A beaker of nitric acid is neutralized with calcium hydroxide. Write a balanced molecular equation and a net ionic equation for this reaction.

A chemical reaction is a process where substances, known as reactants, transform into different substances called products. This transformation occurs through a rearrangement of atoms and can involve the breaking and forming of chemical bonds. In our example, we deal with a neutralization reaction, which is a type of chemical reaction where an acid and a base react to form water and a salt. Specifically, nitric acid (a strong acid) reacts with calcium hydroxide (a strong base) to produce water and calcium nitrate (a salt).

Understanding the nature of the reactants—acids and bases—in this context is essential. Acids are proton donors, meaning that they contribute hydrogen ions (H+) when dissolved in water, while bases are proton acceptors, providing hydroxide ions (OH-) in aqueous solutions. When these ions meet, they combine to form water, which is the essence of the neutralization process.

Balancing molecular equations is a fundamental skill in chemistry that ensures the law of conservation of mass is obeyed; the total mass of the reactants must equal the total mass of the products in a chemical reaction. To balance an equation, one adjusts the coefficients (the numbers in front of molecules) without altering the subscripts in the molecular formulas. The coefficients indicate the number of units of each substance involved in the reaction.

In the neutralization reaction between nitric acid and calcium hydroxide, the initial unbalanced equation is written based on the known reactants and products. Then, the equation is balanced by ensuring that the number of atoms of each element is the same on both sides. For instance, the reaction starts with two nitrate ions (\textbf{NO3}-) and one calcium ion (\textbf{Ca2+}) on the reactant side, hence you need two nitrate ions and one calcium ion on the product side, leading to the balanced molecular equation: \[ 2HNO3 + Ca(OH)2 \rightarrow 2H2O + Ca(NO3)2 \]. This step is crucial for correctly representing the reaction and for subsequent steps like writing the net ionic equation.

Spectator ions are ions present in a reaction mixture that do not participate directly in the chemical change occurring during the reaction. These ions do not undergo any chemical transformation and appear unchanged on both the reactant and product sides of the equation. Identifying these ions is essential when converting a total ionic equation into a net ionic equation, as the net ionic equation only includes the ions and molecules directly involved in the reaction.

In our example, the total ionic equation includes calcium ions (\textbf{Ca2+}(aq)) and nitrate ions (\textbf{NO3}- (aq)) that are spectators; they remain in the aqueous phase without modification. Removing these spectator ions from the total ionic equation leaves us with the pure essence of the reaction—the net ionic equation which simply shows the formation of water: \[ 2H+(aq) + 2OH-(aq) \rightarrow 2H2O(l) \]. This instructive distillation of the reaction underscores the actual change taking place: the neutralization of hydrogen ions by hydroxide ions to produce water.