Question

The permanganate anion has the formula \(\mathrm{MnO}_{4}^{-}\). Propose formulas and names for the ionic compounds between the permanganate ion and \(\mathrm{K}^{+}, \mathrm{Ca}^{2+},\) and \(\mathrm{Fe}^{3+}\).

Short answer

Potassium permanganate: \( \mathrm{KMnO}_{4} \), Calcium permanganate: \( \mathrm{Ca}(\mathrm{MnO}_{4})_{2} \), Iron(III) permanganate: \( \mathrm{Fe}(\mathrm{MnO}_{4})_{3} \).

Step-by-step solution

Identify the charge of permanganate ion

The permanganate ion is given as \( \mathrm{MnO}_{4}^{-} \). This means it carries a charge of \(-1\).

Combine permanganate ion with potassium ion

Since potassium ion \( \mathrm{K}^{+} \) has a charge of \(+1\), it can directly pair with permanganate ion to form a neutral compound. Thus, the formula is \( \mathrm{KMnO}_{4} \). The compound is named potassium permanganate.

Combine permanganate ion with calcium ion

Calcium ion \( \mathrm{Ca}^{2+} \) has a charge of \(+2\). To balance the charges, we need two permanganate ions. The formula becomes \( \mathrm{Ca}(\mathrm{MnO}_{4})_{2} \). The compound is named calcium permanganate.

Combine permanganate ion with iron ion

Iron ion \( \mathrm{Fe}^{3+} \) has a charge of \(+3\). To balance the charges, we need three permanganate ions. The formula becomes \( \mathrm{Fe}(\mathrm{MnO}_{4})_{3} \). The compound is named iron(III) permanganate.

Key concepts

Permanganate Ion

The permanganate ion is a type of polyatomic ion, which means it consists of more than one atom. Specifically, the chemical formula for the permanganate ion is \( \mathrm{MnO}_4^{-} \). It is made up of a manganese atom and four oxygen atoms, collectively carrying a negative one charge. This charge is important because it influences how the ion interacts with positively charged ions (cations) to form compounds.

• The manganese atom in \( \mathrm{MnO}_4^{-} \) is in a +7 oxidation state.
• Permanganate ions are commonly used in many chemical reactions as oxidizing agents due to their ability to accept electrons.

Understanding the role of the permanganate ion in ionic compounds helps in predicting the formulas and names of the resulting compounds when it combines with different cations.

Chemical Formulas

Chemical formulas represent the composition of a compound by demonstrating the types and numbers of atoms involved. For ionic compounds, like those formed by the permanganate ion, the formula must show the ions in the simplest ratio that results in a neutral compound.

• The formula for potassium permanganate, \( \mathrm{KMnO}_4 \), directly combines one potassium ion \( \mathrm{K}^{+} \) with one permanganate ion \( \mathrm{MnO}_4^{-} \).
• In calcium permanganate, \( \mathrm{Ca} (\mathrm{MnO}_4)_2 \), one calcium ion \( \mathrm{Ca}^{2+} \) pairs with two permanganate ions to balance the charges.
• For iron(III) permanganate, \( \mathrm{Fe} (\mathrm{MnO}_4)_3 \), one iron ion \( \mathrm{Fe}^{3+} \) pairs with three permanganate ions.

The process of creating chemical formulas from ions ensures the stability of the compounds by achieving charge balance, leading us to our next important concept.

Charge Balance

Charge balance is a crucial principle in the formation of ionic compounds. The overall charge of any ionic compound must equal zero. This means that the positive charges from the cations must perfectly offset the negative charges from the anions.

• In potassium permanganate, the single \( \mathrm{K}^{+} \) ion and \( \mathrm{MnO}_4^{-} \) ion naturally offset each other's charge, resulting in a neutral compound.
• In calcium permanganate, the \( +2 \) charge of the \( \mathrm{Ca}^{2+} \) ion is balanced by two \( \mathrm{MnO}_4^{-} \) ions, each with a \(-1\) charge, achieving neutrality.
• For iron(III) permanganate, the \( +3 \) charge of the \( \mathrm{Fe}^{3+} \) ion requires three \( \mathrm{MnO}_4^{-} \) ions to balance it out.

Understanding charge balance is key to writing correct chemical formulas and is a fundamental aspect of ionic compound formation. It ensures the compound is stable and adheres to the rules of chemistry by being electrically neutral.