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Chapter 16: Problem 88

Predict the stronger acid in each pair: (a) \(\mathrm{HCl}\) or HF; (b) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) or \(\mathrm{H}_{3} \mathrm{AsO}_{4} ;\) (c) \(\mathrm{HBrO}_{3}\) or \(\mathrm{HBrO}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) or \(\mathrm{HC}_{2} \mathrm{O}_{4} \overline{;} ;(\mathbf{e})\) benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\) or phenol \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}\right) .\)

Short Answer

Expert verified
The stronger acids among the given pairs are: (a) HCl (b) H₃AsO₄ (c) HBrO₃ (d) HC₂O₄⁻ (e) Benzoic acid (C₆H₅COOH)

Step by step solution

01

Evaluate Electronegativity Difference

In this case, it is helpful to compare the electronegativity difference between the central atoms, Cl and F. The general trend of the periodic table is that electronegativity increases as we move right across a period and decreases as we move down a group. Since chlorine is lower in the periodic table, it is less electronegative than fluorine.
02

Determine the Stronger Acid

Fluorine is more electronegative, so it holds the shared electrons more tightly. But this makes it less willing to give up a proton, and therefore, HF is a weaker acid than HCl. #b) H₃PO₄ vs H₃AsO₄#
03

Evaluate Atomic Size

Phosphorous and arsenic are in the same group but differ in the period they belong to. Since arsenic lies in a lower period, it is a larger atom compared to phosphorous.
04

Determine the Stronger Acid

A larger size atom stabilizes the negative charge on the conjugate base better. Therefore, H₃AsO₄ is a stronger acid than H₃PO₄. #c) HBrO₃ vs HBrO₂#
05

Evaluate the Number of Oxygen Atoms

Start by counting the number of oxygen atoms surrounding the central bromine atom. In HBrO₃, there are three oxygen atoms, whereas, in HBrO₂, there are only two oxygen atoms.
06

Determine the Stronger Acid

More oxygen atoms increase the electron-withdrawing nature of the molecule, which stabilizes the resulting negative charge on the conjugate base. Therefore, HBrO₃ is a stronger acid than HBrO₂. #d) H₂C₂O₄ vs HC₂O₄− #
07

Compare the number of acidic protons

H₂C₂O₄ has two acidic protons, whereas its counterpart HC₂O₄⁻ has only one acidic proton.
08

Determine the Stronger Acid

H₂C₂O₄ can donate two protons, and therefore its conjugate base has a higher charge (2-) compared to HC₂O₄⁻, which has one proton to donate and has a conjugate base with a charge of 1-. Due to the higher charge stabilization needed for the H₂C₂O₄ conjugate base, HC₂O₄⁻ is the stronger acid. #e) Benzoic acid (C₆H₅COOH) vs Phenol (C₆H₅OH)#
09

Examine the functional groups

Look at the functional groups of the two compounds. Benzoic acid has a carboxyl group (COOH), and phenol has a hydroxyl group (OH).
10

Evaluate resonance structures

For benzoic acid, the resulting negative charge from donating a proton is stabilized through resonance with the aromatic ring. In the case of phenol, the negative charge formed after donating a proton can also be stabilized through resonance, but to a lesser extent because the anion is less delocalized compared to benzoic acid.
11

Determine the Stronger Acid

Due to the higher stabilization of the negative charge through resonance in the carboxyl group, benzoic acid (C₆H₅COOH) is a stronger acid compared to phenol (C₆H₅OH).

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Most popular questions from this chapter

Determine the \(\mathrm{pH}\) of each of the following solutions \(\left(K_{a}\right.\) and \(K_{b}\) values are given in Appendix D): (a) \(0.095 \mathrm{M}\) hypochlorous acid, \((\mathbf{b}) 0.0085 \mathrm{M}\) hydrazine, (c) \(0.165 \mathrm{M}\) hydroxylamine.

Calculate \(\left[\mathrm{OH}^{-}\right]\) for each of the following solutions, and indicate whether the solution is acidic, basic, or neutral: (a) $\left[\mathrm{H}^{+}\right]=0.00010 \mathrm{M} ;(\mathbf{b})\left[\mathrm{H}^{+}\right]=7.3 \times 10^{-14} \mathrm{M} ;(\mathbf{c})\( a solution in which \)\left[\mathrm{OH}^{-}\right]$ is 100 times greater than \(\left[\mathrm{H}^{+}\right]\).

Based on their compositions and structures and on conjugate acid-base relationships, select the stronger base in each of the following pairs: (a) \(\mathrm{NO}_{3}^{-}\) or \(\mathrm{NO}_{2}^{-},\) (b) \(\mathrm{PO}_{4}^{3-}\) or \(\mathrm{AsO}_{4}^{3-}\), (c) \(\mathrm{HCO}_{3}^{-}\) or \(\mathrm{CO}_{3}^{2-}\).

At \(50^{\circ} \mathrm{C}\), the ion-product constant for $\mathrm{H}_{2} \mathrm{O}\( has the value \)K_{w}=5.48 \times 10^{-14} \cdot(\mathbf{a})$ What is the \(\mathrm{pH}\) of pure water at \(50^{\circ} \mathrm{C} ?\) (b) Based on the change in \(K_{w}\) with temperature, predict whether \(\Delta H\) is positive, negative, or zero for the autoionization reaction of water: $$ 2 \mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{OH}^{-}(a q) $$

Calculate the \(\mathrm{pH}\) of each of the following strong acid solutions: (a) \(8.3 \times 10^{-4} \mathrm{MHCl},(\mathbf{b}) 1.20 \mathrm{~g}\) of \(\mathrm{HNO}_{3}\) in \(500 \mathrm{~mL}\) of solution, $(\mathbf{c}) 2.0 \mathrm{~mL}\( of \)0.250 \mathrm{M} \mathrm{HClO}_{4}\( diluted to \)40.0 \mathrm{~mL}\(, (d) a solution formed by mixing \)25.0 \mathrm{~mL}\( of \)0.100 \mathrm{M} \mathrm{HBr}\( with \)25.0 \mathrm{~mL}\( of \)0.200 \mathrm{M} \mathrm{HCl}$.
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