HELP Aqueous chem question

Question

How do you calculate for the speciation of Cu(II) for freshwater at a pH value of 8.3 as the hardness increases from 20 (soft) to 100 (moderately hard) to 200 (very hard) mg / L as CaCO3? We are told to assume that the total divalent Cu(II) concentration is 10 ug / L.

Answer 1

Hi Jordan B.,

you solve this type of problem just as you would solve any other type of equilibrium problem. You have probably been given K values for various ionic association reactions, such as Cu(II) + H2O = Cu(II)OH + H(+) and Cu(II) + CO3(2-) = Cu(II)CO3 , HCO3(-) = H(+) + CO3(2-) and so on. Here, you merely must work your way methodically through each of the possible complex species formations -- Cu(II)HCO3 (+) , Cu(II)CO3 (including the possibility of that precipitating out!), Cu(II)OH(+) , and so on, then go back and view whether tweaking any of the "starting" ICE concentrations is required, and re-solve, etc. This is the iterative method of solving multiple complexation reactions occuring simultaneously. It may seem clunky and roundabout the first time you do this, but you will acquire both calculation speed and estimation finesse as you process more of these types of problems. Don't make the assumption that "somebody else will solve these / an expert system will solve these for me"; it will almost always take you longer to find a program to do this than it will take you to longhand solve yourself.

Answer 2

Hi Jordan.

Evaluation of speciation of Copper (Cu II) in water at a specific pH and hardness variations is empirical process (experimental outcomes). The determination is not trivial because a model does not exist. Therefore, I suggest please refer to white paper described on internet URL https://academic.oup.com/chemse/article/31/7/689/278058

Title of the paper is

Evaluation of Copper Speciation and Water Quality Factors That Affect Aqueous Copper Tasting Response by J Cuppett, S Duncan, and A Dietrich

I hope this helps.

Sincerely,

Shailesh (Sky) K., Former Professor

University of Pittsburgh, PA

Expert Physics/Chemistry and Math Tutor, WYZANT