Question

Predict the chemical formula for each of the following ternary ionic compounds given the formula of iron(III) sulfate, \(\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}\) (a) cobalt(III) sulfate (b) iron(III) selenate

Short answer

(a) Co₂(SO₄)₃; (b) Fe₂(SeO₄)₃.

Step-by-step solution

Understand Fe₂(SO₄)₃

The provided compound is iron(III) sulfate, \(\text{Fe}_2\left(\text{SO}_4\right)_3\), where iron has a \(+3\) charge and sulfate has a \(-2\) charge.It shows that two iron ions and three sulfate ions balance out their charges to make a neutral compound.

Identify the charge on cobalt(III)

Cobalt(III) means cobalt with a \(+3\) charge. The formula needs to balance three cobalt ions with sulfate ions, \text{SO}_4^{2-}, in the same way as iron(III) sulfate does.

Derive chemical formula for cobalt(III) sulfate

To balance the charges, we need two \(\text{Co}^{3+}\) and three \(\text{SO}_4^{2-}\) ion.So the formula becomes \(\text{Co}_2\left(\text{SO}_4\right)_3\).

Understand selenate ions

Selenate, similar to sulfate, is \text{SeO}_4^{2-}so it’s a polyatomic ion with a \(-2\) charge.

Derive chemical formula for iron(III) selenate

Since iron(III) has a \(+3\) charge, and selenate has a \(-2\) charge, apply the same ratio as \text{Fe}_2\text{(SO}_4\text{)}_3.Thus, the formula is \text{Fe}_2\left(\text{SeO}_4\right)_3.

Key concepts

Iron(III) sulfate

Iron(III) sulfate is a type of ternary ionic compound consisting of iron (Fe) ions and sulfate (SO₄) ions.
In this compound, iron carries a charge of +3, which is often denoted in parentheses as iron(III).
Sulfate is a polyatomic ion with a charge of -2, represented as SO₄²⁻.In the chemical formula - \(\mathrm{Fe}_2\left(\mathrm{SO}_4\right)_3\), there are two iron ions and three sulfate ions.
The formula reflects the fact that the total positive charge is balanced by the total negative charge, making the compound neutral.
This type of charge balancing is crucial in forming stable ionic compounds.
The process involves listing the known charges of the ions and determining their lowest common multiple.
Here, two iron ions total \(2 \times 3 = +6\), and three sulfate ions total \(3 \times -2 = -6\).
Adding these gives a net charge of zero, balancing the compound and ensuring neutrality.

Cobalt(III) sulfate

Cobalt(III) sulfate is similar to iron(III) sulfate, but instead, it involves cobalt ions and sulfate ions.
The name cobalt(III) indicates that cobalt has a +3 charge.
Sulfate, as before, is a polyatomic ion with a -2 charge.To create a neutral ionic compound, the cobalt ions need to match with the appropriate number of sulfate ions to balance the charges.
The steps to achieve this are much like those used for constructing the formula for iron(III) sulfate:

• List the charges: three +3 charges from the cobalt ions and two -2 charges from each sulfate ion.
• Balance the charges: Using the knowledge that two cobalt ions (each with a charge of +3) gives a total charge of +6.
• Thus, three sulfate ions (each with a charge of -2) gives a total charge of -6, which perfectly balances the cobalt's charge.

This results in the formula \(\mathrm{Co}_2\left(\mathrm{SO}_4\right)_3\), following the same logic as iron(III) sulfate.

Iron(III) selenate

Iron(III) selenate involves the combination of iron ions and selenate ions.
The term "iron(III)" shows that the iron ions bear a +3 charge.
Selenate, parallel to sulfate, is a polyatomic ion with a -2 charge, and it is chemically represented as SeO₄²⁻.The way we derive the formula for iron(III) selenate mirrors that used in iron(III) sulfate:

• Iron's +3 charge needs to be counteracted by a selenate's -2 charge to form a neutral compound.
• We do this by following similar charge balancing: we involve two iron(III) ions and three selenate ions.
• This combination yields the formula \(\mathrm{Fe}_2\left(\mathrm{SeO}_4\right)_3\).

Such consistent rules around charge neutrality apply widely in chemistry, demonstrating the importance of understanding ionic charges and partnerships between ions.