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Chapter 15: Problem 145

True or false? If false, explain why each statement is wrong. (a) All Lewis acids are Brønsted acids. (b) The conjugate base of an acid always carries a negative charge. (c) The percent ionization of a base increases with its concentration in solution. (d) A solution of barium fluoride is acidic.

Short Answer

Expert verified
All statements are false. (a) Not all Lewis acids are Brønsted acids, they differ in their ability to donate protons or accept electron pairs. (b) The conjugate base of an acid doesn't always carry a negative charge, it depends on the specific acid. (c) The percent ionization of a base decreases with its concentration, not increases due to the common ion effect. (d) A solution of barium fluoride is basic, not acidic, as it increases the concentration of OH- ions in the water.

Step by step solution

01

Analysis and Answer for Statement (a)

Lewis acids and Brønsted acids fall under the broader category of acids but they are defined differently. A Brønsted acid is a substance that donates a proton (H+) in a reaction, whereas a Lewis acid is a substance that can accept an electron pair. Not all Lewis acids are capable of donating a proton, thus not all Lewis acids are Brønsted acids. Therefore, the statement is false.
02

Analysis and Answer for Statement (b)

The conjugate base of an acid is the species that remains after the acid has donated a proton. While it's commonly seen that conjugate bases carry a negative charge, this is not always the case. For example, the conjugate base of a neutral molecule like ammonia (NH3) is an anion (NH2-), but the conjugate base of an anion like the hydrogen sulfate ion (HSO4-) is a molecule (SO4^2-). Therefore, the statement is false.
03

Analysis and Answer for Statement (c)

The percent ionization (amount of base that is ionized in a solution) of a base is inversely proportional to its concentration. As concentration of the base in the solution increases, the percent ionization decreases due to the common ion effect. Therefore, the statement is false.
04

Analysis and Answer for Statement (d)

Regarding a solution of barium fluoride (BaF2), its nature, acid or base, depends on its ionization in water. Barium fluoride when dissolved in water creates barium ions (Ba2+) and fluoride ions (F2-). Now, the fluoride ions (F-) act as a base and tend to accept H+ ions from the water, forming HF and leaving OH- ions behind. This increases the concentration of hydroxide ions (OH-) in the water, thus making the solution basic, not acidic. Hence, the statement is false.

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Most popular questions from this chapter

Which of the following is the stronger acid: \(\mathrm{CH}_{2} \mathrm{ClCOOH}\) or \(\mathrm{CHCl}_{2} \mathrm{COOH}\) ? Explain your choice.

A solution contains a weak monoprotic acid HA and its sodium salt NaA both at \(0.1 M\) concentration. Show that \(\left[\mathrm{OH}^{-}\right]=K_{\mathrm{w}} / K_{\mathrm{a}}\).

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 \(K_{\mathrm{a}}\).)

Calculate the \(\mathrm{pH}\) of a \(0.24 \mathrm{M}\) solution of a weak base with a \(K_{b}\) of \(3.5 \times 10^{-6}\) .

Calcium hypochlorite \(\left[\mathrm{Ca}(\mathrm{OCl})_{2}\right]\) is used as a disinfectant for swimming pools. When dissolved in water it produces hypochlorous acid: $$ \begin{aligned} \mathrm{Ca}(\mathrm{OCl})_{2}(s)+2 \mathrm{H}_{2} \mathrm{O}(l) & \rightleftharpoons \\ & 2 \mathrm{HClO}(a q)+\mathrm{Ca}(\mathrm{OH})_{2}(s) \end{aligned} $$ which ionizes as follows: \(\mathrm{HClO}(a q) \rightleftharpoons \mathrm{H}^{+}(a q)+\mathrm{ClO}^{-}(a q)\) $$ K_{\mathrm{a}}=3.0 \times 10^{-8} $$ As strong oxidizing agents, both \(\mathrm{HClO}\) and \(\mathrm{ClO}^{-}\) can kill bacteria by destroying their cellular components. However, too high a HClO concentration is irritating to the eyes of swimmers and too high a concentration of \(\mathrm{ClO}^{-}\) will cause the ions to decompose in sunlight. The recommended pH for pool water is \(7.8 .\) Calculate the percent of these species present at this pH.
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