Problem 48 - Chemistry The Science in Context

Question

When \(1,\) 2-diaminoethane, \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2},\) dissolves in water, the resulting solution is basic. Write the formula of the ionic compound that is formed when hydrochloric acid is added to a solution of 1,2 -diaminoethane.

Step-by-Step Solution

Answer

Answer: The formula of the ionic compound formed is H₂NCH₂CH₂NH₃Cl.

Step 1: Reaction between 1,2-diaminoethane and water

Write down the chemical equations for 1,2-diaminoethane reacting with water: H₂NCH₂CH₂NH₂ (aq) + H₂O (l) ↔ H₂NCH₂CH₂NH₃⁺ (aq) + OH⁻ (aq) The 1,2-diaminoethane picks up a proton (H⁺) from water, producing a hydroxide ion (OH⁻)

Step 2: Identify the basic ion

The basic ion that is formed in the solution of 1,2-diaminoethane is the hydroxide ion (OH⁻)

Step 3: Reaction between basic ion and hydrochloric acid

Write down the chemical equations for the hydroxide ion (OH⁻) reacting with hydrochloric acid (HCl): OH⁻ (aq) + HCl (aq) → H₂O (l) + Cl⁻ (aq)

Step 4: Identify the ionic compound formed

In the reaction between the protonated 1,2-diaminoethane and hydrochloric acid, the following ionic compound is formed: H₂NCH₂CH₂NH₃⁺ (aq) + Cl⁻ (aq) → H₂NCH₂CH₂NH₃Cl (s) The ionic compound formed is H₂NCH₂CH₂NH₃Cl.

Key Concepts

1,2-Diaminoethane

1,2-Diaminoethane, also known by its IUPAC name 'ethane-1,2-diamine', is an organic compound with the molecular formula \( \mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2}\mathrm{NH}_{2} \). It is composed of an ethane backbone with two amino (\( -NH_{2} \) groups attached to each carbon atom. This structure allows 1,2-diaminoethane to act as a bidentate ligand in coordination chemistry, meaning it can form two bonds with a metal ion.

When dissolved in water, 1,2-diaminoethane can attract protons (\( H^+ \) ions) due to the electron pair on its nitrogen atoms, leading to the formation of a positively charged species. This process imparts basicity to the solution as hydroxide ions (\( OH^- \) are also produced. Essential to note is its versatile nature, allowing it to engage in reactions as a nucleophile because of its amine groups. Understanding the behavior of 1,2-diaminoethane in different environments is key to grasping its reactivity, especially in the context of acid-base chemistry.

Hydrochloric Acid Reaction

Hydrochloric acid (\( HCl \)) is a strong monoprotic acid, which means it has a single proton to donate. When it dissolves in water, it completely dissociates into hydrogen (\( H^+ \) ions, also known as protons) and chloride ions (\( Cl^- \)).

In an acid-base reaction involving hydrochloric acid, like the one with 1,2-diaminoethane, the hydrochloric acid acts as the acid (proton donor) while the other substance usually functions as a base (proton acceptor). In our case, 1,2-diaminoethane in its basic form accepts a proton from the hydrochloric acid, leading to the formation of its protonated species and chloride ions in solution. The chemical equation \( OH^- (aq) + HCl (aq) \rightarrow H_2O (l) + Cl^- (aq) \) illustrates this acid-base neutralization where a water molecule and a chloride ion are the products.

Ionic Compounds

Ionic compounds are formed from ions, which are atoms or molecules bearing a net electrical charge. They usually consist of positively charged ions called cations and negatively charged ions, anions, which are held together by the strong electrostatic forces known as ionic bonds.

In our exercise, the ionic compound is \( \mathrm{H}_{2}\mathrm{NCH}_{2}\mathrm{CH}_{2}\mathrm{NH}_{3}Cl \) which results from the reaction between protonated 1,2-diaminoethane and hydrochloric acid, yielding a cation (the protonated 1,2-diaminoethane \( [H_{2}NCH_{2}CH_{2}NH_{3}]^+ \) ) and an anion (chloride \( Cl^- \) from \( HCl \)). These ions are then attracted to each other due to opposite charges, forming an ionic solid. This particular compound highlights the interaction between a base, an acid, and their ability to generate an ionic substance as a result of their reaction.