Posted by Chem is try on Sunday, October 3, 2010 at 10:37am.
8.3 grams of NaCl and 3 grams of KBr were dissolved in 47 mL of water. What is the mole fraction of KBr in the solution?
I know that the mole fraction of the KBr and Nacl (without using the mL H2O is .2, but, i am confused on where i use that mL in the problem.) Please help!
- AP chemistry - bobpursley, Sunday, October 3, 2010 at 10:54am
The wording is a bit ambiguous, to me.
Normally, one would want the mole fraction of the solutes, which would be
However, the wording is not as specific as this. As it is worded, one has to inclue the moles of water, so
How do you get moles of water?
moleswater=densitywater * volumewater/molmass water
- AP chemistry - Chem is try, Sunday, October 3, 2010 at 11:12am
i got 1.2 but i don't think i did it right. below is my work:
.03/(1moleH2O+.03molesKBr+.14moles NaCl)= 1.2
moles H2O = (1(47))/47=1
- AP chemistry - Chem is try, Sunday, October 3, 2010 at 11:13am
nevermind,i got .02...did i do this correctly??
- AP chemistry - bobpursley, Sunday, October 3, 2010 at 11:28am
Your math is right, however, in the 3 grams (one significant figure), I suspect the writer was sloppy, and meant at least 3.00 grams
3.00/199=.00151moles. I don't know how you got .03 out of that.
How did you get moles water as 1?
- AP chemistry - Chem is try, Sunday, October 3, 2010 at 11:32am
because 1g water = 1mL water
- AP chemistry - bobpursley, Sunday, October 3, 2010 at 11:34am
Nuts to that.
Moles water= masswater/molmasswater=47g/18g/mol= not 1
- AP chemistry - Chem is try, Sunday, October 3, 2010 at 11:38am
so, i got 6.82 moles of water and plug that in and get .00361, right?
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