Question

What ions, atoms, or molecules are present after the following substances mix with water? For ionic compounds, you may want to refer to the solubility rules in Table 11.1. (a) \(\mathrm{HBr}\) (b) \(\mathrm{NH}_{4} \mathrm{Cl}\) (c) butanol, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\)

Short answer

After mixing with water, \(\mathrm{HBr}\) produces \(\mathrm{H^+}\) and \(\mathrm{Br^-}\), \(\mathrm{NH4Cl}\) produces \(\mathrm{NH4^+}\) and \(\mathrm{Cl^-}\), and butanol stays intact as \(\mathrm{CH3CH2CH2CH2OH}\).

Step-by-step solution

Analyzing Hydrobromic acid (HBr)

Hydrobromic acid (HBr) is a strong acid, meaning it completely ionizes in water. When it ionizes or dissociates in water, it forms hydronium ions \(H_3O^+\) and bromide ions \(Br^-\). So you can write this as follows: \[ \mathrm{HBr} \rightarrow \mathrm{H^+ + Br^-} \]

Analyzing Ammonium Chloride (NH4Cl)

Ammonium chloride (NH4Cl) is a soluble ionic compound. It will dissolve in water to form NH4+ and Cl- ions. You can write this as follows: \[ \mathrm{NH4Cl} \rightarrow \mathrm{NH4^{+} + Cl^{-}} \]

Analyzing Butanol (CH3CH2CH2CH2OH)

Butanol is an organic compound meaning it does not ionize or dissolve in water. This is because of its big hydrocarbon chain (CH3CH2CH2CH2) which is hydrophobic (water repelling). Therefore, no ions are produced when it mixes with water. This implies that the Butanol will stay as a separate layer on top of the water due to its less dense property. The separation can be written as follows: \[ \mathrm{CH3CH2CH2CH2OH} \rightarrow \mathrm{CH3CH2CH2CH2OH} + \mathrm{H2O} \]

Key concepts

Hydrobromic Acid

Hydrobromic acid, or HBr, is considered a strong acid, which has important implications on its behavior in aqueous solutions. A strong acid is characterized by its ability to completely ionize in water. This means that every molecule of HBr breaks apart to form ions when it comes into contact with water.

When HBr dissolves in water, it undergoes ionization to form two types of ions:

• Hydronium ions (\[\text{H}_3\text{O}^+\]
• Bromide ions (\[\text{Br}^-\]

Understanding this complete ionization is crucial because it implies that in a solution of HBr, you will only find these ions, without any remaining HBr molecules. The reaction is straightforward:\[\text{HBr} \rightarrow \text{H}^+ + \text{Br}^-\]

This complete dissociation means that HBr solutions are highly conductive due to the availability of free ions to carry electric current. This is a key property of strong acids like hydrobromic acid.

Ammonium Chloride

Ammonium chloride, known by its formula NH4Cl, behaves differently from strong acids like hydrobromic acid when it mixes with water. As a soluble ionic compound, ammonium chloride dissolves completely in water but its solubility leads to dissociation into ions rather than the complete ionization associated with strong acids.

When NH4Cl is added to water, it separates into two distinct ions:

• Ammonium ions (\[\text{NH}_4^+\]
• Chloride ions (\[\text{Cl}^-\]

The dissolution of NH4Cl can be written as:\[\text{NH}_4\text{Cl} \rightarrow \text{NH}_4^+ + \text{Cl}^-\]

This behavior is characteristic of many ionic compounds. They break apart into their component ions when dissolved, allowing the solution to conduct electricity. Ammonium chloride's solubility in water is a classic example of ionic compounds' tendency to dissociate into free ions, which contrasts with the behavior of covalently bonded organic molecules.

Butanol Chemistry

Butanol, with its chemical formula \(\text{C}_4\text{H}_9\text{OH}\), is an example of an organic compound that does not ionize in water. Unlike ionic or strong covalent compounds, organic compounds like butanol have large hydrocarbon chains that are hydrophobic, meaning they repel water.

When mixed with water, butanol does not break down into ions. Instead, it remains intact as a molecule, which is a typical behavior of many alcohols. This lack of ionization can be visualized as follows:\[\text{C}_4\text{H}_9\text{OH} \rightarrow \text{C}_4\text{H}_9\text{OH} + \text{H}_2\text{O}\]

The presence of the non-polar hydrocarbon chain is responsible for butanol’s limited interaction with water, causing it to not only avoid ionization but also form a separate layer above water when combined, due to its lower density. This hydrophobic interaction impacts butanol’s solubility and miscibility properties, making it an interesting study in chemistry due to its dual characteristics of alcohol functionality and hydrophobic hydrocarbon behavior.