We can use our density of 1 gram per milliliter of water to

get into units of grams.

And then we can use the molar mass of water, 18.02 grams

per mole of water to find the moles of water.

And once we do the calculation which is 175 times 1,

divided by 18.02, we find that

we have 9.71 moles of water.

Now we can take the values we know, and plug in and find our mole fraction.

So we have the Greek symbol chi to represent mole fraction.

On the top I put our moles of solute, which is 0.427 moles.

And on the bottom I had to put both the moles of solute, the 0.427 moles,

plus the moles of the solvent, which we calculated and found to be 9.71 moles.

We don't multiply by the hundred, that's not the definition of mole fraction.

We can now find our mole fraction

of sodium chloride in this particular solution.

And so we get 0.0421 as our mole fraction.

Notice this is one of the few numbers that we write that do not

have a unit associated with them.

So our mole fraction of sodium chloride is 0.0421.

What i also know about mole fraction is that the mole fraction of sodium chloride

in this problem, plus the mole fraction of water, will equal to one.

So if I want to find the mole fraction of water,

I can do that as well by simply changing the value I put on top.

And what I should see is that the number I get for

the mole fraction of water, plus the mole fraction of sodium chloride,

should equal to one because that's the entire amount of sample.

The only two components are the solute and the solvent.