Question

Complete and balance each acid-base equation. a. \(\operatorname{HI}(a q)+\operatorname{LiOH}(a q) \longrightarrow\) b. \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(a q) \rightarrow\) c. \(\mathrm{HCl}(a q)+\mathrm{Ba}(\mathrm{OH})_{2}(a q) \stackrel{(a q)}{\longrightarrow}\)

Short answer

[\(\operatorname{HI}(aq) + \operatorname{LiOH}(aq) \longrightarrow H_2O(l) + \operatorname{LiI}(aq)\), \(2\mathrm{HC}_{2}\mathrm{H}_{3}\mathrm{O}_{2}(aq) + \mathrm{Ca}(\mathrm{OH})_{2}(aq) \rightarrow 2 H_2O(l) + \mathrm{Ca}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2(aq)\), \(2\mathrm{HCl}(aq) + \mathrm{Ba}(\mathrm{OH})_{2}(aq) \rightarrow 2 H_2O(l) + \mathrm{BaCl}_2(aq)\)]

Step-by-step solution

Identifying the Products of the Acid-Base Reaction (a)

The reaction involves a strong acid (HI) reacting with a strong base (LiOH). The products of such an acid-base reaction are typically water (H2O) and a salt. In this case, the salt is lithium iodide (LiI). The balanced chemical equation is: \[\operatorname{HI}(aq) + \operatorname{LiOH}(aq) \longrightarrow H_2O(l) + \operatorname{LiI}(aq)\]

Balancing the Equation (a)

Both the acid and the base are monoprotic (each has one hydrogen ion to donate/accept), and thus the equation is already balanced as written with a 1:1 ratio. No further changes are needed.

Identifying the Products of the Acid-Base Reaction (b)

Here, a weak acid (acetic acid, HC2H3O2) reacts with a strong base (calcium hydroxide, Ca(OH)2). The products are water and a salt. In this case, the salt is calcium acetate (Ca(C2H3O2)2). The balanced chemical equation is: \[\mathrm{HC}_{2}\mathrm{H}_{3}\mathrm{O}_{2}(aq) + \mathrm{Ca}(\mathrm{OH})_{2}(aq) \rightarrow 2 H_2O(l) + \mathrm{Ca}(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2)_2(aq)\]

Balancing the Equation (b)

Calcium hydroxide is diprotic (has two hydroxide ions), which means two moles of acetic acid will react with one mole of calcium hydroxide to produce the salt and water. The equation requires a 2:1 ratio of acetic acid to calcium hydroxide to balance the hydrogen and hydroxide ions.

Identifying the Products of the Acid-Base Reaction (c)

The reaction involves a strong acid (HCl) and a strong base (Ba(OH)2). The products are water and a salt. In this case, the salt is barium chloride (BaCl2). The balanced chemical equation is: \[\mathrm{HCl}(aq) + \mathrm{Ba}(\mathrm{OH})_{2}(aq) \rightarrow 2 H_2O(l) + \mathrm{BaCl}_2(aq)\]

Balancing the Equation (c)

Barium hydroxide is diprotic, needing two moles of HCl for every mole of Ba(OH)2 to balance the reaction. Hence, we put a coefficient of 2 in front of HCl to yield two moles of water and one mole of barium chloride.

Key concepts

Balancing Chemical Equations

Understanding how to balance chemical equations is crucial for students to grasp the concept of conservation of matter. The principle behind balancing chemical equations hinges on the fact that the number of atoms of each element must be the same on both the reactant and product sides of the equation. In acid-base reactions, this often involves making sure that the number of hydrogen ions (H⁺) from the acid matches the number of hydroxide ions (OH^-) from the base.

For example, consider the reaction between hydroiodic acid (HI) and lithium hydroxide (LiOH). Since both HI and LiOH are monoprotic, meaning they can each donate or accept one H⁺, they will combine in a 1:1 ratio to form lithium iodide (LiI) and water (H₂O), keeping the equation balanced as seen in the exercise provided. This kind of stoichiometry is fundamental and always the first check-point in ensuring the formula is correctly balanced.

Strong and Weak Acids and Bases

The strength of an acid or a base is determined by its ability to dissociate in water. Strong acids and bases dissociate completely, while weak acids and bases partially dissociate. A strong acid, like hydrochloric acid (HCl), will completely ionize in solution to produce a high concentration of H⁺ ions. Meanwhile, a weak acid such as acetic acid (HC₂H₃O₂) will not fully ionize, resulting in a lower concentration of H⁺ ions.

Similarly, strong bases, like barium hydroxide (Ba(OH)₂), dissociate completely to yield OH^- ions, while weak bases partially dissociate. It's important to understand these concepts because the strength of the acid or base can affect the ratio of reactants in the acid-base neutralization reaction, as we have seen in the step-by-step solutions, where a weak acid reacts with a strong base in a different stoichiometric ratio than when strong acids react with strong bases.

Acid-Base Neutralization

Acid-base neutralization is a type of chemical reaction where an acid and a base react to form water and a salt. This process is fundamental to understanding various chemical processes and real-world applications, such as titrations in laboratory settings and the buffering systems in the human body.

In each of the examples provided, the acid and base react to neutralize each other's properties, resulting in a salt and water. The salt is typically composed of the cation from the base and the anion from the acid. When the reaction involves a monoprotic acid and a monoprotic base, the reaction will result in a one to one ratio of acid to base. However, if one of the reactants is diprotic, as seen with calcium hydroxide (Ca(OH)₂), the stoichiometry will adjust accordingly to ensure that all of the hydroxide ions are neutralized, resulting in a different ratio. It's these subtle nuances in acid-base neutralization reactions that can present challenges, and understanding them is essential for mastering the topic.