Iron(III) sulfate \(\left[\mathrm{Fe}_{2}\left(\mathrm{SO}_{4}\right)_{3}\right]\) is composed of \(\mathrm{Fe}^{3+}\) and \(\mathrm{SO}_{4}^{2-}\) ions. Explain why a sample of iron(III) sulfate is uncharged.

Ionic compounds are substances made up of positively charged ions, called cations, and negatively charged ions, called anions. These ions are held together by strong electrostatic forces of attraction, known as ionic bonds. The most straightforward examples are found among the alkali metals and the halogens. For instance, sodium (Na), a typical alkali metal, loses an electron to become Na+, while chlorine (Cl), a common halogen, gains an electron to become Cl-. When these two ions combine, they form sodium chloride (NaCl), a neutral ionic compound.
Ionic compounds have distinctive properties, such as high melting and boiling points due to the strong attractions between the ions. They are also typically solid at room temperature and can conduct electricity when melted or dissolved in water because their ions are free to move about as carriers of electric current. Understanding these properties helps in explaining why substances like iron(III) sulfate are solid, high melting, and capable of conducting electricity when dissolved.

Chemical formulas represent the composition of a substance using element symbols and numerical subscripts. For ionic compounds like iron(III) sulfate, the formula provides not only the ratio of ions but also conveys significant information about the nature of the bond and the structure of the compound. Iron(III) sulfate's formula, Fe2(SO4)3, shows that each formula unit consists of two atoms of iron (Fe) and three sulfate ions (SO₄).

Understanding Subscripts and Charges

In this formula, the subscript '2' after iron indicates that there are two Fe³⁺ ions. Similarly, the subscript '3' after the sulfate group indicates that three sulfate (SO₄)^2- ions are present. These subscripts are crucial because they reflect the actual ratio of ions required to maintain charge neutrality in the compound. The chemical formula provides a blueprint for constructing a compound from its constituent ions and is an essential concept for students grasping the composition of ionic substances.

Charge neutrality is the principle that the total charge within an ionic compound must equal zero. This means the sum of the positive charges of the cations must be balanced by an equivalent total negative charge from the anions. In our example of iron(III) sulfate, we have iron ions with a +3 charge (Fe³⁺) and sulfate ions with a -2 charge (SO₄)^2-.
From the chemical formula, Fe2(SO4)3, we know there are two iron(III) ions and three sulfate ions. The total positive charge is 2 × +3 = +6, and the total negative charge is 3 × -2 = -6. When these charges are combined, the sum is zero, which demonstrates charge neutrality. This concept is fundamental in explaining why a sample of iron(III) sulfate does not carry an overall charge due to the equal and opposite charges of the ions balancing each other.

Importance in Chemical Reactions

Charge neutrality must be maintained during chemical reactions. This is why, when chemicals react, ions may swap partners, but the overall charge should remain balanced. Understanding this concept is critical for students who are learning how to predict the products of chemical reactions and the accurate stoichiometry involved.