Estimation of Nickel(II) Gravimetrically using Dimethylglyoxime (Ni–DMG)

 Estimation of Nickel(II) Gravimetrically using Dimethylglyoxime (Ni–DMG)

Aim

To estimate the amount of nickel(II) present in the given solution by gravimetric method using dimethylglyoxime (DMG).

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Principle

Nickel(II) ions react with dimethylglyoxime (DMG) in ammoniacal medium to form a bright red insoluble complex, nickel dimethylglyoxime Ni(DMG)₂.

The precipitate is filtered, washed, dried and weighed. From the weight of the precipitate, the amount of nickel present in the solution is calculated.

Reaction

$$N{i}^{2+}+2DMG\to Ni(DMG{)}_2\downarrow$$

The precipitate Ni(DMG)₂ is red in colour and insoluble in water.

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Requirements

Chemicals

Given nickel(II) solution, Dimethylglyoxime (DMG) solution, (1%)Ammonium hydroxide (NH₄OH), Distilled water, Ethanol

Apparatus

Beaker, Glass rod, Water bath, Gooch crucible / sintered glass crucible, Filter paper, Oven / hot plate, Weighing balance

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Procedure

1. Take 25 mL of the given nickel solution in a beaker.

2. Add few drops of ammonium hydroxide to make the solution slightly alkaline.

3. Heat the solution gently on a water bath.

4. Add dimethylglyoxime solution slowly with constant stirring.

5. A bright red precipitate of nickel dimethylglyoxime forms.

6. Continue heating for 10–15 minutes to complete precipitation.

7. Allow the precipitate to settle.

8. Filter the precipitate using a pre-weighed Gooch crucible.

9. Wash the precipitate with warm water followed by ethanol.

10. Dry the crucible with precipitate in an oven at about 110°C, cool in a desiccator and weigh.

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Observation Table

Sr. No.	Observation	Value
1	Weight of empty crucible	W₁ g
2	Weight of crucible + precipitate	W₂ g
3	Weight of Ni(DMG)₂ precipitate	(W₂ – W₁) g

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Calculation

Molecular weight of Ni(DMG)₂ = 288.7 g/mol
Atomic weight of Ni = 58.7 g/mol

$$\text{Nickel in precipitate} = \frac{58.7}{288.7} \times \text{Weight of Ni(DMG)}_2$$ $$\text{Amount of Nickel} = \frac{58.7}{288.7} \times (W_2 - W_1)$$

Result

The amount of nickel present in the given solution was determined gravimetrically using dimethylglyoxime method.=