Question

Determine which of the following react(s) with HCl(ag) to produce a gas, and write a net ionic equation(s) for the reaction(s). (a) \(\mathrm{Na}_{2} \mathrm{SO}_{4} ;\) (b) \(\mathrm{KHSO}_{3}\); (c) \(\mathrm{Zn}(\mathrm{OH})_{2};\) (d) \(\mathrm{CaCl}_{2}\).

Short answer

The substances that react with Hydrochloric Acid (HCl) to produce a gas are Potassium bisulfite (KHSO3). The ionic equation for the reaction is \(HSO3- + H^{+} \rightarrow SO2(g) + H2O\).

Step-by-step solution

Test Sodium sulfate (Na2SO4)

Sodium sulfate does not react with Hydrochloric acid to produce a gas. Sodium sulfate disassociates into Na+ and SO42-. Neither of these ions react with HCl to produce a gas.

Test Potassium bisulfite (KHSO3)

Potassium bisulfite reacts with Hydrochloric acid to produce a gas. The bisulfite ion (HSO3-) reacts with H+ to produce SO2, a gas, and water (H2O). The balanced ionic equation is \(HSO3- + H^{+} \rightarrow SO2(g) + H2O\).

Test Zinc Hydroxide (Zn(OH)2)

Zinc Hydroxide reacts with Hydrochloric acid to produce a gas. The hydroxide ion (OH-) reacts with H+ to produce water (H2O). Since there are 2 OH- in Zn(OH)2, the balanced ionic equation is \(2H^{+} + 2OH^{-} \rightarrow 2H2O(l)\). This is not considered a gas forming reaction since the product is in the liquid state. Hence, Zn(OH)2 does not produce a gas when reacted with HCl.

Test Calcium Chloride (CaCl2)

Calcium chloride does not react with Hydrochloric acid to produce a gas. Calcium chloride disassociates into Ca2+ and Cl-. Neither of these ions react with HCl to produce a gas.

Key concepts

Net Ionic Equations

In chemistry, understanding net ionic equations helps focus on the substances that truly change during a reaction. When writing net ionic equations, we omit the spectator ions, which are ions that do not participate in the chemical change. This simplification lets us see the core of the reaction.
The process starts with writing a balanced molecular equation. Then, break down all the aqueous compounds into their respective ions, unless they are weak electrolytes, gases, or solids. Finally, remove spectator ions and show only those that engage in forming new products.
In the exercise, take the example of Potassium bisulfite reacting with Hydrochloric acid. The bisulfite ion ( ext{HSO}_3^-) and the hydrogen ion ( ext{H}^+) are the key reactants. The net ionic equation is:

• \[\text{HSO}_3^- + \text{H}^+ \rightarrow \text{SO}_2(g) + \text{H}_2\text{O}\]

This shows the bisulfite ion transforming into sulfur dioxide gas and water, clearly spotlighting the chemical change.

Gas Production in Reactions

Certain chemical reactions produce gases as one of the products. These reactions are notable because gases are easily observed due to their bubble formation or odor. Recognizing if a reaction produces a gas can help predict how the reaction will behave both in a lab setting or in practical applications.
In the exercise we consider, Hydrogen Chloride (HCl) can produce gas when reacting with some compounds. For instance, Potassium bisulfite ( ext{KHSO}_3) undergoes a reaction with HCl, where the bisulfite ion ( ext{HSO}_3^-) reacts with hydrogen ions ( ext{H}^+) to create sulfur dioxide gas ( ext{SO}_2) and water. Observing this gas evolution can confirm the reaction was successful.
However, not all reactions with HCl lead to gas formation. For example, Sodium sulfate ( ext{Na}_2 ext{SO}_4) and Calcium chloride ( ext{CaCl}_2) do not produce gas when reacting with HCl, as there is no suitable chemical transformation to generate gas in these cases.

Acid-Base Reactions

Acid-base reactions, also known as neutralization reactions, take place when an acid and a base interact to produce water and sometimes a salt. These reactions are foundational in studying chemistry due to their prevalence and practical applications.
When Hydrochloric acid (HCl) reacts with bases, it can sometimes form gases, though the primary product is usually water. For example, when Zinc hydroxide ( ext{Zn}( ext{OH})_2) reacts with HCl, water is formed from the combination of ext{OH}^- ions and ext{H}^+ ions.

• \[2\text{H}^+ + 2\text{OH}^- \rightarrow 2\text{H}_2\text{O}(l)\]

While this is a typical neutralization with no gas formation, observing whether a new gaseous product was created is important to fully understand the nature of acid-base interactions.
Thus, identifying the characteristics in these reactions not only aids in solving chemical equations but also expands our knowledge on the subject of chemical interactions and their possible products.