Question

Write the chemical formula for the following ternary compounds given their constituent ions: (a) potassium nitrate, \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\) (b) ammonium dichromate, \(\mathrm{NH}_{4}{ }^{+}\) and \(\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}\) (c) aluminum sulfite, \(\mathrm{Al}^{3+}\) and \(\mathrm{SO}_{3}^{2-}\) (d) chromium(III) hypochlorite, \(\mathrm{Cr}^{3+}\) and \(\mathrm{ClO}^{-}\)

Short answer

(a) \(\mathrm{KNO}_{3}\); (b) \((\mathrm{NH}_{4})_{2}\mathrm{Cr}_{2}\mathrm{O}_{7}\); (c) \(\mathrm{Al}_{2}(\mathrm{SO}_{3})_{3}\); (d) \(\mathrm{Cr}(\mathrm{ClO})_{3}\).

Step-by-step solution

Understanding Ternary Compounds

Ternary compounds are composed of three different elements, typically consisting of a metal cation and a polyatomic anion. When writing the chemical formula, the charges of the ions must balance to create a neutral compound.

Writing the Formula for Potassium Nitrate

Potassium nitrate is formed from potassium ions, \(\mathrm{K}^{+}\), and nitrate ions, \(\mathrm{NO}_{3}^{-}\). Since both ions have equal but opposite charges (+1 for \(\mathrm{K}^{+}\) and -1 for \(\mathrm{NO}_{3}^{-}\)), the formula for potassium nitrate is \(\mathrm{KNO}_{3}\).

Writing the Formula for Ammonium Dichromate

Ammonium dichromate is formed from ammonium ions, \(\mathrm{NH}_{4}^{+}\), and dichromate ions, \(\mathrm{Cr}_{2}\mathrm{O}_{7}^{2-}\). We need two ammonium ions to balance the charge of one dichromate ion. The formula is \((\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2}\mathrm{O}_{7}\).

Writing the Formula for Aluminum Sulfite

Aluminum sulfite is formed from aluminum ions, \(\mathrm{Al}^{3+}\), and sulfite ions, \(\mathrm{SO}_{3}^{2-}\). To balance the charges, we need two aluminum ions and three sulfite ions. The formula is \(\mathrm{Al}_{2}(\mathrm{SO}_{3})_{3}\).

Writing the Formula for Chromium(III) Hypochlorite

Chromium(III) hypochlorite is formed from chromium(III) ions, \(\mathrm{Cr}^{3+}\), and hypochlorite ions, \(\mathrm{ClO}^{-}\). Three hypochlorite ions are required to balance the charge of one chromium(III) ion. Therefore, the formula is \(\mathrm{Cr}(\mathrm{ClO})_{3}\).

Key concepts

Ternary Compounds

Ternary compounds are fascinating chemical compounds formed by three elements. These can often be recognized because they contain a metal, a non-metal, and typically a polyatomic ion.
The formation of a ternary compound results from the union of these three different kinds of atoms.
Examples include potassium nitrate \( \mathrm{KNO}_{3} \) and ammonium dichromate \((\mathrm{NH}_{4})_{2} \mathrm{Cr}_{2}\mathrm{O}_{7}\). Key points about ternary compounds:

• They consist of three different elements.
• Contain a metal cation and a polyatomic anion.
• The charges of these ions must balance to form a neutral compound.

To figure out their chemical formula, it is crucial to understand the particular ions involved and their charges.

Ion Charges

Ion charges are essential to predict how elements combine to form compounds. An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
For instance,

• Positive ions (cations) such as \( \mathrm{K}^{+}, \mathrm{NH}_{4}^{+}, \mathrm{Al}^{3+} \)
• Negative ions (anions) like \( \mathrm{NO}_{3}^{-}, \mathrm{Cr}_{2}\mathrm{O}_{7}^{2-}, \mathrm{SO}_{3}^{2-}, \mathrm{ClO}^{-} \)

For a compound to be stable and neutral, the total positive charge must balance the total negative charge. This balance dictates the ratio of ions required in a chemical formula.

Polyatomic Ions

Polyatomic ions, as the name suggests, are ions composed of more than one atom.
These ions act as a single charged entity.
Understanding their charge is crucial for balancing chemical formulas in compounds.Some common polyatomic ions include:

• Nitrate \( \mathrm{NO}_{3}^{-} \)
• Dichromate \( \mathrm{Cr}_{2}\mathrm{O}_{7}^{2-} \)
• Sulfite \( \mathrm{SO}_{3}^{2-} \)
• Hypochlorite \( \mathrm{ClO}^{-} \)

When writing chemical formulas, it is essential to recognize these ions and their consistent charge patterns, as they significantly affect the stoichiometry of compounds.

Neutral Compound

A neutral compound is the fundamental aim when writing chemical formulas. This neutrality means that the sum of positive and negative charges in the compound is zero.
For instance, when creating potassium nitrate, the potassium ion \( \mathrm{K}^{+} \) and nitrate ion \( \mathrm{NO}_{3}^{-} \) must cancel each other out resulting in \( \mathrm{KNO}_{3} \).
Steps to achieve neutrality:

• Identify the cations and anions involved.
• Use their charges to determine the ratio required to neutralize the compound.
• Write out the formula combining the ions in the appropriate proportions.

Following these steps ensures that the resulting compound is electrically neutral, making it more stable and valid.

Balancing Chemical Equations

Balancing chemical equations is a fundamental concept in chemistry that ensures the law of conservation of mass is fulfilled.
This concept often interconnects with creating neutral compounds because it involves ensuring each kind of atom is accounted for similarly on both sides of the equation. In ternary compounds:

• Start by writing down all reactants and products.
• Count the number of each type of ion or atom involved.
• Adjust coefficients to ensure the number of each type of ion is the same on both sides of the equation.

Balancing equations carefully ensures accurately represented chemical reactions, vital for predicting how substances will react under different conditions.