Question

Hi. In my next experiment I have to obtain several aliquots in such a way that I must transfer the necessary mL of NaOH so that the final concentration is the required one and add the necessary mL of water so that the final volume is 10mL. I have a little doubt with the calculations that I must perform when doing the experiment. Tnks.

Answer 1

You just do your calculation on the basis of moles:

Lets say you have a concentrated solution and its molarity is M

now If you want to prepare a m concentration solution 10 mL(0.010L) solution

find the moles needed in the final solution = moles = molarity x volume in litres = m x 0.010L = 0.01m moles

this much moles must be coming from concentration as the fresh water added won't have any NaOH

calculate volume needed of the concentrated solution to get 0.01m moles

moles = molrity x volume in litres

0.01m moles = M x V

V = 0.01m / M

V = volume of concentrated solution

now total volume = 10 mL of the concentrated solution

volume of water added to the conc. solution to get 10 mL solution

V + v = 10 mL

v = volume of fresh water

v = 10 mL - V

this way volume of fresh water added can be obtained