I'm having some trouble with this one A water sample contains the following ions (all in mg/L except HCO3-) K+=70, Sr+2=20, Ca+2=180, Mg+2=80, HCO3-=230 mg/L as CaCO3-2, SO4-2=164, NO3-=37, Cl-=400, CO3-2=35, and B=?? has a valence number of 2 but the sign is unknown. TDS(Total Dissolved Solids)=1397 mg/L Assume the water is balanced, identify the missing ion B as being Fe+2, Ba+2, Cd+2 or HPO4-2. So I worked out the Equivalent Weights and converted the concentrations to the respective normalities.Then I added up all the positive and negative normalities and found a difference of 3.21meq/L favouring the anions. My problem is when I work out the mass concentration for the B ion I convert the HCO3- to its mass concentration 280.6 mg/L rather than using its alkalinity of 230 mg/L as CaCO3.However this gives me the wrong answer with a molecular weight of 81.2 which doesn't correspond to anything but I get the right answer if I use 230 and it works out to be Cd+2 because you get a molecular weight of 112.8.so yeah this doesn't make sense.