Question

How many grams of NaCl (molar mass = 58.4 g/mole) must be added to 12.0 g of water (molar mass = 18.0 g/mole) so that Xwater = 0.725?

My answer was 102.69 grams of NaCl. However my friend got 14.8 grams of NaCL. We are not sure who is right? Please respond, and thank you.

I get 14.77 which rounds to 14.8 g NaCl. I can find your error if you want to post your work.

12g x (1mole/18g)= .667 moles H20
.725=(x)/(x + .667)
.725x + .484=x (subtract .725)
.484=.275x
.484/.275=x
1.76=x
1.76moles x (58.4g/1mole)= 102.78g NaCl

Not sure what I'm doing wrong... :(


12g x (1mole/18g)= .667 moles H20 <b>ok</b>
.725=(x)/(x + .667)<b>The error is here. You should have </b><i>
[mols H2O/(mols H2O + mols NaCl)]=0.725. So it should be [0.667/(0.667 + x)]=0.725. </i>
.725x + .484=x (subtract .725)
.484=.275x
.484/.275=x
1.76=x
1.76moles x (58.4g/1mole)= 102.78g NaCl

Not sure what I'm doing wrong... :(
<b>I hope this helps.</b>