Question

Write the formulas for the following compounds:
Nickel (II) Sulphate

Answer 1

Hint: To attempt such questions, initially estimate the oxidation states of both the cation and anion and then apply cross multiply method to obtain the formula of the compound.

Complete step by step solution:
As the oxidation state of nickel is given as (II), so charge on nickel will be $+2$ and symbol representation is $N{{i}^{2+}}$. The charge on anion sulphate is $-2$ and symbol representation is \[S{{O}_{4}}^{2-}\].

On cross-multiplying the oxidation states with the symbols of cation and anion, we get the formula as $N{{i}_{2}}{{(S{{O}_{4}})}_{2}}$. But, when there is a common factor between the ions, for example, we have 2 as a common factor, in this case, we eliminate this common factor and the formula becomes $NiS{{O}_{4}}$.
Nickel sulphate could be either anhydrous (without water molecules) or hydrated (with water molecules). There are at least 7 known sulphate salts of nickel (II). The difference between these salts is with respect to either hydration or the crystal habit. One of the common tetragonal hexahydrate nickel salt crystallizes from the aqueous salt solution in between \[30.7{}^\circ -53.8{}^\circ C\]. At a temperature lower than this, the heptahydrate salt crystallizes and at above temperatures orthorhombic hexahydrate forms predominate. The anhydrous form is synthesized by heating the hydrated salts above \[330{}^\circ C\]. All nickel sulphates are paramagnetic in nature.

Additional Information:
Based on patch tests, nickel sulphate was the top allergen in the year 2005-2006. It is also declared as carcinogenic for human beings due to increased respiratory cancer risks reported in epidemiological assessments of the workers from sulfidic ore refineries.

Note: The formulas for hexahydrated nickel sulphate and heptahydrate nickel sulfate salts are $NiS{{O}_{4}}\centerdot 6{{H}_{2}}O$ and $NiS{{O}_{4}}\centerdot 7{{H}_{2}}O$.