Question

A household bleach solution contains 5.25% (by mass) NaClO. How many moles of NaClO are needed to make 1000 L of the solution? (density = 1.07g/mL)

This is the complete question on my assignment. It's 1000 L.

Answer 1

OK. The way I interpret this is that someone wants to make up 1,000 L of a solution that is 5.25% NaClO. If that's the right way I would do this. First I would change the mass percent to molarity or at least to moles/some volume.
5.25mass percent means
5.25 g NaClO/100 g solution. Since the density is 1.07, we can use the density to see what volume that is.
mass = v x d
m/d = v = 100g/1.07 = about 94 mL but you need to go through and do it more accurately.
Then you can determine number of moles in 5.25 g NaClO from moles = grams/molar mass. I get about 0.07 moles; again, you do it more accurately. So you actually have a solution that is about 0.07 moles/0.093 L. You want to make 1,000 L of that. I would simply multiply the ratio like this.'
0.07 moles x 1000L/0.093 L = moles NaClO required.

Actually, I think there is an easier way to do it. Why don't you do both and see if you get the same answer?
Density is 1.07 g/mL so 1000 mL has a mass of 1.07 g/mL x 1000 mL = 1070 grams. How much of that is NaClO. Its
1070 x 0.0525 = about 56 grams
How many moles is that?
56/74 = about 0.76 moles NaClO for 1 L of solution. To make 1000 L you multiply by 1000 to get about 760 moles.
I think the latter may be easier to understand.