Lewis, Brønsted-Lowry, and Arrhenius Definitions - College Chemistry

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Question

Identify the Bronsted-Lowry acid in the following equation:

$\text{H}_2\text{O}+\text{C}_3\text{H}_6\text{O}^-\rightarrow\text{OH}^-+\text{C}_3\text{H}_7\text{O}$

Answer

Recall that a Bronsted-Lowry acid donates a proton. From the equation, we can see that $\text{H}_2\text{O}$ becomes $\text{OH}^-$ , which it lost an $\text{H}^+$ , or a proton. Thus, water must be the Bronsted-Lowry acid.

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Question

Identify the Lewis Base in the following reaction:

$\text{CH}_3\text{CH}_2\text{CH}_2\text{SH}(aq)+\text{CH}_3\text{CH}_2\text{CH}_2\text{O}^-(aq)\rightleftharpoons \text{CH}_3\text{CH}_2\text{CH}_2\text{S}^-(aq)+\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}(aq)$

Answer

Recall that a Lewis base accepts a proton, while a Lewis acid donates a proton. Looking at the equation, we can see that $\text{CH}_3\text{CH}_2\text{CH}_2\text{O}^-$ becomes $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}$ . Since $\text{CH}_3\text{CH}_2\text{CH}_2\text{O}^-$ accepted a proton, it must be the Lewis base.

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Question

What is the pH of a solution?

Answer

PH is defined as $-log_{10}${H+}$ , where is hydronium concentration). In order to do this we simply take $-log_{10}${8M}$ :

$pH=-log_{10}${concentration of H+}$

= $pH=-log_{10}${8M}=.9$

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Question

Which type of acid is defined by its ability to produce hydrogen ions in aqueous solution?

Answer

There are three main definitions for acids and bases: the Lewis acids and bases, Bronsted-Lowry acids and bases, and Arrhenius acids and bases.

A Lewis acid is a species which can accept an electron pair from a donor. An example of a Lewis acid is $Fe^{2+}$ ; as a cation, it can accept an electron pair. A Lewis base is a species which can donate an electron pair. An example of a Lewis base is $OH^{-}$ ; as an anion, it can donate an electron pair.

A Bronsted-Lowry acid is a species which can donate a proton. An example of a Bronsted-Lowry acid is , which can donate its hydrogen ion. A Bronsted-Lowry base is a species which can accept a proton from a donor. An example of a Bronsted-Lowry base is $OH^{-}$ , which can accept a hydrogen ion in order to become water.

An Arrhenius acid is a species which releases hydrogen ions into solution. An example of an Arrhenius acid is $HNO_{3}$ . When this compound dissolves in aqueous solution, it produces $H^{+}$ and $NO_{3}^{-}$ . An Arrhenius base is a species which releases hydroxide ions into solution. An example of an Arrhenius base is . When this compound dissolves in aqueous solution, it produces $Li^{+}$ and $OH^{-}$ .

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Question

$\textrm{HClO}_{2}(aq)\textrm{ + H}_{2}\textrm{O}(l)\rightleftharpoons\textrm{ClO}_{2}\textrm{ }^{-}(aq)\textrm{ + H}_{3}\textrm{O}^{+}(aq)$

According to the Brønsted-Lowry definition of acids and bases, which species in the reaction are acids?

Answer

Remember a Brønsted-Lowry acid is defined as a proton donor.

In the forward reaction, $\textrm{HClO}_{2}$ is a proton donor. In the backward reaction, $\textup{H}_3\textup{O}^+$ is the proton donor.

The acids in this reaction are $\textrm{HClO}_{2}$ and $\textup{H}_3\textup{O}^+$ .

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