How to convert from w/w% to molarity?
Weight percent is essentially the same as (I arbitrarily picked grams as the mass unit):

$$
\%~\mathrm{w/w~X} = \mathrm{g~X\over g~solution}
$$

In order to get to the $\mathrm{mol\over L}$ units of molarity, you have to convert by multiplying by the solution density, $\rho$, and dividing by the molecular weight of $\mathrm X$, $M_\mathrm{X}$:

$$
\mathrm{g~X\over g~solution} \times \stackrel{\left(1\over M_\mathrm X\right)}{\mathrm{mol~X\over g~X}} 
 \times \stackrel{\left(\rho\right)}{\mathrm{g~solution\over L~solution}}
 = \mathrm{mol~X\over L~solution}
$$

One key thing to remember is that $\rho$ is the density of the solution, not of the pure solvent. If you're working with dilute solutions (below $\sim\!100~\mathrm{mM}$ for aqueous) these two densities will be similar, but in concentrated solutions they will diverge.