chemistry........help!! =)
posted by Lisa, Help needed! on .
One brand of laundry bleach is an aqueous solution containing 4.00% sodium hypochlorite (NaOCl) by mass
What is the molarity of this solution? (Assume a density of 1.02 g/mL .)

The question tells us that the concentration of the solution is 4.00% w/w.
That is 100 g of the solution contains 4.00 g NaOCl.
or
That is 1000 g of the solution contains 40.0 g NaOCl
The volume occupied by 1000 g is
mass/density
1000g/1.02 g ml^1 = 980.4 ml
Molar mass of NaOCl is 74.44 g/mol
Number of moles of NaOCl is
40.0 g/74.44 g/mol = 0.5373 mole
so molarity is
moles/volume = 
.54804