Problem 14 - Chemistry The Science in Context

Question

Both KOH and \(\mathrm{Ba}(\mathrm{OH})_{2}\) are strong bases. Does this mean that solutions of the two compounds with the same molarity have the same ability to accept hydrogen ions? Why or why not?

Step-by-Step Solution

Answer

Answer: No, solutions of KOH and Ba(OH)2 with the same molarity do not have the same ability to accept hydrogen ions. This is because Ba(OH)2 produces twice the amount of hydroxide ions per mole compared to KOH, making it more effective in accepting hydrogen ions.

Step 1: Write the dissociation reactions of the strong bases

Write the chemical equations for the dissociation of KOH and Ba(OH)2 in water to form their respective ions. KOH(s) → K^+(aq) + OH^-(aq) Ba(OH)2(s) → Ba^2+(aq) + 2OH^-(aq)

Step 2: Calculate the moles of hydroxide ions produced

Determine the number of moles of hydroxide ions produced per mole of KOH and per mole of Ba(OH)2. For KOH: 1 mole of KOH produces 1 mole of OH^- For Ba(OH)2: 1 mole of Ba(OH)2 produces 2 moles of OH^-

Step 3: Compare the amount of hydroxide ions produced

Compare the number of hydroxide ions produced per mole of KOH and per mole of Ba(OH)2. For a solution with the same molarity, Ba(OH)2 will produce twice the amount of hydroxide ions compared to KOH.

Step 4: Conclusion

Based on the comparison of the amount of hydroxide ions produced per mole of the base, solutions of KOH and Ba(OH)2 with the same molarity will not have the same ability to accept hydrogen ions. This is because Ba(OH)2 produces more hydroxide ions (2 times as much) per mole compared to KOH, making it more effective in accepting hydrogen ions.

Key Concepts

Dissociation Reactions

When strong bases dissolve in water, they undergo a process called dissociation. This means that they break down into their individual ions. Both KOH (potassium hydroxide) and \(\text{Ba(OH)}_2\) (barium hydroxide) are strong bases. This means they dissociate completely in water.

Understanding dissociation is key to predicting how strong a base will conduct electricity or interact with acids. In the dissociation reactions:

• KOH separates into \(\text{K}^+\) ions and \(\text{OH}^-\) ions.
• \(\text{Ba(OH)}_2\) splits into \(\text{Ba}^{2+}\) ions and two \(\text{OH}^-\) ions.

Each dissociation reaction must be balanced to accurately express how many ions are produced. The thorough dissociation of a strong base in water is what gives it the ability to adjust the pH by accepting hydrogen ions (H⁺).

Hydroxide Ions

Hydroxide ions (OH⁻) are negatively charged ions that result from the dissociation of bases in water. They play a vital role in determining the basicity of a solution.

In any solution, the presence of hydroxide ions can neutralize hydrogen ions (H⁺), which are present in acidic solutions. The more OH⁻ ions there are, the more hydrogen ions they can react with, leading to a higher pH level in the solution.

In practice, a solution with a greater concentration of hydroxide ions is considered to be more basic or alkaline. Thus, comparing the production of hydroxide ions is essential in understanding the effectiveness of different bases, such as KOH and \(\text{Ba(OH)}_2\).

Molarity

Molarity is a concept that indicates the concentration of a solution. It is defined as moles of solute (substance dissolved) per liter of solution. In the context of bases like KOH and \(\text{Ba(OH)}_2\), molarity is crucial because it helps predict how many ions a solution will generate when dissolved.

If two solutions have the same molarity, they contain the same amount of solute per unit volume. However, because \(\text{Ba(OH)}_2\) produces more OH⁻ ions per mole than KOH, even at the same molarity, \(\text{Ba(OH)}_2\) will generate twice the number of hydroxide ions, impacting the solution's ability to accept hydrogen ions.

Calculating and comparing molarity helps in understanding the strength and efficacy of different chemical solutions.

KOH

Potassium hydroxide (KOH) is a strong base, meaning it completely dissociates in water to provide hydroxide ions. Each molecule of KOH dissolving in water produces one hydroxide ion (OH⁻).

Because it yields a single OH⁻ ion per formula unit, its effectiveness at increasing the base strength (or pH) of a solution is directly tied to its molarity.

Despite being strong, KOH is less effective per mole compared to bases that produce more hydroxide ions, such as \(\text{Ba(OH)}_2\). Yet, KOH's complete dissociation assures it is effective when used in situations requiring a strong base.

Ba(OH)2

Barium hydroxide, \(\text{Ba(OH)}_2\), is another strong base but differs from KOH by producing two hydroxide ions per molecule.

This makes \(\text{Ba(OH)}_2\) more efficient than KOH in terms of producing hydroxide ions, making it more effective at changing the hydrogen ion concentration of a solution. This characteristic makes \(\text{Ba(OH)}_2\) a particularly strong base when comparing solutions of the same molarity.

Understanding the additional hydroxide ions produced by \(\text{Ba(OH)}_2\) is key to recognizing its power in neutralizing acids in chemical reactions.