- #1

Adesh

- 735

- 191

- Homework Statement
- Concentration of solids and liquids are constant, but it seems to me non-intuitive.

- Relevant Equations
- concentration = density/ molar mass

I was introduced to the concepts like molarity, molality , mole fraction, formality, normality etc. during general chemistry and it was said that these concepts are used to measure the concentration of solutions. But as the thing called

I did some research and found that people are explaining it like this :-

Let's assume that you have a liquid with density [itex]\rho[/itex] and molar mass [itex]m[/itex] and since units of [itex]\rho[/itex] is [itex]\frac{g}{L}[/itex] and that of [itex]m[/itex] is \frac{g}{mol} therefore [itex]\frac{\rho}{m}[/itex] will have units as[itex] \frac{mol}{L}[/itex] and hence [itex] concentration = \frac{\rho}{m}[/itex] and [itex] \rho= \frac{mass}{volume} [/itex]. Therefore, [itex] conc. = \frac{mass\cdot molar mass}{volume}[/itex] and as you can see all three quantities are constant(volume is constant for solids and liquids) and hence the concentration of solids and liquids are constant.

I agree with that mathematical explanation but what does it mean when we say

Any help will be much appreciated. I know that I'm having some misconception and therefore I request you all to please help me.

Thank you.

**Chemical Equilibrium**came I was surprised when I read "*In heterogenous chemical reaction the concentration of solids and liquids are taken to be constant in calculating [itex]K[/itex]"*I did some research and found that people are explaining it like this :-

Let's assume that you have a liquid with density [itex]\rho[/itex] and molar mass [itex]m[/itex] and since units of [itex]\rho[/itex] is [itex]\frac{g}{L}[/itex] and that of [itex]m[/itex] is \frac{g}{mol} therefore [itex]\frac{\rho}{m}[/itex] will have units as[itex] \frac{mol}{L}[/itex] and hence [itex] concentration = \frac{\rho}{m}[/itex] and [itex] \rho= \frac{mass}{volume} [/itex]. Therefore, [itex] conc. = \frac{mass\cdot molar mass}{volume}[/itex] and as you can see all three quantities are constant(volume is constant for solids and liquids) and hence the concentration of solids and liquids are constant.

I agree with that mathematical explanation but what does it mean when we say

*"that bottle have concentrated NaOH and that bottle have dilute NaOH"*isn't it contrary to what has been just described above? I mean if we mix more [itex] CaO[/itex] in water we will get a highly concentrated solution then if we mix just a pinch of [itex]CaO[/itex] in water.Any help will be much appreciated. I know that I'm having some misconception and therefore I request you all to please help me.

Thank you.