[r1509]

I am stuck on a question that seems fairly easy, but for some reason it is just not clicking with me.  I am supposed to calculate the number of moles of NaOCl in 4.0 mL of bleach, given that bleach is 6% NaOCl (w/w) and assuming it has the same density of water.

Initially, I set up the problem like this:

(4.0 mL NaOCl)x(1.0 g)x(1 mole NaOCl)  = 0.0538 moles NaOCl
                       (mL)            (74.4 g)

This is how I would calculate moles for water or any other liquid where the density was given.  However, this calculation does not include the given information of bleach being 6% NaOCl.  I am not sure how to use this information.  

Working backwards with the 6%, this is what I get:

.24 mL solute
-----------------  x 100 = 6%
4.0 mL solution

However, I am just not sure what the solute would be in this case, and how to use this information to calculate the number of moles.  I have the feeling I am getting way off track with this, so any help to steer me back in the right direction would be helpful.

[Mitch]

you solved for moles of water. moles of NaOCl would be 6% of the moles of water.

[r1509]

I'm not sure I understand what you mean.  How did I solve for moles of water?  We were supposed to assume the same density of water, but I did use the formula weight of NaOCl in the problem, which was 74.4 g/mole.

[Mitch]

Why don't you solve for grams of water first then. Then take 6% of that to determine grams of NaOCl

[r1509]

So is this right then?

(0.24 mL NaOCl)x(1.0 g)x(1 mole NaOCl) = 0.00323 moles NaOCl
                           (mL)        (74.4 g)

I used the 0.24 mL NaOCl since that is 6% of the total (4.0 mL).  So I am thinking this should give me the correct number of moles of NaOCl.

[Mitch]

seems okay