Molar concentration of species $i$ $(C_i)$ $=\frac{no.\ of\ moles\ of\ species\ i (N)}{unit\ volume\ of\ the\ mixture(V)}$ Molar concentration of the mixture is $C = \sum_i^N C_i$ relation to [[Mass Concentration]] of species $i$ is $\rho_i = C_i \times w_i$ where $w_i$ is the molecular weight of the species $i$