Describe the difference between concentrated and dilute at the molecular level??

2 Answers
Aug 4, 2017

Hard to know what you are after, but let's define #"concentration"# first......


The typical description of #"concentration"# is #"amount of solute per unit volume"#, and thus we typically use concentration terms of....

#"Molarity"="Moles of solute"/"Litres of solution"#

#"Molality"="Moles of solute"/"Kilograms of solvent"#
(here we have the quotient, moles of solute per MASS of solvent).

#"% by mass"="Mass of solute"/"Mass of solution"xx100%#

or even........

#"parts per million, ppm"="mg of solute"/"litres of solution"#.

Depending on the problem you have, sometimes a value of #"solution density"# is required, i.e. #rho="Mass of solution"/"Volume of solution"#, for you to work out equivalent masses.

Solutions commonly form in the gas phase (including the air we breathe), and in the liquid phase. Solutions in the SOLID phase are also known, and a good example of these materials are #"alloys"#, which are ubiquitous in materials chemistry.

Anyway, to answer your question (FINALLY!), if we dilute a solution, effectively we add more solvent, more dispersing medium, and the denominator in the quotient becomes LARGER. And thus the concentration becomes SMALLER, whatever units you use. Capisce?

Aug 4, 2017

Well, at the 'molecular' level, I would describe it like so...

Take an aqueous solution as an example...

A more "concentrated" solution has the particles closer together than a less "concentrated" solution, i.e. there are more particles per unit volume, the most fundamental/general definition of concentration:

#"conc." = "Number of particles"/"unit volume"#

To dilute the solution, it is easiest to add solvent.

The solvent surrounds the solute particles, literally separating them from each other.

The more solvent there is, the more segregated the solute particles become (the harder it is for them to find each other), and thus the less concentrated (more dilute) the solution becomes.

In other words, more solvent = higher volume of solution = more dilute or less concentrated solution.

(One easy way to demonstrate this is to see how bland soda tastes when you add a bunch of water to it. The taste was diluted.)