For example if the solute of the solution contains $\pu{0.5 mol}$ and the total volume is $\pu{0.5 L}$, the molarity would be $\pu{1M}$. But if I take a portion of that solution, let's say $\pu{0.1 L}$, would that molarity be still $\pu{1M}$? If it were that way, the solute would be $\pu{0.1 mol}$ too.

Or, do the moles of the solute stay the same $\pu{0.5 moles}$ and the molarity would change to $\pu{5M}$?

So my question is, does the solute decrease when the volume decreases too?

  • $\begingroup$ If the concentration of the whole soln is 1M, then a portion taken out remains 1M unless you do something to it. $\endgroup$ – Waylander Nov 27 '18 at 18:06
  • $\begingroup$ So the solute would be 0,1 moles in 0,1L of the the dissolution, right? Because the concentration would be 1M? $\endgroup$ – Sirena S. C. Nov 27 '18 at 18:08
  • $\begingroup$ Correct. If you concentrate it down to dry you would expect to get 0.1 moles of the solute $\endgroup$ – Waylander Nov 27 '18 at 18:22
  • $\begingroup$ Or if I take out a portion of it to mix it with another dissolution, right? $\endgroup$ – Sirena S. C. Nov 27 '18 at 18:24
  • $\begingroup$ Exactly so. If you take out 50ml to react with something else, that 50ml is at a concentration of 1M $\endgroup$ – Waylander Nov 27 '18 at 18:25

No, solute will not decrease if volume will decrease.But molarity will increase for sure, cause molarity is the amount of solute in litre of solution.

Consider container A in which you took 1 litre of water and added two spatulas of NaCl and in another container B you took 0.5 litre of water and added two spatulas of NaCl. Now which container has greater amount of solute , the second one that is container B ,hence molarity of container B solution will be greater than container A.

Hope it will work to clear concept.

  • $\begingroup$ Yeah I get that, but I'm talking about only ONE glass of a dissolution. $\endgroup$ – Sirena S. C. Nov 27 '18 at 18:41
  • $\begingroup$ Well, no. Unless you are doing a different experiment. If you have a homogeneous solution the molarity remains the same unless you do something to it. If you dissolve the same amount of solid in a smaller amount of liquid then you are right, but that wasn't the question. $\endgroup$ – matt_black Nov 27 '18 at 21:18

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