Question

Predict the chemical formula for each of the following ternary ionic compounds given the formula of sodium sulfate, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (a) francium sulfate (b) sodium sulfite

Short answer

(a) Francium sulfate: (\mathrm{Fr}_{2} \mathrm{SO}_{4}\) (b) Sodium sulfite: (\mathrm{Na}_{2} \mathrm{SO}_{3}\)

Step-by-step solution

Understanding the Compound Structure

A ternary ionic compound consists of three different elements. For sodium sulfate, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), the compound contains sodium (Na), sulfur (S), and oxygen (O). Sodium sulfate is created by combining two sodium ions (Na⁺) with a sulfate ion (SO₄²⁻). The sulfate ion has a charge of -2.

Identifying Charges of the New Elements

For francium sulfate, we need to replace sodium (Na) in sodium sulfate with francium (Fr). Francium, like sodium, is in Group 1 of the periodic table and thus has a charge of +1 (Fr⁺). Similarly, for sodium sulfite, we replace the sulfate ion with the sulfite ion (SO₃²⁻), which also has a charge of -2.

Balancing Francium Sulfate

Since francium has a charge of +1 and sulfate has a charge of -2, we need two francium ions to balance one sulfate ion, just like in sodium sulfate. Therefore, the formula is \(\mathrm{Fr}_{2} \mathrm{SO}_{4}\).

Balancing Sodium Sulfite

With sodium (Na⁺) having a charge of +1 and sulfite (SO₃²⁻) having a charge of -2, we similarly need two sodium ions to balance one sulfite ion. The compound formula is then \(\mathrm{Na}_{2} \mathrm{SO}_{3}\).

Key concepts

Chemical Formula

A chemical formula is a simple way to express the composition of a compound. It uses symbols to represent elements and subscripts to show the number of atoms of each element in the compound. For example, in the chemical formula for sodium sulfate, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), \(\mathrm{Na}\) stands for sodium, \(\mathrm{S}\) for sulfur, and \(\mathrm{O}\) for oxygen.
The subscript '2' next to \(\mathrm{Na}\) indicates that there are two sodium atoms, while \(\mathrm{SO}_{4}\) represents the sulfate ion, which is made up of one sulfur atom and four oxygen atoms. Chemical formulas provide crucial information about the type and ratio of elements in a compound. This is vital for predicting the compound's properties and reactions. It is essentially the identity card for the compound, making it essential for studying chemistry.

Ion Charges

Ion charges refer to the electrical charge that an atom carries when it loses or gains electrons. These charges affect how ions combine to form compounds. A positive charge indicates a loss of electrons, while a negative charge shows a gain of electrons.
In the case of sodium sulfate, sodium (\(\mathrm{Na}\)) is a Group 1 element, which means it typically loses one electron to carry a positive charge (\(\mathrm{Na}^+\)). On the other hand, the sulfate ion, \(\mathrm{SO_{4}^{2-}}\), carries a negative charge of -2. Understanding these charges helps in predicting how ions will bond to form stable compounds.

• Positive ions, or cations, typically come from metals.
• Negative ions, or anions, often come from non-metals or polyatomic ions like sulfate.

Balancing these opposite charges is crucial to forming neutral compounds, which is often done by adjusting the number of ions used.

Sodium Sulfate

Sodium sulfate is a ternary ionic compound, meaning it consists of three elements: sodium, sulfur, and oxygen. Its chemical formula is \(\mathrm{Na}_{2} \mathrm{SO}_{4}\). This compound is made by combining sodium ions (\(\mathrm{Na}^+\)) with a sulfate ion (\(\mathrm{SO_{4}^{2-}}\)).
Each sodium ion has a +1 charge, so two sodium ions are needed to balance out the -2 charge of the sulfate ion.
Sodium sulfate is used in various industrial processes, such as detergents and in the paper industry. Understanding how sodium sulfate is structured helps students learn about compound formation and the role of ion charges in determining chemical formulas.

Sulfate and Sulfite Ions

Sulfate (\(\mathrm{SO_{4}^{2-}}\)) and sulfite (\(\mathrm{SO_{3}^{2-}}\)) ions are similar, yet distinct. Both are examples of polyatomic ions, which are groups of atoms covalently bonded that carry an overall charge.

• The sulfate ion has the formula \(\mathrm{SO_{4}^{2-}}\) and contains one sulfur atom bonded to four oxygen atoms, resulting in a -2 charge.
• The sulfite ion has the formula \(\mathrm{SO_{3}^{2-}}\) and consists of one sulfur atom bonded to three oxygen atoms, also carrying a -2 charge.

These ions differ by the number of oxygen atoms bonded to sulfur. The change in oxygen affects the properties and reactivity of the ions, which is important when predicting how these ions form compounds with metals like sodium or francium. When forming compounds, the ion charges must be balanced for the compound to be neutral, something critical to remember in chemistry problems.