A solution of sodium sulfate is combined with a solution of barium chloride. Does a precipitation reaction occur? If so, which salt precipitates?

Chemical equations are symbolic representations of chemical reactions, where the reactants are shown on the left and the products on the right. The equation is balanced when the number of atoms for each element is equal on both sides, adhering to the law of conservation of mass. For example, in our precipitation reaction, the balanced chemical equation is:
\[ \text{Na}_2\text{SO}_4 (aq) + \text{BaCl}_2 (aq) \rightarrow 2 \text{NaCl} (aq) + \text{BaSO}_4 (s) \]
This equation shows that sodium sulfate and barium chloride react to form sodium chloride and barium sulfate. The states of the compounds are indicated as (aq) for aqueous or dissolved in water, and (s) for solid, representing the precipitate formed in this reaction.

Solubility rules help predict the solubility of ionic compounds in water. These guidelines can be used to foresee if a substance will dissolve (forming an aqueous solution) or form a precipitate when two solutions are mixed. Certain ions almost always make soluble compounds, like sodium (Na⁺) and nitrate (NO₃⁻), whereas others often lead to precipitates, such as silver (Ag⁺) with chloride (Cl⁻).

In the reaction presented, sodium chloride (NaCl) is soluble, but barium sulfate (BaSO₄) is not, based on the solubility rules that state sulfates are insoluble with certain cations like barium (Ba²⁺). Recognizing these patterns is vital when predicting the outcome of a double displacement reaction and identifying precipitates.

Ionic compounds consist of positive and negative ions held together by strong electrostatic forces known as ionic bonds. In a solution, these compounds often dissociate into their respective ions. For instance, sodium sulfate, \( \text{Na}_2\text{SO}_4 \), will dissociate into two sodium ions, \( 2\text{Na}^+ \), and one sulfate ion, \( \text{SO}_4^{2−} \), when dissolved in water. Similarly, barium chloride, \( \text{BaCl}_2 \), dissociates into one barium ion, \( \text{Ba}^{2+} \), and two chloride ions, \( 2\text{Cl}^- \). The ability to predict the behavior of ionic compounds in solution is crucial in understanding precipitation reactions and other chemical processes.

Double displacement reactions, also known as metathesis, involve the exchange of ions between two compounds forming new compounds. These reactions can result in the formation of a gas, a weak or non-electrolyte, or, as in the exercise, an insoluble solid called a precipitate. When sodium sulfate reacts with barium chloride, their ions switch partners, leading to the formation of sodium chloride and barium sulfate. Since barium sulfate is insoluble in water, it precipitates out of the solution, visibly demonstrating the reaction. Understanding double displacement reactions is useful for predicting the products of chemical reactions involving ionic compounds that occur in aqueous solutions.