Problem 15 - Chemistry: An Atoms-Focused Approach

Question

Identify the acids and bases in the following reactions: a. \(\mathrm{HCl}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell)\) b. \(\mathrm{MgCO}_{3}(s)+2 \mathrm{HCl}(a q) \rightarrow\) \(\mathrm{MgCl}_{2}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell)\) c. \(2 \mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)\)

Step-by-Step Solution

Answer

Question: Identify the acids and bases in the following three chemical reactions: a) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) b) MgCO3(s) + 2 HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l) c) 2 NH3(aq) + H2SO4(aq) → (NH4)2SO4(aq) Answer: a) Acid: HCl, Base: NaOH b) Acid: HCl, Base: MgCO3 c) Acid: H2SO4, Base: NH3

Step 1: Reaction a: Identifying acid and base

In the reaction \(\mathrm{HCl}(a q)+\mathrm{NaOH}(a q) \rightarrow \mathrm{NaCl}(a q)+\mathrm{H}_{2} \mathrm{O}(\ell)\), we can identify that HCl donates a proton (H+) and NaOH accepts a proton (H+). Therefore, HCl is the acid in this reaction, and NaOH is the base.

Step 2: Reaction b: Identifying acid and base

In the reaction \(\mathrm{MgCO}_{3}(s)+2 \mathrm{HCl}(a q) \rightarrow \mathrm{MgCl}_{2}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(\ell)\), we can identify that HCl donates a proton (H+) and MgCO3 accepts a proton (H+). Therefore, HCl is the acid in this reaction, and MgCO3 is the base.

Step 3: Reaction c: Identifying acid and base

In the reaction \(2 \mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}(a q)\), we can identify that H2SO4 donates two protons (2 H+) and NH3 accepts two protons (2 H+). Therefore, H2SO4 is the acid in this reaction, and NH3 is the base.

Key Concepts

Proton Donors

In acid-base chemistry, a proton donor is a substance that releases a proton, or hydrogen ion (\(H^+\)), during a reaction. Acids are typical proton donors. For instance, in the reactions examined, hydrochloric acid (\(HCl\)) donates a proton in reactions (a) and (b). Similarly, sulfuric acid (\(H_2SO_4\)) acts as a proton donor in reaction (c). When an acid donates a proton, it often forms a conjugate base. For example:

• When \(HCl\) donates a proton, it forms \(Cl^-\) as its conjugate base.
• For \(H_2SO_4\), losing a proton results in \(HSO_4^-\). \(HSO_4^-\) can give up another proton to form \(SO_4^{2-}\) in a subsequent reaction.

Proton donors are crucial for many chemical reactions and play a vital role in processes like digestion and industrial synthesis of compounds. Understanding proton donation helps explain the nature of many biological and chemical systems.

Proton Acceptors

Proton acceptors are substances that gain a proton (\(H^+\)) during a chemical reaction. These are often base substances. For example, in the reactions provided, sodium hydroxide (\(NaOH\)) accepts a proton from \(HCl\), turning into water (\(H_2O\)) in reaction (a). In response (c), ammonia (\(NH_3\)) accepts protons from sulfuric acid to form ammonium sulfate (\((NH_4)_2SO_4\)).The role of proton acceptors is crucial for neutralizing acids in reactions, leading to the formation of water and salt.

• In reaction (b), magnesium carbonate (\(MgCO_3\)) acts as the base, accepting protons to facilitate the breakdown into water and carbon dioxide.
• Learning to identify bases in reactions enhances comprehension of processes such as neutralization and buffer systems, which stabilize pH in biological environments.

This concept not only simplifies the understanding of reactions but also applies to everyday processes, such as antacid use in neutralizing stomach acid.

Neutralization Reactions

Neutralization occurs when an acid and a base react to form water and a salt, often resulting in a solution that is neither acidic nor basic. This concept is exemplified in the given reactions. Consider reaction (a) of \(HCl\) and \(NaOH\). HCl donates a proton to \(NaOH\), resulting in the creation of water and sodium chloride (\(NaCl\)), which is an example of a neutralization reaction.Neutralization is not only fundamental in laboratory settings but also in real-life applications:

• In reaction (b), \(MgCO_3\) neutralizes the acid \(HCl\), forming magnesium chloride (\(MgCl_2\)), carbon dioxide (\(CO_2\)), and water (\(H_2O\)), each playing a part in this complete reaction.
• For reaction (c), ammonia (\(NH_3\)) reacts with \(H_2SO_4\), where the neutralization results in ammonium sulfate (\((NH_4)_2SO_4\)).

Grasping this process aids in the understanding of solutions and reactions that require pH adjustment, such as in wastewater treatment or agriculture. Neutralization is integral to maintaining homeostasis in various environmental and biological systems.