Is Molarity constant? My friend and I were debating about if Molarity is constant in a disolution if this one changes volume due to evaporation.
There was this problem that stated that 125 [mL] of sodyum chloride 0.122 [M] evaporates over time and final volume becomes 113 [mL]
I say Molarity keeps being constant, he says no because volume changes.
What do you think?
As molarity is defined as the ratio of molar amount of the dissolved solute and solution volume:
$$c=\frac nV$$
molarity increases when solvent ( like water ) evaporates.
Molarity can be considered constant only in context of later refilling the evaporated solvent and mixing the solution. Then molarity returns to the original value. It assumes the solute ( like sodium chloride ) content is constant, not undergoing any reaction.