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Chapter 15: Problem 113

Which of the following is a stronger base: \(\mathrm{NH}_{3}\) or \(\mathrm{PH}_{3} ?\) (Hint: The \(\mathrm{N}-\mathrm{H}\) bond is stronger than the \(\mathrm{P}-\mathrm{H}\) bond. \()\)

Short Answer

Expert verified
\(\mathrm{PH}_{3}\) (phosphine) is a stronger base than \(\mathrm{NH}_{3}\) (ammonia).

Step by step solution

01

Understand base properties

A base is a substance that can accept a proton (H+). The ability of a molecule to act as a base depends on its ability to donates its pair of non-bonding electrons (lone pair) to form a bond with a proton. The more readily it can donate this electron pair to form a bond with a proton (acid), the stronger the base it is considered to be.
02

Analyze bond strengths

From the hint, it is known that the strength of the \(\mathrm{N}-\mathrm{H}\) bond in ammonia is greater than the strength of the \(\mathrm{P}-\mathrm{H}\) bond in phosphine. This implies that it is harder to remove a hydrogen atom from ammonia than it is from phosphine.
03

Correlate bond strengths to base strength

Since a base donates its lone pair to form a bond with a proton, it means that the molecule from which it is harder to remove a hydrogen atom is less likely to donate its electron pair to a proton. Therefore, the molecule with the stronger bond (\(\mathrm{NH}_{3}\)) is a weaker base.
04

Choose the stronger base

Therefore, \(\mathrm{PH}_{3}\) (phosphine), which has the weaker \(\mathrm{P}-\mathrm{H}\) bond, is a stronger base. It more readily donates its lone pair to form a bond with a proton than does \(\mathrm{NH}_{3}\).

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Most popular questions from this chapter

What does the ionization constant tell us about the strength of an acid?

A \(0.400 M\) formic acid (HCOOH) solution freezes at \(-0.758^{\circ} \mathrm{C}\). Calculate the \(K_{\mathrm{a}}\) of the acid at that temperature. (Hint: Assume that molarity is equal to molality. Carry your calculations to three significant figures and round off to two for \(K_{\mathrm{a}}\).)

Write all the species (except water) that are present in a phosphoric acid solution. Indicate which species can act as a Brønsted acid, which as a Brønsted base, and which as both a Brønsted acid and a Brønsted base.

The \(\mathrm{pH}\) of a \(0.0642 \mathrm{M}\) solution of a monoprotic acid is \(3.86 .\) Is this a strong acid?

List four factors that affect the strength of an acid.
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