Ni (H2O)6Cl2(aq) + 6 NH3 (aq) [Ni(NH3)6]Cl2(aq) + 6H2O

In aqueous solution nickel ion (Ni2+; Ni(II)) is surrounded by six water molecules

which are actually bonded to the central metal ion. This complex is called the

hexaquanickel(II) ion. When aqueous nickel chloride is precipitated from solution, the nickel

ions carry their six water molecules into the crystals and so solid nickel(II) chloride is

hydrated, has the formula [Ni(H2O)6]Cl2, and is more properly called hexaquanickel(II)

chloride. If ammonia is added to a solution of this salt, ammonia molecules compete with the

water in bonding Ni2+ and, because the ammonia forms a stronger bond than water, the

ammonia replaces the water according to:

The product [Ni(NH3)6]2+

is called hexamminenickel(II) ion. The

hexaammine nickel (II) ion has six ammonia molecules

surrounding the central nickel 2+ ion in an octahedral

arrangement.The nickel ion has an oxidation state of 2+ and each of

the ammonia molecules is neutral, so the overall charge on the

complex ion is: 2+

Procedure:

Weigh anywhere from 200 to 400 mg of nickel chloride.

Dissolve your nickel chloride in roughly 2 mL of deionized water in a testtube.

Go to a fume hood for the next step. Do not smell or touch the aqueous ammonia

solution.

Slowly pour aqueous ammonia (about 5 mL) into testtube. Shake well, cool in an ice

bath.

Check that you have enough crystals formed.

Filter the crystals through filter paper in a Buchner funnel using a suction filtration

apparatus.

Wash the crystals in two stages, first with ice-cold aqueous ammonia, and then with

about 10 mL of ethanol.

Air-dry the crystals on the filter paper by continuing to draw air through them with

the vacuum for 15 minutes.

Table.1.

Mass of [Ni(H2O)

6]Cl

2

Mass of [Ni(NH3)6]Cl

2

Expected Mass of Ni(NH3)6]Cl

2

% Yeild

Characterisation by UV-Visible absorption spectroscopy:

Procedure:

Dissolve ~ 40 mg of Hexamminenickel(II) Chloride in 5 ml water and record

the absorption spectra.

Dissolve ~ 40 mg of Hexaquanickel(II) Chloride in 5 ml water and record the

absorption spectra.

Dilute the sample by adding 20 ml water and record the spectra of the diluted

sample.

Collect data, analyse the spectra and interpret your results.

Fig.1 Absorption spectra of Hexaquanickel(II) Chloride

Fig.2 Absorption spectra of Hexamminenickel(II) Chloride

Fig.3 Absorption spectra of diluted Hexamminenickel(II) Chloride

Characterisation by FT-IR spectroscopy:

Record the IR-Spectra for well dried Hexamminenickel(II) Chloride and

Hexaquanickel(II) Chloride by preparing solid KBr pellets analyse the spectra and

interpret your results.

Fig.4 FT-IR spectra of Hexaquanickel(II) Chloride

Fig.5 -IR spectra of Hexamminenickel(II) Chloride

References:

Reactivity of nickel, James P. Birk , Martha Ronan , Imogene Bennett and Cheri

KinneyJ. Chem. Educ., 1991, 68 (1), p 48

Any general chemistry or Inorganic chemistry book chapters related to co-

ordination chemistry