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..
