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### Fundamentals: G#25

Posted: Tue Oct 01, 2019 4:34 pm
hey guys!

i have a question for #25 in the G section for fundamentals. it's asking how many molecules will be present in 10. mL of the final solution after diluting 10. mL with a concentration of 0.10 mol L^-1 90 times.

i remember a key concept was that moles stays the same during dilutions. does that mean that molecules also stay the same? even if the solution is diluted 90 times?

thank you!

### Re: Fundamentals: G#25

Posted: Tue Oct 01, 2019 4:40 pm
Hello. Yes, the moles are representative of how many molecules are in a solution and therefore both of moles of a substance and the amount of molecules of such substance would remain the same during dilution. The only amount that would change during the dilution process would be the amount of moles per liter, but collectively the moles of a substance would not change as long as none of the solution is removed or more of the solute isn't added. Hope this helps!

### Re: Fundamentals: G#25

Posted: Tue Oct 01, 2019 4:45 pm
Adding on to that, the number of molecules stays the same, but the question is tricky because it's really looking for the molarity of the solution. Since the solution is diluted so much, the volume becomes so large, that no matter how many moles there are, it ends up becoming close to zero because the denominator is so large. (M = moles/volume) So while it seems like the question is asking how many molecules there are, it's really asking how strong the molarity is of the solution, which is why the answer is that there is virtually no X left because the molarity is close to zero.