[willor]

Hi everyone, before I get into my question just want to say what a great resource this site is, has helped me in so many ways with my study of chemistry, so thank you all for taking the time to answer questions here.

About my problem: I have a question involving molarity, the question is "A concentrated solution of perchloric acid, HClO4, is 11.7 M and has a density of 1.67 g/mL. What is the mass percent perchloric acid in this solution?"

The way I solved it was to say that the percent composition = X g HClO4/100 g HClO4 = 11.7 mol HClO4 / 1.00 L Soln X (1000mL soln/1 L soln) X (1.67g soln/1 mL soln) X (1 mol HClO4/ 100.46g HClO4) = 70.4% HClO4 by mass.

So I got the correct answer by treating it like an algebra equation where I'd normally be solving for the molarity of the solution and just rearranged it to equal the percent composition.

My question is if there is a more efficient way to solve this problem? I ask because I wasn't really sure of the basis behind my method of solving it other then it makes sense from an algebraic perspective to me. Any help here would be greatly appreciated. Thanks alot.

[Borek]

Final answer is OK, although I don't get this one:

percent composition = X g HClO4/100 g HClO4

Should be per 100g of solution, not pure acid.

As for the more efficient way - I am not aware of one. See percentage to molarity conversion example.To speed up calculations you may use concentration cheat sheet.

[Donaldson Tan]

The concentration cheat sheet can be printed on any good b&w printer - I have tested it on almost 10 years old LaserJet 5L and the results were perfect.

LOL..

[Borek]

The concentration cheat sheet can be printed on any good b&w printer - I have tested it on almost 10 years old LaserJet 5L and the results were perfect.

LOL..

What's so funny? Fact that I am not seeing the reason to buy a new printer as long as the old one works OK?