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Chapter 16: Problem 49

Write the chemical equation for the base ionization of methylamine, \(\mathrm{CH}_{3} \mathrm{NH}_{2}\). Write the \(K_{b}\) expression for methylamine.

Short Answer

Expert verified
The ionization equation is \(\mathrm{CH}_3\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^{+} + \mathrm{OH}^-\) and \(K_b = \frac{[\mathrm{CH}_3\mathrm{NH}_3^+][\mathrm{OH}^-]}{[\mathrm{CH}_3\mathrm{NH}_2]}\).

Step by step solution

01

Identify the Reactants and Products

Methylamine (\(\mathrm{CH}_3\mathrm{NH}_2\)) is a weak base. When it ionizes in water, it accepts a proton from water, forming methylammonium ion (\(\mathrm{CH}_3\mathrm{NH}_3^{+}\)) and hydroxide ion (\(\mathrm{OH}^-\)). The chemical reaction is initialized as\(\text{Base} + \text{Water} \rightarrow \text{Conjugate Acid} + \text{Hydroxide Ion}\).
02

Write the Chemical Equation

Based on the reactants identified, write the chemical equation for the base ionization of methylamine:\[\mathrm{CH}_3\mathrm{NH}_2(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^{+}(aq) + \mathrm{OH}^-(aq)\].
03

Define the Equilibrium Expression for Base Ionization (\(K_b\))

For a base ionization, \(K_b\) describes the equilibrium constant relating to the concentration of products over reactants. The expression for methylamine is:\[K_b = \frac{[\mathrm{CH}_3\mathrm{NH}_3^+][\mathrm{OH}^-]}{[\mathrm{CH}_3\mathrm{NH}_2]}\].

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Key Concepts

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

Chemical Equation
A chemical equation represents a chemical reaction using symbols and formulas to illustrate the substances involved. In the scenario of base ionization, the equation shows how a weak base like methylamine reacts with water. Methylamine, denoted as \(\mathrm{CH}_3\mathrm{NH}_2\), interacts with water to form a methylammonium ion \(\mathrm{CH}_3\mathrm{NH}_3^+\) and a hydroxide ion \(\mathrm{OH}^-\). This interaction is depicted as:
  • \(\mathrm{CH}_3\mathrm{NH}_2(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^+(aq) + \mathrm{OH}^-(aq)\)
This equation indicates that methylamine accepts a proton from water. Furthermore, the double arrow \(\rightleftharpoons\) signifies an equilibrium where the reaction progresses in both forward and backward directions.
Equilibrium Constant
The equilibrium constant, in this case \(K_b\), quantifies the state of balance between reactants and products in a reversible reaction. It provides insight into the extent of ionization for weak bases like methylamine.
  • For the reaction \(\mathrm{CH}_3\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^+ + \mathrm{OH}^-\), the constant expression is \(K_b = \frac{[\mathrm{CH}_3\mathrm{NH}_3^+][\mathrm{OH}^-]}{[\mathrm{CH}_3\mathrm{NH}_2]}\)
This formula is derived from the concentration of each species at equilibrium, where brackets \([...]\) indicate molarity. A larger \(K_b\) value implies stronger base ionization, whereas a smaller value suggests weaker ionization. This concept helps predict how much of the base has converted into its ions in solution.
Weak Base
A weak base, such as methylamine, is a base that does not completely ionize in solution. Unlike strong bases, which dissociate entirely in water, weak bases do so only partially, leading to the presence of both non-ionized and ionized forms in equilibrium.
  • Methylamine's ionization is a reversible process, represented by the equation:\[\mathrm{CH}_3\mathrm{NH}_2 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^+ + \mathrm{OH}^-\]
This equilibrium reflects the weak ionizing nature of methylamine, where not all molecules convert to ions and a noticeable amount remains as molecules. Understanding the behavior and characteristics of weak bases helps in predicting and managing chemical reactions in solutions.
Methylamine
Methylamine, represented as \(\mathrm{CH}_3\mathrm{NH}_2\), is a simple aliphatic amine known for its characteristic fishy odor. As a weak base, it plays a significant role in organic and analytical chemistry.
  • When dissolved in water, methylamine accepts a proton from water to form the methylammonium ion \(\mathrm{CH}_3\mathrm{NH}_3^+\)
  • It also results in the production of hydroxide ions \(\mathrm{OH}^-\), contributing to the basicity of the solution
The reaction is an example of base ionization where equilibrium is involved, marked by:
  • \(\mathrm{CH}_3\mathrm{NH}_2(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{CH}_3\mathrm{NH}_3^+(aq) + \mathrm{OH}^-(aq)\)
Recognizing methylamine's properties and behavior aids in various chemical applications, from synthesizing pharmaceuticals to surface coating in industrial processes.

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Most popular questions from this chapter

\(K_{a}\) for formic acid is \(1.7 \times 10^{-4}\) at \(25^{\circ} \mathrm{C}\). A buffer is made by mixing \(529 \mathrm{~mL}\) of \(0.465 \mathrm{M}\) formic acid, \(\mathrm{HCHO}_{2}\), and \(494 \mathrm{~mL}\) of \(0.524 M\) sodium formate, \(\mathrm{NaCHO}_{2} .\) Calculate the \(\mathrm{pH}\) of this solution at \(25^{\circ} \mathrm{C}\) after \(110 . \mathrm{mL}\) of \(0.152 \mathrm{M}\) \(\mathrm{HCl}\) has been added to this buffer.

Phthalic acid, \(\mathrm{H}_{2} \mathrm{C}_{8} \mathrm{H}_{4} \mathrm{O}_{4},\) is a diprotic acid used in the synthesis of phenolphthalein indicator. \(K_{a 1}=1.2 \times\) \(10^{-3},\) and \(K_{a 2}=3.9 \times 10^{-6} .\) a Calculate the hydronium-ion concentration of a \(0.015 M\) solution. b What is the concentration of the \(\mathrm{C}_{8} \mathrm{H}_{4} \mathrm{O}_{4}{ }_{4}^{2-}\) ion in the solution?

Phosphorous acid, \(\mathrm{H}_{2} \mathrm{PHO}_{3},\) is a diprotic acid. Write equations for the acid ionizations. Write the expressions for \(K_{a 1}\) and \(K_{a 2}\)

a Draw a pH titration curve that represents the titration of \(50.0 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{NH}_{3}\) by the addition of \(0.10 M \mathrm{HCl}\) from a buret. Label the axes and put a scale on each axis. Show where the equivalence point and the buffer region are on the titration curve. You should do calculations for the \(0 \%, 30 \%, 50 \%,\) and \(100 \%\) titration points. b) Is the solution neutral, acidic, or basic at the equivalence point? Why?

Rantidine is a nitrogen base that is used to control stomach acidity by suppressing the stomach's production of hydrochloric acid. The compound is present in Zantac \(^{\mathbb{B}}\) as the chloride salt (rantidinium chloride; also called rantidine hydrochloride). Do you expect a solution of rantidine hydrochloride to be acidic, basic, or neutral? Explain by means of a general chemical equation.
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