Question

What are two kinds of molecules or ions that commonly function as weak bases?

Short answer

Two kinds of molecules or ions that commonly function as weak bases are Ammonia (NH3) and Amines, such as Methylamine (CH3NH2) and Ethylamine (C2H5NH2). Ammonia ionizes partially in water, forming ammonium ions (NH4+) and hydroxide ions (OH-), with a Kb value of approximately 1.8 × 10^-5. Amines, being organic compounds containing a nitrogen atom, also ionize partially in water, gaining a proton and forming their corresponding ammonium ions with the release of hydroxide ions (OH-).

Step-by-step solution

Understanding Weak Bases

A weak base is a chemical compound that does not completely ionize in water and only partially accepts protons (H+) from an acid in a chemical reaction. Weak bases have a higher pH value than strong bases. The extent to which they ionize in water depends on the equilibrium constant (Kb) for the base ionization reaction.

Identifying two common weak bases

We will provide two examples of molecules or ions that commonly function as weak bases: 1. Ammonia (NH3) 2. Amines (e.g., Methylamine (CH3NH2) and Ethylamine (C2H5NH2))

Discussing properties of Ammonia (NH3)

Ammonia (NH3) is a common weak base which exists as a colorless gas with a strong pungent odor. In its aqueous form, ammonia attracts a proton (H+) from water molecules to form ammonium ions (NH4+) and hydroxide ions (OH-). Its ionization in water can be represented by the following equation: \[NH3_{(aq)} + H2O_{(l)} \rightleftharpoons NH4^+_{(aq)} + OH^-_{(aq)}\] Ammonia has a Kb value of approximately 1.8 × 10^-5, meaning it only partially ionizes in water and does not accept protons as readily as a strong base.

Discussing properties of Amines

Amines are organic compounds containing a nitrogen atom bonded to hydrogen atoms, alkyl groups, or aryl groups. They can be classified as primary (RNH2), secondary (R2NH), or tertiary (R3N) amines. Two examples of amines that function as weak bases: 1. Methylamine (CH3NH2) - It has a Kb value of approximately 4.38 × 10^-4. 2. Ethylamine (C2H5NH2) - It has a Kb value of approximately 5.6 × 10^-4. When amines react with water, they gain a proton and form their corresponding ammonium ions with the release of hydroxide ions (OH-), increasing the pH of the solution. The ionization reaction for methylamine can be represented as following: \[CH3NH2_{(aq)} + H2O_{(l)} \rightleftharpoons CH3NH3^+_{(aq)} + OH^-_{(aq)}\]