Question

Another unknown was tested using this procedure. Upon the addition of 6M NH3 and 6M HNO3, no precipitate formed. (NH4)2CO3 was then added. A precipitate formed and the mixture was centrifuged and decanted. The liquid was then transferred to a small beaker and heated to dryness. Once cool, 1M H3PO4 and 1M Na2HPO4 were added to re-dissolve the solid, and the solution was divided into two test tubes. To the first, solid KI was added; no change was observed. To the second, HDMG was added; a red precipitate formed. The solid from the centrifugation was then dissolved in 6M HCl and Na2SO4 was added. A white precipitate formed. The mixture was centrifuged and decanted. 6M NH3 and (NH4)2C2O4 were added to the liquid. A white precipitate formed. Which cations are present in the unknown?

Answer 1

• Upon the addition of 6M NH₃ and 6M HNO₃, no precipitate formed.

No precipitate on addition of 6M NH₃ , It indicates all compounds which indicates compounds which makes insoluble hydroxide (like Al, Fe, Cr) , and Cu absent.

A => (NH₄)₂CO₃ was then added : A precipitate formed   ( Ca²⁺, Sr²⁺, Ba²⁺ may present ₎

This solid from the centrifugation was then dissolved in 6M HCl and Na₂SO₄ was added :  

   A white precipitate formed   :   Ba²⁺             (BaSO₄(s))

          CaSO₄ is soluble in water.

     The mixture was centrifuged and decanted. 6M NH₃ and (NH₄)₂C2O4 were added to the liquid. A white precipitate formed.   : Ca²⁺ present. ( CaC₂O₄ (s))

==> From A :

The liquid was then transferred to a small beaker and heated to dryness.

Once cool, 1M H3PO4 and 1M Na2HPO4 were added to re-dissolve the solid, and the solution was divided into two test tubes.

To the first, solid KI was added; no change was observed.

To the second, HDMG was added; a red precipitate formed.    : (Ni (DMG)₂)

Nickel bis(dimethylglyoximate) is the coordination complex with the formula Ni[ONC(CH3)C(CH3)NOH]2. The compound is a bright red solid .

Ni²⁺ present