Carminic acid is a naturally occuring red pigment and contains only carbon, hydrogen, and oxygen. It is 53.66% C and 4.0p% H by mass. A titration required 18.02 mL of 0.0406 M NaOH to neutralize 0.3602 g of carminic acid. Assuming that there is only one acidic hydrogen per molecule, what is the molecular formula of carminic acid?

Answer 1

Take a 100 gram sample.
That gives you
53.66 g C =
4.0p (or whatever that p is supposed to be) grams.
100-4.0p-53.66 = g oxygen.

Now convert to moles.'
53.66/molar mass C
4.0p/1 = moles H
g oxygen/16 = mols O

Now find the ratio of these three elements to each other, in small whole numbers, with the lowest number being no less than 1.00. The easy way to do that is to divide the smallest number by itself (thus 1.000 for that element), then divide the other two numbers by the same small number. Round to whole numbers but don't round too much; i.e., no more than about 0.1 or so.
Post your work if you get stuck. I've looked at the numbers and they don't look that good. Check to make sure you didn't make a typo in the numbers.