What inferences can be made? NaOH was added to a blue-green solution (Fe3+, Ni2+, Mn2+, Cr3+,...

What inferences can be made? NaOH was added to a blue-green solution (Fe³⁺, Ni²⁺, Mn²⁺, Cr³⁺, and/or Zn²⁺). After stirring, the solution appeared light green with no precipitate.

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Expert Solution

All given acidic radicals (Fe³⁺, Ni²⁺, Mn²⁺, Cr³⁺, Zn²⁺) on addition of strong base NaOH forms there hydroxides which may or may not be soluble in NaOH solution depending on their solubility product(Ksp) values.

Fe³⁺ (aq.) + 3OH^-(aq.) ------> Fe(OH)₃ (ppt.)[Ksp = 3.8 x 10^-38]

Ni²⁺ (aq.) + OH^-(aq.) ------> Ni(OH)₂

Mn²⁺ (aq.) + 2OH^-(aq.) ------> Mn(OH)₂ (ppt.)

Cr³⁺ (aq.) + 3OH^-(aq.) ------> Cr(OH)₃(ppt.)[Ksp= 2.9 x 10^-29]

Zn²⁺ (aq.) + 2OH^-(aq.) ------> Zn(OH)₂

But observation says no precipitation occurred hence following inferences can be drawn,

1)III-group radicals Fe³⁺ and Cr³⁺ are certainly absent in the solution as there hydroxides are insoluble in water and in basic (excess NaOH) solutions.

2) IV-group radicals Mn²⁺ and Ni²⁺are also certainly absent as their hydroxides also do not dissolved in even excess NaOH (Basic) solution.

3)IV-group radical Zn²⁺ may present because its hydroxide Zn(OH)₂ is soluble in excess NaOH solution by forming sodium zincate (Na₂ZnO₂ or Zn(ONa)₂) which might have faded the color of solution to light green.

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queen_honey_blossom answered 1 year ago

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