i am having a hard time with D) number one. D. Sulfide Precipitation Precipitati

Question

i am having a hard time with D) number one.

D. Sulfide Precipitation Precipitation of Sulfides. We know that sodium sulfide is a strong electrolyte, so it ionizes completely. (R18) Na2S(aq) 2Na (aq) S (aa) cu (aq) will form a sulfide precipitate, CuS (s) with the US under appropriate conditions. Important note about i The addition of S2 reduces iron(III) to iron (ID: 3+ (aq) 3S (aq) (R19) 2FeS(s) S(s) The black iron (ID sulfide is soluble in dilute nitric acid, which allows the white-yellow sulfur precipitate to be visible. Now try this with each of the seven metal cations K, Ba zn t, Mn t, Co2 Ni Fe 1, write out the correspoding solubility equilibrium equations that would give rise to a sulfide precipitate. Chose the appropriate arrow or depending on solubility. In the lab, try to form the sulfide precipitates with 0.1 MNa2S.

Explanation / Answer

D)

first, identify which will precipiate, those are with Ksp valus

S-2

BaS; ZnS, MnS, CoS, NiS, Fe2S3

therefore, most of them but K+ , Ba+2

reactions

ZnS(s) <--> Zn+2 + S-2(aq)

MnS(s) <--> Mn+2 + S-2(aq)

CoS(s) <--> Co+2 + S-2(aq)

NiS(s) <--> Ni+2 + S-2(aq)

Fe2S3(s) <--> 2Fe+3 + 3S-2(aq)

now...

for a Sulfide concentration of Na2S --> 0.1 M of S-2

then

Ksp values are all above 10^-10

therefore, 0.1 M of S-2 is much liekely going to preciptiate anything with a concentration smaller than 10^-10 M

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