There are various forms of the concentration expression,
#"mass of stuff"/"volume of solution"#, #"mass of stuff"/"mass of solution"#. Most commonly used is #"molarity"="moles of stuff"/"volume of solution"#...and units of #mol*L^-1# result. Weaker concentrations CAN be quoted in terms of #"parts per million"#...#"1 ppm"-=1*mg*L^-1("of AQUEOUS solution")#..
The product, #"volume (L)"xxmol*L^-1# gives an answer in #mol#..
Unless, you are given the composition of the solution, i.e. #10*g# of #HCl# is dissolved in enuff water to give #1*L# of solution, you are usually quoted solution concentration. In these circumstances we would take....
#((10*g)/(36.46*g*mol^-1))/(1*L)=0.274*mol*L^-1#...WITH RESPECT to #HCl#...of course the acid speciates in solution..to give #[H_3O^+]=[Cl^-]=0.274*mol*L^-1#..
