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Chapter 18: Problem 6

Which of the following are Arrhenius bases? (a) \(\mathrm{H}_{3} \mathrm{~A} \mathrm{sO}_{4}\) (b) \(\mathrm{Ba}(\mathrm{OH})_{2}\) (c) \(\mathrm{HClO}\) (d) KOH

Short Answer

Expert verified
The Arrhenius bases are \(\mathrm{Ba}(\mathrm{OH})_{2}\) and KOH.

Step by step solution

01

Understanding Arrhenius Bases

Arrhenius bases are compounds that, when dissolved in water, increase the concentration of hydroxide ions (OH^-).
02

Analyze \(\mathrm{H}_{3} \mathrm{~A} \mathrm{sO}_{4}\)

This is arsenic acid, which is an acid, not a base as it donates protons (H+).
03

Analyze \(\mathrm{Ba}(\mathrm{OH})_{2}\)

Barium hydroxide is an Arrhenius base because it dissociates in water to produce barium ions (Ba^{2+}) and hydroxide ions (OH^-). \[\mathrm{Ba}(\mathrm{OH})_{2} \rightarrow \mathrm{Ba}^{2+} + 2\mathrm{OH}^{-}\]
04

Analyze \(\mathrm{HClO}\)

Hypochlorous acid (HClO) dissociates in water to form hydrogen ions (H+) and hypochlorite ions (ClO^-), indicating it is an acid.
05

Analyze KOH

Potassium hydroxide (KOH) is an Arrhenius base because it dissociates in water to produce potassium ions (K+) and hydroxide ions (OH^-). \[\mathrm{KOH} \rightarrow \mathrm{K}^{+} + \mathrm{OH}^{-}\]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Dissociation of Bases
When a base dissolves in water, it undergoes a process called dissociation. This means the base separates into its individual ions. For instance, when \(\text{KOH}\) (potassium hydroxide) dissolves, it splits into \(\text{K}^+\) (potassium ions) and \(\text{OH}^-\) (hydroxide ions). The same happens with \(\text{Ba(OH)}_2\) (barium hydroxide), which dissociates into \(\text{Ba}^{2+}\) (barium ions) and \(\text{OH}^-\) ions. A base must produce \(\text{OH}^-\) ions in water to be considered an Arrhenius base. Understanding dissociation is crucial because it reveals how substances behave in water- how they break apart and what ions they form.
Hydroxide Ion Concentration
In the context of Arrhenius bases, we focus on the concentration of hydroxide ions (\(\text{OH}^-\)) produced when the base dissolves in water. The more \(\text{OH}^-\) ions generated, the stronger the base. For example, \(\text{Ba(OH)}_2\) produces twice as many \(\text{OH}^-\) ions as potassium hydroxide (\(\text{KOH}\)). This is because each \(\text{Ba(OH)}_2\) molecule dissociates into two \(\text{OH}^-\) ions. This concept helps us compare the strength of different bases:
  • \(\text{KOH} \rightarrow \text{K}^+ + \text{OH}^-\)
  • \(\text{Ba(OH)}_2 \rightarrow \text{Ba}^{2+} + 2\text{OH}^-\)
Knowing this allows us to predict how a base will affect the pH of a solution.
Acid-Base Theory
Arrhenius bases form a part of the broader acid-base theory. According to Svante Arrhenius, an acid is a substance that increases the concentration of hydrogen ions (\(\text{H}^+\)) in water, while a base increases the concentration of hydroxide ions (\(\text{OH}^-\)). This definition helps us categorize substances based on their behavior in water. For example:
  • Arsenic acid (\(\text{H}_3\text{AsO}_4\)) increases \(\text{H}^+\) ions, so it's an acid.
  • Hypochlorous acid (\(\text{HClO}\)) increases \(\text{H}^+\) ions, so it's also an acid.
  • \(\text{KOH}\) and \(\text{Ba(OH)}_2\) increase \(\text{OH}^-\) ions, so they are bases.
This theory is fundamental for understanding chemical reactions and predicting the behavior of substances in different environments.

