[FouRRaW]

A 1.35 M NaCl solution has a density of 1.054g/mL at 20 degrees celcius.
How many grams of solvent are present in 650 mL of this solution.

I get a different answer than my teacher, here's what i did...

1. figure out the total mass of solution --> 1.054 g/mL x 650 mL = 685.1g
2. calculate moles NaCl = (Molarity) x (total volume) --> 1.35M x 0.650 L  = 0.8775 mol
3. Mass NaCl  = moles x mm --> mass NaCl =(0.8775mol) x (58.44g/mol) = 31.107g
4. Calculate mass solvent by subtracting total mass solution-mass solute(NaCl) --> Mass Solute = 685.1 g - 31.107 g = 653.99g

That was my answer, my teacher however got --> mass solvent = 685 - 51.3 g = 633.7g    ( as his final step )

Any help would be awesome, thanks.

[Ψ×Ψ]

You did everything right, except for a calculator screw-up.

3. Mass NaCl  = moles x mm --> mass NaCl =(0.8775mol) x (58.44g/mol) = 31.107g

.8775 x 58.44 = 51.28

Happens to the best of us. 

[enahs]

Darn, she beat me to it. I even got the red warning post!
The number you multiplied it by also happens to be ~ MW of Cl, so it looks like when you typed it in your calculator you might have forgot to just add the Na in there.

[FouRRaW]

Perfect, so i at least i know i understand the concepts

Thanks a lot, both of you.