Question

Calcium carbonate is another salt. Write its chemical formula. Would you expect calcium carbonate to be soluble or insoluble in water?

Short answer

The formula for calcium carbonate is CaCO₃, and it is insoluble in water.

Step-by-step solution

Identify the elements and their charges

Calcium carbonate is made up of calcium (Ca) and carbonate (CO₃). Calcium, in group 2 of the periodic table, forms a extsuperscript{2+} cation. Carbonate is a polyatomic ion with a charge of extsuperscript{2-}.

Write the chemical formula using charges

To write the chemical formula, balance the charges. Calcium has a charge of extsuperscript{2+} and carbonate has a charge of extsuperscript{2-}. The charges cancel each other, so the formula is CaCO₃.

Determine solubility in water

Generally, carbonates are insoluble in water except those of group 1 elements and ammonium. Since calcium is a group 2 element (alkaline earth metal), calcium carbonate (CaCO₃) is expected to be insoluble in water.

Key concepts

Chemical Formula

The chemical formula of a compound is a way of expressing information about the atoms that constitute the compound. It shows which types of atoms make up the molecule and how many of each type there are.

Calcium carbonate is composed of two main components: calcium (Ca) and carbonate (CO₃). The charge of calcium, which belongs to group 2 of the periodic table, is 2+. This indicates that calcium tends to lose two electrons to become stable. On the other hand, carbonate is a polyatomic ion carrying a charge of 2-.

To arrive at the correct chemical formula for calcium carbonate, we balance the charges from calcium and carbonate. A 2+ charge from calcium and a 2- charge from carbonate neutralize each other, resulting in the chemical formula: CaCO₃. This formula indicates one calcium atom combines with one carbonate grouping to form calcium carbonate.

Solubility

Solubility refers to the capacity of a substance to dissolve in a solvent, like water, to form a homogenous solution. In the case of calcium carbonate, its solubility in water can be predicted by applying general solubility rules.

Many carbonate salts are generally insoluble in water, with limited exceptions like those involving group 1 elements (like sodium and potassium) and ammonium ions. Since calcium belongs to group 2, the alkaline earth metals, calcium carbonate remains largely insoluble in water.

In practical terms, this means that when calcium carbonate is mixed with water, it remains mostly undissolved, settling at the bottom rather than forming a clear solution. This characteristic plays an important role in natural processes like the formation of caves and hard water, as well as in industrial applications such as water treatment and the production of lime.

Ionic Compounds

Ionic compounds are composed of positively and negatively charged ions that are held together by strong electrostatic forces known as ionic bonds. These compounds form when metals transfer electrons to nonmetals, resulting in a balanced charge, like the 2+ charge of calcium and the 2- charge of the carbonate ion.

Calcium carbonate exemplifies an ionic compound with its distinct crystal lattice structure. This structure forms because ions arrange themselves in a regular pattern to maximize attraction and minimize repulsion.

One of the distinguishing features of ionic compounds is their high melting and boiling points due to the strong ionic bonds. They also conduct electricity when molten or dissolved in water, although in the case of calcium carbonate, its solubility limits this conductive behavior. The ionic nature of calcium carbonate and similar compounds makes them crucial in many scientific and industrial processes.

Polyatomic Ions

Polyatomic ions are ions that consist of several atoms bonded together, behaving as a single unit with a net charge. Unlike simple ions that comprise single elements, polyatomic ions include multiple atoms.

Take the carbonate ion CO₃ 2- for instance. It consists of one carbon atom covalently bonded to three oxygen atoms, and together they possess a 2- charge. This negative charge results from excess electrons shared among the atoms, creating an overall charged species.

Polyatomic ions like carbonate often participate in forming ionic compounds. Calcium carbonate is a perfect example, where the polyatomic carbonate ion combines with the calcium ion to form an ionic lattice. Understanding polyatomic ions is vital for grasping various chemical reactions and compounds since they often appear in nature, industry, and biological systems.