# What is "concentration"? How does concentration change when volume changes?

We know that $\text{Concentration"="moles of stuff"/"volume of solution}$,
and thus $C \text{(concentration)"xxV"(volume)"="moles of stuff.}$
Since ${n}_{\text{moles of stuff}}$ is presumed to be constant; i.e. we reasonably assume that you have not added any more solute to the solution, then:
${C}_{1} {V}_{1} = {C}_{2} {V}_{2}$, each side of the equation has units $m o l \times {L}^{-} 1 \times L = m o l$, so this is consistent dimensionally. Is this what you want? Someone here will be happy to expand if I have missed the point of your question.