perchloric acid and 81.25 mL of pure water. What is the percent by mass of the perchloric acid solution? The density of
water is 1.000 g/mL.
When I did this part I got 67.5%
But, I am having trouble with the secind part.
The density of the above perchloric acid solution is 1.138 g/mL. What is the molarity of the perchloric acid solution?
I know molarity is moles solute/liter of solution, but how do i find that from %mass? please help if you can!! Thanks!

Science, not "12th grade" 
Writeacher,
Please type your subject in the School Subject box. Any other words, including obscure abbreviations, are likely to delay responses from a teacher who knows that subject well.

12th grade 
Help,
Okay, sorry....I posted it again correctly :)

12th grade chemistry 
drwls,
Use the combined mass (250 g) and the density of the solution (which you were given) to compute the volume of the solution. Once you have the mass of perchloric acid and the total volume, molarity is easily computed.
The formula for percholroic acid is HClO4. You will need that for the molecular weight, if you are computing the molarity of the solution.