Test Nickel ion (Ni²⁺) in Qualitative Analysis | Ni Metal Reactions

There are tests for identifying the presence of Nickel +2 (Ni²⁺) ion from other cations. Testing for Nickel ion is done by observing physical characteristics such as colours or formation precipitates or solutions with other reagents. Ni²⁺ cation give aqueous solutions and precipitates. Nickel metal is a 3d block element and it's atomic number is 28. In this tutorial, we will study how to identify Ni²⁺ cation from other cations in qualitative analysis.

Properties and reactions of Nickel metal

Nickel is the 22nd most abundant element in the earth's crust and occurs in a variety of sulfide ores. General configuration of nickel is 4s² 3d⁸. Major oxidation state (oxidation number) of nickel is +2. Nickel is a silvery metal that has a beautiful high polish.

Properties of nickel metal

• Nickel react with dilute acids to form hydrogen gas and Ni²⁺ ion.
• Nickel is a silvery white metal
• No reaction between nickel and moisture in air
• Powdered nickel readily reacts with carbon monoxide (CO) at normal conditions to form tetracarbonylnickel(0) ( [Ni(CO)₄] ) complex. In this complex, oxidation number of Ni is zero.
  Ni_(s) + 4CO_(g) → [Ni(CO)₄]_(g)

Reactions of nickel metal

Nickel and acids reaction

Nickel is soluble in dilute acids such as HCl or dilute H₂SO₄ to form green colour solution hexaaquanickel(II) ion ( [Ni(H₂O)₆]²⁺ ) and hydrogen gas (H₂).

Ni_(s) + 6H₂O_(l) + 2H⁺_(aq) → [Ni(H₂O)₆]²⁺_(aq) + H_2(g)

If an alkali such as aqueous NaOH is added to this green colour solution, a green colour precipitate, Nickel hydroxide ( [Ni(OH)₂(H₂O)₄] ) is formed.

Qualitative Analysis Tests of nickel ion and compounds

When we testing nickel ion and it's compounds we should have a knowledge of whether those compounds are precipitates or solutions and colours of them. Which are important to identify nickel ion from other metal ions. We discuss few examples of identifying nickel ion from other cations.

Testing Nickel ion with aqueous ammonia solution | Ni²⁺ + NH₃

Slowly add aqueous ammonia solution to aqueous nickel +2 ion solution. Nickel hydroxide, ( Ni(OH)₂ ), a light green precipitate forms. When add excess ammonia solution, Nickel hydroxide precipitate dissolve and give blue colour solution due to formation of hexaamminenickel(II) ion ( [Ni(NH₃)₆]²⁺ ) coordination complex. If you add concentrated ammonia solution, intensity of blue colour increases.

Testing for nickel(ii) ion with Hydrogen sulfide and | H₂S + Ni²⁺

Under acidic conditions: Send hydrogen sulfide (H₂S) gas under acidic conditions to a nickel(ii) ion solution. But, expected precipitate if Nickel sulfide is not formed.

Under alkaline conditions: Send Hydrogen sulfide gas in the presence of NH_3(aq)/NH₄Cl to the nickel(ii) ion solution. Then you can observe Nickel sulfide (NiS) ,a black precipitate is formed.

Similar to the above reaction, you can add Ammonium sulfide ( (NH₄)₂S ) to nickel(ii) ion solution. It also gives NiS ,the black precipitate.

Testing of Nickel ion with chloride ion

Ni²⁺_(aq) ions reacts with concentrated chloride (Cl^-) ions in the presence of ethanol medium to give tetrachloronickel(II) ion / [NiCl₄]^2-, a blue colour solution.

Ni²⁺_(aq) ions reacts with concentrated chloride (Cl^-) ions in the presence of acids to give tetrachloronickel(II) ion / [NiCl₄]^2-, a yellow brown solution. [NiCl₄]^2- is a tetrahedral coordination complex.

Nickel ion and nitrile ions

Ni²⁺_(aq) ions reacts slowly with nitrile ions (CN^-) to give nickel cyanide / [Ni(CN)₂], which is a light green precipitate.
This precipitate will dissolve in excess CN^- to form tetracynonickel(II) ion / [Ni(CN)₄]^2-, yellow colour solution.

Nickel dimethylglyoxime complex test

Add dimethylglyoxime(DMG) to nickel ion solution. Next add little bit of ammonia to make solution basic. It will give a red precipitate.

This is a very specific test for nickel +2 cation.

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Questions of nickel ion tests under qualitative analysis of inorganic chemistry

What tests can be done to identify solid nickel hydroxide and chromium hydroxide?

Chromium hydroxide and nickel hydroxide are green precipitates. So we cannot identify them from looking their colours and dissolving in water.

But we have learnt about amphoteric compounds and elements. In that lesson, you may have learnt that, chromium hydroxide is an amphoteric hydroxide. But nickel hydroxide is not an amphoteric hydroxide. But both of these hydroxides have basic characteristics.

We are going to check amphoteric characteristics of these two hydroxides by adding aqueous NaOH. Chromium hydroxide should dissolve when add NaOH more and more. From that, we can identify nickel hydroxide and chromium hydroxide.

Determination of nickel +2 ion?

Aqueous Ni²⁺ solution is green colour. When adding aqueous NaOH, a green precipitate is given and with addition of excess aqueous NaOH, precipitate does not dissolve. But addition of aqueous NH₃, blue colour solution [ Ni(NH₃)₆]²⁺ is given.

What are the precipitates of nickel ion and give their colours?

• Nickel hydroxide - Ni(OH)₂ - green
• Nickel carbonate - NiCO₃ - Green
• Nickel cyanide - Ni(CN)₂ - Yellow brown
• Nickel sulfide - NiS - black

Metal precipitates and colours

What is the colour of nickel ion in aqueous state?

Nickel (+II) ion gives a green colour solution in aqueous state.

3d metal ions compounds colours

What ions nickel metal form?

Major oxidation state of nickel metal is +2.

Is nickel metal a catalyst? If it is give examples.

Yes. Nickel is used as a catalyst in different applications in the chemical industries.

• In hydrogenation of vegetable oils.
• For hydrogenation of alkenes and alkynes. Alkenes and alkynes can be hydrogenated to alkanedd from in the presence of nickel metal with hydrogen gas.