Question

Provide the formula for each of the following ternary ionic compounds: (a) cuprous chlorite (b) plumbic sulfite (c) mercuric chlorate (d) ferrous chromate

Short answer

(a) CuClO₂, (b) Pb(SO₃)₂, (c) Hg(ClO₃)₂, (d) FeCrO₄.

Step-by-step solution

Identify the Ions

Start by identifying both the cation and the anion in each compound. In a ternary ionic compound, the cation comes first, followed by the polyatomic anion. (a) Cuprous (copper(I), Cu⁺) and chlorite (ClO₂⁻) (b) Plumbic (lead(IV), Pb⁴⁺) and sulfite (SO₃²⁻) (c) Mercuric (mercury(II), Hg²⁺) and chlorate (ClO₃⁻) (d) Ferrous (iron(II), Fe²⁺) and chromate (CrO₄²⁻).

Combine the Ions to Form Neutral Compounds

Combine the ions to form a neutral compound by ensuring that the total positive charge equals the total negative charge. Use subscripts to balance the charges. (a) Cu⁺ (cation) and ClO₂⁻ (anion) yield the formula CuClO₂. (b) Pb⁴⁺ and SO₃²⁻: The least common multiple of 4 and 2 is 4, so you need two SO₃²⁻ ions to balance one Pb⁴⁺, resulting in Pb(SO₃)₂. (c) Hg²⁺ and ClO₃⁻: You need two ClO₃⁻ ions to balance one Hg²⁺, leading to Hg(ClO₃)₂. (d) Fe²⁺ and CrO₄²⁻ combine in a 1:1 ratio to form FeCrO₄.

Write the Formulas

Write each compound's formula based on the balanced ionic charges. (a) The formula for cuprous chlorite is CuClO₂. (b) The formula for plumbic sulfite is Pb(SO₃)₂. (c) The formula for mercuric chlorate is Hg(ClO₃)₂. (d) The formula for ferrous chromate is FeCrO₄.

Key concepts

Understanding Polyatomic Ions

Polyatomic ions are more than just single ions; they are groups of two or more atoms that are covalently bonded together but carry an overall charge due to the loss or gain of electrons. These ions act as a unit in chemical reactions and are commonly found in ternary ionic compounds, where they pair with a metal ion. Recognizing them is crucial for writing chemical formulas.

• Common Polyatomic Ions: Some of the frequently encountered polyatomic ions include: sulfate (SO₄²⁻), nitrate (NO₃⁻), and ammonium (NH₄⁺).
• Structure: Each polyatomic ion has a specific composition of atoms and an associated charge, which must be learned to use them accurately in chemical formulas.
• Examples from Exercises:
• Chlorite, ClO₂⁻, seen in cuprous chlorite, has one chlorine atom and two oxygen atoms.
• Chromate, CrO₄²⁻, present in ferrous chromate, consists of one chromium atom and four oxygen atoms.

Remembering the names, formulas, and charges of these ions will significantly aid in the construction of accurate chemical equations.

Formulating Chemical Formulas

Writing chemical formulas for ternary ionic compounds involves identifying the cation, usually a metal ion, and the anion, often a polyatomic ion. The goal is to ensure that the resulting compound is electrically neutral, meaning the total positive charges and the total negative charges must balance.

Steps to Write Chemical Formulas:

• Identify ions: Determine the charges and the composition of both the cation and an anion. For instance, in mercuric chlorate, Hg²⁺ represents the cation and ClO₃⁻ represents the anion.
• Balance charges: Use subscripts in the formula to adjust the ratio of ions so that their charges balance. In the same example, two ClO₃⁻ ions are needed to balance one Hg²⁺, leading to the formula Hg(ClO₃)₂.
• Formula writing: Properly position each ion with correct subscripts. If multiple polyatomic ions are required to balance the charge, enclose their formula in parentheses. This method is employed in compounds like Pb(SO₃)₂.

Using these methods will lead to the correct structure of chemical formulas for ternary ionic compounds.

Balancing Charges in Ionic Compounds

For a ternary ionic compound to be neutral, the total positive and negative charges must cancel each other out. This is where balancing charges becomes essential. Achieving neutral charge ensures the stability of the compound and maintains its structural integrity in chemical reactions.

Key Principles:

• Charge recognition: Each ion has a specific charge, like +1 or -2, that must be considered when pairing ions in compound formulations. Cu⁺ and ClO₂⁻, for example, naturally balance each other's charges, forming CuClO₂.
• Using subscripts: Subscripts in chemical formulas indicate how many of each ion are needed. If an ion’s charge isn't enough to balance another ion's charge, add more of one to achieve neutrality. For example, Pb⁴⁺ requires two sulfite ions (SO₃²⁻), giving us Pb(SO₃)₂.
• Least Common Multiple (LCM) approach: Apply LCM to determine the smallest number of ions to achieve equal charge. For ions with charges such as +4 and -2, as in plumbic sulfite, the LCM is 4. Thus, you need two -2 ions to pair with one +4.

This careful balancing ensures the chemical stability of the ionic compound and is a core skill in chemistry.