Question

Predict the chemical formulas of the ionic compound formed by (a) \(\mathrm{Fe}^{3+}\) and \(\mathrm{OH}^{-}\), (b) \(\mathrm{Cs}^{+}\) and \(\mathrm{NO}_{3}^{-},(\mathbf{c}) \mathrm{V}^{2+}\) and (e) \(\mathrm{In}^{3+}\) and \(\mathrm{O}^{2-}\). \(\mathrm{CH}_{3} \mathrm{COO}^{-},(\mathbf{d}) \mathrm{Li}^{+}\) and \(\mathrm{PO}_{4}^{3-}\),

Short answer

The chemical formulas of the ionic compounds formed by the given ions are: (a) Fe(OH)₃, (b) CsNO₃, (c) V(CH₃COO)₂, (d) Li₃PO₄, and (e) In₂O₃.

Step-by-step solution

(a) Fe³⁺ and OH⁻

To make the compound neutral, we need to have equal positive and negative charges. Here, we have Fe³⁺ with a charge of +3 and OH⁻ with a charge of -1. We can balance the charges by having three OH⁻ ions for each Fe³⁺ ion. Therefore, the chemical formula for the ionic compound formed by Fe³⁺ and OH⁻ will be Fe(OH)₃.

(b) Cs⁺ and NO₃⁻

In this case, both the ions have a single charge, with Cs⁺ having a charge of +1 and NO₃⁻ having a charge of -1. Since they have equal and opposite charges, the chemical formula for the ionic compound formed by Cs⁺ and NO₃⁻ will be CsNO₃.

(c) V²⁺ and CH₃COO⁻

Here, we have V²⁺ with a charge of +2 and CH₃COO⁻ with a charge of -1. To balance the charges, we need two CH₃COO⁻ ions for each V²⁺ ion. Therefore, the chemical formula for the ionic compound formed by V²⁺ and CH₃COO⁻ will be V(CH₃COO)₂.

(d) Li⁺ and PO₄³⁻

In this case, we have Li⁺ with a charge of +1 and PO₄³⁻ with a charge of -3. To balance the charges, we need three Li⁺ ions for each PO₄³⁻ ion. Therefore, the chemical formula for the ionic compound formed by Li⁺ and PO₄³⁻ will be Li₃PO₄.

(e) In³⁺ and O²⁻

Here, we have In³⁺ with a charge of +3 and O²⁻ with a charge of -2. To balance the charges, we can use the lowest common multiple (LCM) of 3 and 2, which is 6. We need two In³⁺ ions (each with a charge of +3, for a total charge of +6) and three O²⁻ ions (each with a charge of -2, for a total charge of -6) to balance the charges. Therefore, the chemical formula for the ionic compound formed by In³⁺ and O²⁻ will be In₂O₃.

Key concepts

Chemical Formula Prediction

Predicting the chemical formula of an ionic compound involves understanding how ions combine to form a neutral compound. The key is to balance the charges of the cations and anions involved. When ions combine, their charges must add up to zero, ensuring the compound is electrically neutral.

For instance, when forming a compound from Fe³⁺ and OH⁻, we note that Fe³⁺ has a charge of +3 and OH⁻ has a charge of -1. We need three OH⁻ ions to balance the charge of one Fe³⁺ ion. This results in the formula Fe(OH)₃.

Keep in mind that each situation may be different, but the underlying principle remains the same: adjust the ratio of ions to achieve a net zero charge.

Charge Balancing

Charge balancing is crucial in forming stable ionic compounds. Each ion carries a specific charge depending on the number of electrons lost or gained. In a compound, the total positive charge from cations must equal the total negative charge from anions.

For example, when combining Cs⁺ and NO₃⁻ ions, both have charges of +1 and -1, respectively. The charges naturally balance, so only one of each ion is needed, resulting in the formula CsNO₃. However, if V²⁺ is paired with CH₃COO⁻, the charge on V is +2, and on CH₃COO⁻ is -1. We need two acetate ions to balance one vanadium ion, giving us V(CH₃COO)₂.

Balancing charges is often a straightforward process but requires careful attention to each ion's specific charge.

Valency in Ions

Valency refers to the ability of an ion to combine with others and is directly linked to its charge. The valency of an ion indicates how many bonds it can form with ions of opposite charge.

For example, Li⁺ has a valency of +1, while PO₄³⁻ has a valency of -3. To balance these ions, three Li⁺ ions are needed for every one PO₄³⁻ ion, resulting in the formula Li₃PO₄. Understanding valency is crucial for predicting how ions will pair and what the resulting formula will be.

Valency isn't limited to single atoms; it also applies to groups of atoms acting as a unit, such as polyatomic ions.

Polyatomic Ions

Polyatomic ions are clusters of atoms that behave as a unit and carry a charge. They are an essential part of ionic compound formation. Common examples include NO₃⁻ (nitrate) and CH₃COO⁻ (acetate).

Let's take the example of In³⁺ and O²⁻. Here, In³⁺ has a charge of +3, and combining with O²⁻, we need to consider the amounts that will balance total charges. We will need two indium ions and three oxide ions to make the charges equal zero, forming the compound In₂O₃.

Polyatomic ions often appear in various combinations, so familiarizing yourself with their names and charges can simplify predicting chemical formulas.