Question

Which of the following solutions is the most basic? (a) \(0.6 \mathrm{M} \mathrm{NH}_{3}\), (b) \(0.150 \mathrm{M} \mathrm{KOH}\), (c) \(0.100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\).

Short answer

The most basic solution among the given options is (a) 0.6 M NH3, as it has the highest concentration of hydroxide ions (0.6 M).

Step-by-step solution

Identify the number of hydroxide ions each solute releases in the solution

Each solute in the given solutions releases a certain amount of hydroxide ions when dissolved in water. NH3, being a weak base, reacts with water to form NH4+ and OH- ions. KOH and Ba(OH)2 are strong bases and dissociate completely in the solution, forming their respective cations and OH- ions. (a) NH3 - releases 1 OH- ion (b) KOH - releases 1 OH- ion (c) Ba(OH)2 - releases 2 OH- ions

Calculate the concentration of hydroxide ions for each solution

Now that we know the number of hydroxide ions each solute releases, we can calculate the concentration of hydroxide ions in each solution by multiplying the given concentration of the solute with the number of hydroxide ions released. (a) [OH-] in NH3 solution = 0.6 M * 1 = 0.6 M (b) [OH-] in KOH solution = 0.150 M * 1 = 0.150 M (c) [OH-] in Ba(OH)2 solution = 0.100 M * 2 = 0.200 M

Compare the concentration of hydroxide ions in the solutions and determine which is the most basic

It's time to compare the calculated concentrations of hydroxide ions in the three solutions to find out which solution is the most basic. The higher the concentration of hydroxide ions, the more basic the solution. [OH-] in NH3 solution = 0.6 M [OH-] in KOH solution = 0.150 M [OH-] in Ba(OH)2 solution = 0.200 M Since the NH3 solution has the highest concentration of hydroxide ions (0.6 M), it is the most basic among the given solutions. Therefore, the answer is: (a) 0.6 M NH3

Key concepts

Basicity

Basicity refers to the ability of a substance to act as a base, which typically involves accepting protons or donating pairs of electrons. In aqueous solutions, a key indicator of basicity is the concentration of hydroxide ions (OH⁻) present. The more OH⁻ ions a substance can generate, the stronger its basicity. Basicity is also often associated with the pH scale, where basic solutions have a pH greater than 7. When comparing solutions, the one with the higher concentration of OH⁻ ions is deemed more basic. For example, in the given solutions, the ammonia (\( \text{NH}_3 \)) solution has a high basicity due to its relatively large amount of hydroxide ions compared to the others.

Concentration of Hydroxide Ions

The concentration of hydroxide ions in a solution determines its basicity. It directly relates to how many hydroxide ions (\( \text{OH}^- \)) are available per liter of solution. When a base dissolves in water, its dissociation determines how many hydroxide ions are released.

• Strong bases dissociate completely, releasing their maximum potential hydroxide ions.
• Weak bases only partially dissociate, producing fewer hydroxide ions.

In the exercise provided, the concentration of hydroxide ions was calculated by multiplying the molarity of the solution by the number of hydroxide ions each solute releases:

• For \( \text{NH}_3 \), which releases one OH⁻ ion: \[ \text{[OH}^-\text{] in } \text{NH}_3 = 0.6 \, \text{M} * 1 = 0.6 \, \text{M} \]
• For \( \text{KOH} \), which also releases one OH⁻ ion: \[ \text{[OH}^-\text{] in KOH} = 0.150 \, \text{M} * 1 = 0.150 \, \text{M} \]
• For \( \text{Ba(OH)}_2 \), releasing two OH⁻ ions: \[ \text{[OH}^-\text{] in } \text{Ba(OH)}_2 = 0.100 \, \text{M} * 2 = 0.200 \, \text{M} \]

This list shows how hydroxide ion concentration helps us determine that the \( \text{NH}_3 \) solution is the most basic due to its higher concentration of hydroxide ions.

Strong and Weak Bases

Bases are classified as either strong or weak based on their ability to dissociate in water and produce hydroxide ions. Strong Bases: These are characterized by their complete dissociation in water. They release all their potential hydroxide ions, making them highly basic. Examples include potassium hydroxide (\(\text{KOH}\)) and barium hydroxide (\(\text{Ba(OH)}_2\)). Because they dissociate fully, the concentration of OH⁻ equals their initial molarity (or is multiplied if more than one OH⁻ per molecule is released).Weak Bases: In contrast, weak bases do not fully dissociate in solution. They partially release hydroxide ions, which means their solutions usually have a lower hydroxide concentration compared to strong bases of similar molarity. An example is ammonia (\(\text{NH}_3\)), which partly converts to ammonium (\(\text{NH}_4^+\)) and hydroxide ions when dissolved.In practical terms, the more a base dissociates into hydroxide ions, the stronger it is considered to be, and this impacts our calculations of their respective hydroxide ion concentrations.