Asked by Tc

You have 100.0 mL of 0.2500 M solution of NaCl sitting in a beaker. After several days you test the solution and find out that it is now 0.3721M. How much water must have evaporated??

I got 67.2 mL but its the wrong answer.. PLS HELP!
Answered by Dr Russ
use mmoles as mmoles at end mus be same as at start.

100.0 ml x 0.2500 M = (final vol) x 0.3721 M

so final volume =
100.0 ml x 0.2500 M/0.3721 M

I got 53.75 ml as the final volume.

hence you can calculate how much water has evaporated.
Answered by Tc
Thank you for your help :) but the correct answer according to my prof was 32.8mL i am not even sure if C is the correct answer or a typo.

I was give 5 options to choose from:
a) concentration can not change because of evaporation
b) 100.0 mL
c) 32.8 mL
d) 67.2 mL
e) 12.2 mL

Answered by Dr Russ
oops
Sorry a typed 100.0 ml x 0.2500 M/0.3721 M but put 0.2000 into my calculator!!

I got 67.186 ml as the final volume.

Yes, so C
Answered by Lisa
what is 4.00g KCI in 40.0mL of solution. give answer to two significant forms
Answered by Anonymous
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