Nickel ion testing is done by identifying colours nickel metal compounds or forming precipitates or solutions with other reagents. Nickel metal is placed in 3d block and it's atomic number is 28.
In this tutorial, we study about followings.
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.
Nickel is soluble in dilute acids such as HCl or dilute H2SO4 to form green solution
hexaaquanickel(II) ion /
[Ni(H2O)6]2+ and hydrogen gas (H2).
Ni(s) + 6H2O(l) + 2H+(aq) → [Ni(H2O)6]2+(aq) + H2(g)
If an alkali, NaOH is added to this green solution, a green precipitate, [Ni(OH)2(H2O)4] is formed.
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.
Add aqueous ammonia solution to aqueous nickel ion solution. Nickel hydroxide, ( Ni(OH)2 ), a light green precipitate forms. When add excess ammonia, 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.
Send hydrogen sulfide (H2S) under acidic state to nickel(ii) ion solution. But a precipitate doesn't form.
Send H2S when NH3(aq)/NH4Cl are exist in nickel(ii) ion solution. Then you can see a Nickel sulfide (NiS) ,a black precipitate is formed. Also add (NH4)2S to nickel(ii) ion solution. It also gives NiS ,the black precipitate.
Ni2+(aq) ions reacts with concentrated 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 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.
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.
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 testing reaction of nickel ion.
Questions of nickel ion tests under qualitative analysis of inorganic chemistry
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.
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.
Nickel (+II) ion gives a green colour solution in aqueous state.3d metal ions compounds colours
Major oxidation state of nickel metal is +2.
Yes. Nickel is used as a catalyst in different applications in the chemical industries.
Qualitative Analysis for anions and cations