Solubility, Precipitation and Dissolution Lead. Pb2^+, is a heavy metal that fre

Question

Solubility, Precipitation and Dissolution Lead. Pb2^+, is a heavy metal that frequently causes concern when it is present in water. Some preliminary calculations are necessary to determine whether it is feasible to precipitate Pb2^+ as the sulfate. In the water, 10^-4 moles/liter of Pb2^+ and 10^-4 moles/liter of SO_4^2- are originally present. p_Ksp of PbSO_4(s) is 7.8. This solution is a) under saturated b) super turbid c) saturated d) super saturated e) over saturated How much Pb2^+ will precipitate (in moles/liter) if 1 times 10^-3 moles of Na_2SO_4 is added per liter of solution? How much SO_4^2+ remains (in moles/liter) after precipitation? How much Pb^2+ remains (in moles/liter) after precipitation? What is the solubility of PbSO_4(s) after the addition of 1 times 10^-3 moles of Na_2SO_4?

Explanation / Answer

Q1.

a)

Ksp = [PB+2][SO4-2]

is

Q > Ksp, then this is supersaturated

Q = [PB+2][SO4-2] = (10^-14)(10^-4) = 10^-8

Ksp = 10^-pKsp = 10^-7.8 = 1.58489*10^-8

Note thjat

Q < KSp, so this is almost saturated, techincially speaking, under saturated

Q2.

[PB2+] requiret to precipitate 10^-3 M Na2SO4 per liter of solution

1.58489*10^-8 = [Pb+2][SO4-2]

[PB+2] = (1.58489*10^-8 )/(10^-3) = 1.58*10^-5

Q3.

find SO4-2 remaining after pecipitation

this will be technically in equilibrium so

Ksp = [Pb+2][SO4-2]

(1.58489*10^-8) = S*S

S = sqrt((1.58489*10^-8) ) = 0.0001258 M

Q4.

ratio is 1:1 so Pb+2 = SO4-2 = 0.0001258

Q5

Solubility of PBSO4 after 10^-3 is added

Ksp = [Pb2+][SO4-2]

1.58*10^-5 = S * (10^-3)

S = 1.58*10^-2 M

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