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Most popular questions from this chapter

Write balanced equations and \(K_{b}\) expressions for these Bronsted-Lowry bases in water: (a) Guanidine, \(\left(\mathrm{H}_{2} \mathrm{~N}\right)_{2} \mathrm{C}=\mathrm{NH}\) (the double-bonded \(\mathrm{N}\) is more basic) (b) Acetylide ion, \(\mathrm{HC} \equiv \mathrm{C}^{-}\)

A solution of propanoic acid \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\right),\) made by dissolving \(7.500 \mathrm{~g}\) in sufficient water to make \(100.0 \mathrm{~mL}\), has a freezing point of \(-1.890^{\circ} \mathrm{C}\). (a) Calculate the molarity of the solution. (b) Calculate the molarity of the propanoate ion. (Assume the molarity of the solution equals the molality.) (c) Calculate the percent dissociation of propanoic acid.

Liquid ammonia autoionizes like water: $$ 2 \mathrm{NH}_{3}(l) \longrightarrow \mathrm{NH}_{4}^{+}(a m)+\mathrm{NH}_{2}^{-}(a m) $$ where \((a m)\) represents solvation by \(\mathrm{NH}_{3}\). (a) Write the ion-product constant expression, \(K_{\text {am }}\) (b) What are the strongest acid and base that can exist in \(\mathrm{NH}_{3}(l) ?\) (c) \(\mathrm{HNO}_{3}\) and \(\mathrm{HCOOH}\) are leveled in \(\mathrm{NH}_{3}(l) .\) Explain with equations. (d) At the boiling point of ammonia \(\left(-33^{\circ} \mathrm{C}\right), K_{\text {unt }}=5.1 \times 10^{-27}\) Calculate \(\left[\mathrm{NH}_{4}^{+}\right]\) at this temperature. (c) Pure sulfuric acid also autoionizes. Write the ion-product constant expression, \(K_{\text {sulf }}\), and find the concentration of the conjugate base at \(20^{\circ} \mathrm{C}\left(K_{\mathrm{sulf}}=2.7 \times 10^{-4} \mathrm{at} 20^{\circ} \mathrm{C}\right)\)

The antimalarial properties of quinine \(\left(\mathrm{C}_{20} \mathrm{H}_{24} \mathrm{~N}_{2} \mathrm{O}_{2}\right)\) saved thousands of lives during the construction of the Panama Canal. This substance is a classic example of the medicinal wealth that tropical forests hold. Both \(\mathrm{N}\) atoms are basic, but the \(\mathrm{N}\) (colored) of the \(3^{\circ}\) amine group is far more basic \(\left(p K_{b}=5.1\right)\) than the \(N\) within the aromatic ring system \(\left(p K_{b}=9.7\right)\) (a) A saturated solution of quinine in water is only \(1.6 \times 10^{-3} M\). What is the pH of this solution? (b) Show that the aromatic N contributes negligibly to the pH of the solution. (c) Because of its low solubility, quinine is given as the salt quinine hydrochloride \(\left(\mathrm{C}_{20} \mathrm{H}_{24} \mathrm{~N}_{2} \mathrm{O}_{2} \cdot \mathrm{HCl}\right),\) which is 120 times more soluble than quinine. What is the pH of \(0.33 M\) quinine hydrochloride? (d) An antimalarial concentration in water is \(1.5 \%\) quinine hydrochloride by mass \((d=1.0 \mathrm{~g} / \mathrm{mL}) .\) What is the \(\mathrm{pH} ?\)

In each equation, label the acids, bases, and conjugate pairs: (a) \(\mathrm{NH}_{4}^{+}+\mathrm{CN}^{-} \rightleftharpoons \mathrm{NH}_{3}+\mathrm{HCN}\) (b) \(\mathrm{H}_{2} \mathrm{O}+\mathrm{HS}^{-} \rightleftharpoons \mathrm{OH}^{-}+\mathrm{H}_{2} \mathrm{~S}\) (c) \(\mathrm{HSO}_{3}^{-}+\mathrm{CH}_{3} \mathrm{NH}_{2} \rightleftharpoons \mathrm{SO}_{3}^{2-}+\mathrm{CH}_{3} \mathrm{NH}_{3}{ }^{+}\)
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