# How to calculate concentrations and what is the concept of 'mole'?

Say I have a $50~\mathrm{ml}$ solution of a liquid mixture which is $30~\%$ concentrated. Now if I take $20~\mathrm{ml}$ of that liquid out from that mix, what would be the resulting concentration of both the liquid remaining and the liquid extracted? Will the concentration of both still be $30~\%$?

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– bon
Nov 30, 2015 at 20:50
• What do you think? Please provide your thoughts so we can guide you better. Nov 30, 2015 at 20:50
• According to me the concentration should remain the same since it is dependent on moles and hence even if we take out 20ml from a concentrated solution the moles should not be affected. However my doubt lies in the fact that does this stand true in all terms of concentration , eg in cases of molarity or maybe volume by volume concentrations etc Nov 30, 2015 at 20:53
• @SushmitaNayak yes, if it is a solution all portions will have the same concentration. If it is merely a "mixture", like orange juice, then not necessarily. Nov 30, 2015 at 20:55
• @SushmitaNayak the main concept is that all samples, portions, subdivisions, etc. of a solution have the same concentration. Nov 30, 2015 at 20:58

## 1 Answer

Concentration of a liquid can be given by the formula C=N/V, where V is the volume of the solution and N is the number of moles present in it.

To help you understand exactly what a 'mole' is, think of it like this: when you ad a certain amount of powder to water, say sugar or a fruit drink, how many spoons/ grams of powder you add is the number of moles. (1 mole is actually 6.02214129 * 10^23 particles of the substance)

The concentration can be determined by how much water you add to the drink: If you add more water, the solution is said to be diluted, since the ratio of solute:solvent is lower. So in a drink with 30% concentration, the ratio would be 3:7, 3 moles of powder for 7 moles of water. The concentration can ONLY BE CHANGED if the amount of water changes. The ratio remains same throughout, so concentration would be 30% if you take 20ml, 10ml, or any measurement of volume.

Hope this train of thought helped your mind to get the reasoning :)