Aging water distribution infrastructure ia a water quality concern that can affe

ID: 1068573 • Letter: A

Question

Aging water distribution infrastructure ia a water quality concern that can affect human health

and the aesthetic water quality. Eighty-year old galvanized iron pipe in a water distribution

system has experienced corrosion. Corrosion deposits from scales that collect on the pipe contain

high concentrations of soluble iron (II). This iron can be released into the water flowing through the pipe.

....

Assume the water flowing through the pipe contains 10-2 M Na2CO3 at pH 8.3.

How much soluble iron(II) can be released into the water before FeCO3 precipitate forms?

The solubility product of FeSO3 is Kso= 10-10.7

ANSWER

NOTE : Solubility product of FeCO3 should have been given, you have written FeSO3. So we suppose it as FeCO3. FeCO3 <-------> Fe2+ + CO32- ======1)

Let S be the solubiliy of FeCO3

Ksp = [Fe2+ ][CO32-] = (S)2 = 10-10.7

S= 4.5 X 10-6

Na2CO3 dissiciates as

Na2CO3 -------> 2Na+ + CO32-

10-2M -------- 10-2M 10-2M

Inserting the value of concentration of CO32- in equilibrium 1)

FeCO3 <-------> Fe2+ + CO32-

Ksp = [Fe2+ ][CO32-] = 10-10.7

[Fe2+ ][10-2] = 10-10.7

[Fe2+ ] = 10-10.7 / 10-2 = 2.0 X 10-9M

Hence 2.0 X 10-9M of iron(II) can be released into water before precipitation of FeCO3