Nickel and its compounds

The electron configuration of nickel

[Ar]4s²3d⁸

Properties of nickel as a transition element

1. Forms colored compounds; for instance, Ni²⁺ is green
2. Has variable oxidation states; +2, +3,
3. Forms complexes, e.g. Ni(NH₃)₆²⁺.
4. Catalytic property: it is a catalyst in the hydrogenation of alkenes, alkyne

Physical Properties

Nickel is a hard metal that is quite lustrous. It melts at 1452⁰C and has a density of 8.90 g cm^-3.  Nickel is used in making of alloys, electroplating of materials; and as a catalyst in the hydrogenation of fats and in making synthesis gas.

The reaction of air with nickel

It reacts slowly at ordinary temperature but vigorously at high temperature to form nickel oxide

2Ni(s) + O₂(g) → 2NiO(g)

The action of water on nickel

Nickel decomposes steam at red heat to hydrogen

Ni(s) + H₂O(g) ↔NiO(s) + H₂(g)

The reaction of nickel with acids

Dilute hydrochloric acid sulphuric acids have slow action on nickel.

But nitric acid readily dissolves the metal.

3Ni(s) + 8HNO₃(aq) → 3Ni(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)

The reaction of nickel with halogen:

Chlorine reacts with nickel to form nickel (II) chloride.

Ni(s) + Cl₂(g) →   NiCl₂(s)

The reaction of nickel with sulphur

Sulpur reacts with nickel to form nickel sulphide

Ni(s) + S(s) →  NiS(s)

Qualitative analysis f nickel II ions

Common nickel II salts

Nickel (II) sulphate, NiSO₄.7H₂O

Nickel (II) carbonate, NiCO₃

(NH₄)₂SO₄.NiSO₄.6H₂O

The reaction of nickel with dilute sodium hydroxide

Forms a green precipitate insoluble in excess

Ni²⁺ (aq) + 2OH^– (aq)  → Ni (OH)₂ (s)

The reaction of nickel with dilute ammonia solution

Forms a green precipitate soluble in excess

Ni²⁺ (aq) + 2OH^– (aq)  → Ni (OH)₂ (s)

Then

Ni(OH)₂(s) + 6NH3(aq) → Ni(NH₃)₆²⁺

Confirming Ni²⁺ ions

Forms a pink ppt on addition of a few drops of ammonia followed by dimethylglyoxime.

Trial 1

When a pale green solid was heated, it decomposed to a green solid, Q, and gas that turned lime water milky was evolved. Q dissolved in dilute nitric acid to give a green solution, R. On addition of dilute sodium hydroxide solution to R, a green precipitate, S, insoluble in excess alkali was obtained. S dissolved in aqueous ammonia to give a purplish-blue solution.

(a) Identify compounds P, Q, S, and solution R.                                             (4 marks)

(b) Write equations for the reactions between;      

(i) Q and nitric acid.   (1½ marks)

(ii) R and sodium hydroxide. (1½ marks)

(iii) S and ammonia.  (2 marks)

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Compiled by Dr. Bbosa Science