Let's say that I want to convert concentration of an acid from % to molarity. One way I found to do this is by using the following formula: percentage = (molarity * molar mass) / 10.
Another way is to use an equivalency chart like this one (see bottom of page): http://www.ochemonline.com/Acid_and_Base_Concentrations
For example, to convert 38% HCl to molarity I calculated: 38% = (molarity * 36.46) / 10 and molarity = 10.42 = 10 M. However, the equivalency chart says that 38% is actually 12.4 M.
The same discrepancy happened when I tried to convert 68% nitric acid molarity. Using the equation, I got molarity to equal 11 M, however, according to another source 68% nitric acid is closer to 15 M.
So my questions are:
1) Is there something I'm doing wrong that I get such a huge discrepancy?
2) What's the best way to figure out molarity from % and vice versa?