Express each aqueous concentration in the unit indicated. a). 25 mg of trichloroethylene in 9.5 l of water, as ppb of trichloroethylene b). 38 g cl2 in 1.00x 104 l of water, as ppm cl2 c). 2.4 ppm f -, as molarity of fluoride ion, in [mol f - /l] d). 45 ppm no3 -, as molarity of nitrate ion in [mol no3 - /l] e). why do some scientists prefer to express concentrations of water contaminants in the units ppm and ppb rather than molarity