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iron (III) ions 7. A solution contains equal concentrations of iron (II) ions an

ID: 592362 • Letter: I

Question

iron (III) ions 7. A solution contains equal concentrations of iron (II) ions and iron hydroxide solution is added and a precipitate forms almost im explain what wil de solution is added and a precipitate forms almost immediayp e theidentty of this precipitate. Fe(OH) K, 1.6x10"; Fe(OH), K s Kp-1.1x10 8. A 500.0 mL solution contains 0, 5M bromide i source provides copper (I) ions. What is the maximum amount of copper (), in mo that can be added to form only one kind of precipitate CuBr K-4.2x10s Cul Kup-5.1x101 9. The Kp of AgCl is 1.77 1010, the Ksp of AgBr is 5.35x1013, and Ksp of Agl is 8.52x10 7. If a solution containing equimolar amounts of NaCl, NaBr and Nal is produced and small amount of AgNO3 is added, what is the most likely precipitate to form first? Explain.

Explanation / Answer

identify which precipitates first

Ksp = [Fe+2][OH-]^2

Ksp = [Fe+3][OH-]^3

then

if saturated

1.6*10^-14 = S*(2S)^2

S = ((1.6*10^-14)/4)^(1/3)

S = 0.00001587

[OH-] = 2*S = 2*0.00001587 = 0.00003174 M

ii)=

Ksp = [Fe+3][OH-]^3

if saturated

1.6*10^-14 = S*(3S)^3

S = ((1.1*10^-36)/27)^(1/4)

S = 4.492*10^-10

[OH-] = 3*S = 3*4.492*10^-10= 1.3476*10^-9 M

Clearly, Fe(OH)3 precipitates first, since it is less soluble, requires les OH- to form a solid