Question

What strong acid and what strong base would react in aqueous solution to produce the following salts? a. potassium perchlorate, ${\mathrm{KClO}}_4$ b. cesium nitrate, ${\mathrm{CSNO}}_3$ c. potassium chloride, KCl d. sodium sulfate, ${\mathrm{Na}}_2{\mathrm{SO}}_4$

Short answer

a. Perchloric acid (HClO4) and potassium hydroxide (KOH) b. Nitric acid (HNO3) and cesium hydroxide (CsOH) c. Hydrochloric acid (HCl) and potassium hydroxide (KOH) d. Sulfuric acid (H2SO4) and sodium hydroxide (NaOH)

Step-by-step solution

a. potassium perchlorate, ${\mathrm{KClO}}_4$

Step 1: Identify the ions For potassium perchlorate, we have a potassium ion (K+) and a perchlorate ion (ClO4-). Step 2: Pair ions with corresponding acid or base For K+, its corresponding strong base would be potassium hydroxide (KOH). For ClO4-, its corresponding strong acid would be perchloric acid (HClO4). Thus, the strong acid and strong base that would react in aqueous solution to produce potassium perchlorate are perchloric acid (HClO4) and potassium hydroxide (KOH).

b. cesium nitrate, ${\mathrm{CsNO}}_3$

Step 1: Identify the ions For cesium nitrate, we have a cesium ion (Cs+) and a nitrate ion (NO3-). Step 2: Pair ions with corresponding acid or base For Cs+, its corresponding strong base would be cesium hydroxide (CsOH). For NO3-, its corresponding strong acid would be nitric acid (HNO3). Thus, the strong acid and strong base that would react in aqueous solution to produce cesium nitrate are nitric acid (HNO3) and cesium hydroxide (CsOH).

c. potassium chloride, KCl

Step 1: Identify the ions For potassium chloride, we have a potassium ion (K+) and a chloride ion (Cl-). Step 2: Pair ions with corresponding acid or base For K+, its corresponding strong base would be potassium hydroxide (KOH). For Cl-, its corresponding strong acid would be hydrochloric acid (HCl). Thus, the strong acid and strong base that would react in aqueous solution to produce potassium chloride are hydrochloric acid (HCl) and potassium hydroxide (KOH).

d. sodium sulfate, ${\mathrm{Na}}_2{\mathrm{SO}}_4$

Step 1: Identify the ions For sodium sulfate, we have two sodium ions (Na+), and a sulfate ion (SO4^2-). Step 2: Pair ions with corresponding acid or base For Na+, its corresponding strong base would be sodium hydroxide (NaOH). For SO4^2-, its corresponding strong acid would be sulfuric acid (H2SO4). Thus, the strong acid and strong base that would react in aqueous solution to produce sodium sulfate are sulfuric acid (H2SO4) and sodium hydroxide (NaOH).

Key concepts

Chemical Equilibrium

Understanding chemical equilibrium is vital for students studying acid-base reactions.
Chemical equilibrium occurs when a chemical reaction and its reverse reaction proceed at the same rate, leading to a balance where the concentrations of reactants and products remain constant over time. This balance is dynamic, meaning that reactions are still occurring, but with no net change in the amounts of substances. In the context of acid-base reactions, when a strong acid and a strong base react, they do so completely to form the products, usually with no reactants left, reaching what is known as stoichiometric equilibrium.

This is particularly relevant when discussing strong acids and bases, which dissociate fully in water, leaving no unreacted species — a concept that challenges the typical notion of equilibrium where both reactants and products are present. It's critical for students to grasp that strong acid-base reactions reach completion and are not typically concerned with the equilibrium constants that describe the balance of less reactive, reversible reactions.

Strong Acids and Bases

Delving into the nature of strong acids and bases can offer substantial insights into their behavior in aqueous solutions. Strong acids, such as hydrochloric acid (HCl) and sulfuric acid (H2SO4), ionize completely in water to produce a high concentration of hydrogen ions (H+), leading to a low pH. Similarly, strong bases, like sodium hydroxide (NaOH) and potassium hydroxide (KOH), dissociate fully to yield hydroxide ions (OH-) and result in a high pH.

Students should note that, because of their complete ionization, strong acids and bases do not retain their original molecular form in solution and are always represented in ionized form when writing chemical equations. This total dissociation is pivotal for understanding their reactions, as it guarantees that when a strong acid and base react, they will exclusively form water and a salt, with no remaining acid or base.

Aqueous Solution Chemistry

When discussing acid-base reactions, one must not overlook the significance of aqueous solution chemistry.
An aqueous solution is one where water is the solvent that dissolves the solute, which could be acids like nitric acid (HNO3), or bases like cesium hydroxide (CsOH). The solubility and ionic dissociation in an aqueous solution are key factors that decide the outcome of a chemical reaction. For strong acids and bases, this environment provides the medium for complete dissociation into ions.

Importantly, in aqueous solutions, water can also act as both an acid and a base – a property known as amphotericity. This feature can influence the pH of the solution and the direction of acid-base reactions. Students should recognize that in water, the ionization of strong acids and bases is a critical step that leads to the neutralization and the formation of salts, which then dissolve or precipitate depending on their solubility in water.

Neutralization Reactions

Neutralization reactions are arguably the crux of understanding acid-base interactions in aqueous solutions.
A neutralization reaction is where an acid and a base react to form water and a salt. In the cases provided in the exercise, such as the reaction to produce potassium chloride (KCl) from hydrochloric acid (HCl) and potassium hydroxide (KOH), the hydrogen ions (H+) from the acid and the hydroxide ions (OH-) from the base combine to create water (H2O), while the remaining ions form the salt. It's a beautiful illustration of acid-base chemistry's most fundamental premise: the exchange of ions.

When teaching this concept, it is essential to emphasize the stoichiometry of the reaction. The mole ratio between the acid and the base must be exact for complete neutralization. Any deviation may result in an acidic or basic solution, which would not be neutral. This exercise can be an excellent practical application of stoichiometry in neutralization reactions and can reinforce a student's understanding of the equivalence point — where the number of moles of hydrogen ions equals the number of moles of hydroxide ions.