Copper is employed as piping in many domestic and industrial potable water syste

Question

Copper is employed as piping in many domestic and industrial potable water systems. Copper

ions are toxic and the EPA (Environmental Protection Agency) standard limits the copper

concentration of potable water to 1.2 ppm. The potable water supplied by the East Bay

Municipal Utility District (EBMUD) is obtained from snowmelt of the Sierra Nevada mountains

and is of very high purity with a pH near 7. In water of pH 7 the corrosion rate of copper is too

high. In order to minimize corrosion of copper piping, EBMUD, which provides water to

Berkeley as well as to a number of other East Bay communities, adjusts the water’s pH to a value

between 8 and 9 by adding lime (CaO) to the water. Based on the following information, explain

why EBMUD adjusts the pH of its water to 8-9.

Cu+++ H2O <-> CuO (S)+ 2H+ Kd= 1.2882x10-8 M

CuO(S)+ H2O <-> HCuO-2 + H+    Kd= 1.479x10-19M2

2. Copper is employed as piping in many domestic and industrial potable water systems. Copper ions are toxic and the EPA (Environmental Protection Agency) standard limits the copper concentration of potable water to 1.2 ppm. The potable water supplied by the East Bay Municipal Utility District (EBMUD) is obtained from snow melt of the Sierra Nevada mountains and is of very high purity with a pH near 7. In water of pH 7 the corrosion rate of copper is too high. In order to minimize corrosion of copper piping, EBMUD, which provides water to Berkeley as well as to a number of other East Bay communities, adjusts the water's pH to a value between 8 and 9 by adding lime (CaQ) to the water. Based on the following information, explain why EBMUD adjusts the pH of its water to 8-9. W? Cu++ + H2O ÇUQts) + 2H- ?d = 1.2882x 10-8 M CuO(s) + H2O HCuOz + H+ Kd= 1.479x 10-19 MP

Explanation / Answer

As given in the question itself that copper ions are toxic and its concentration is kept low(1.2ppm).

Now at pH of 7, the corrosion rate of copper is high that means water is going to become more toxic. So pH of water needs to be adjusted which as specified in the question is done by adding CaO.

Now both 1st and 2nd reaction are reversible equilibrium reaction and also the reaction will shift in that direction which maintains equilibrium according to Le Chateliars principle.

Now by addition of CaO, the concentration of H+ decreases so the reaction 1 will shift towards right side so the Cu+2 is consumed making water less drinkable(less toxic).

Also, the 2nd reaction which is actually a lot slower than 1st reaction will also shift to the right as CuO concentration increases which in turn make 1st reaction to shift right side decreasing the cu2+ concentration further.

Thus by maintaining the pH around 8-9, the concentration of Cu+2 can be reduced.

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