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Chapter 16: Problem 42

Determine whether each of the following is true or false: (a) All strong bases are salts of the hydroxide ion. (b) The addition of a strong base to water produces a solution of \(\mathrm{pH}>\)7.0 .(c) Because \(\mathrm{Mg}(\mathrm{OH})_{2}\) is not very soluble, it cannot be a strong base.

Short Answer

Expert verified
Based on the given step-by-step solution, the short answer is: (a) True - All strong bases are salts of the hydroxide ion, as they dissociate completely in water to form a high concentration of hydroxide ions (OH⁻). (b) True - The addition of a strong base to water produces a solution of pH > 7.0, as it increases the basicity of the solution. (c) False - Despite its low solubility, Mg(OH)₂ can still be considered a strong base due to its complete dissociation in water.

Step by step solution

01

Statement (a) - All strong bases are salts of the hydroxide ion.

A strong base is a substance that can dissociate completely in water to form a high concentration of hydroxide ions (OH⁻). Salts are ionic compounds that result from the neutralization reaction between an acid and a base. In this context, a salt of the hydroxide ion means it has a metal cation combined with a hydroxide anion (OH⁻). For example, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong bases and salts of the hydroxide ion. Thus, this statement is true.
02

Statement (b) - The addition of a strong base to water produces a solution of pH > 7.0.

The pH scale is used to determine the acidity or basicity of a solution. It ranges from 0 to 14, with 7 being neutral. A solution with a pH less than 7 is acidic, while a solution with a pH greater than 7 is basic. Since a strong base dissociates completely in water to produce a high concentration of hydroxide ions (OH⁻), it increases the basicity of the solution. This results in a pH value greater than 7. Therefore, this statement is true.
03

Statement (c) - Because Mg(OH)₂ is not very soluble, it cannot be a strong base.

Solubility refers to the ability of a substance to dissolve in a given solvent, such as water. In the case of Mg(OH)₂, it is considered a sparingly soluble substance, which means it does not dissolve well in water. However, the classification of a substance as a strong base or a weak base depends on the degree of dissociation of that substance in water. While Mg(OH)₂ is not very soluble, the small amount that does dissolve in water dissociates completely to form magnesium ions (Mg²⁺) and hydroxide ions (OH⁻). Therefore, Mg(OH)₂ can still be considered a strong base due to its complete dissociation in water, despite its low solubility. Thus, this statement is false.

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Most popular questions from this chapter

codeine \(\left(\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3}\right)\) is a weak organic base. \(\mathrm{A} 5.0 \times 10^{-3} \mathrm{M}\) solution of codeine has a pH of \(9.95 .\) Calculate the value of \(K_{b}\) for this substance. What is the \(\mathrm{pK}_{b}\) for this base?

Calculate the molar concentration of \(\mathrm{OH}^{-}\) in a 0.724 \(\mathrm{M}\) solution of hypobromite ion \(\left(\mathrm{BrO}^{-} ; K_{b}=4.0 \times 10^{-6}\right) .\) What is the pH of this solution?

Based on their compositions and structures and on conjugate acid-base relationships, select the stronger base in each of the following pairs: (a) \(\mathrm{BrO}^{-}\) or \(\mathrm{ClO}^{-},(\mathbf{b}) \mathrm{BrO}^{-}\) or \(\mathrm{BrO}_{2}^{-}\) (c) \(\mathrm{HPO}_{4}^{2-}\) or \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}.\)

The acid-dissociation constant for chlorous acid \(\left(\mathrm{HClO}_{2}\right)\) is \(1.1 \times 10^{-2} .\) Calculate the concentrations of \(\mathrm{H}_{3} \mathrm{O}^{+}, \mathrm{ClO}_{2}^{-}\) and \(\mathrm{HClO}_{2}\) at equilibrium if the initial concentration of \(\mathrm{HClO}_{2}\) is 0.0125 \(\mathrm{M} .\)

Identify the Lewis acid and Lewis base in each of the following reactions: (a) \(\mathrm{HNO}_{2}(a q)+\mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{NO}_{2}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l)\) (b) \(\mathrm{FeBr}_{3}(s)+\mathrm{Br}^{-}(a q) \rightleftharpoons \mathrm{FeBr}_{4}^{-}(a q)\) (c) \(\mathrm{Zn}^{2+}(a q)+4 \mathrm{NH}_{3}(a q) \rightleftharpoons \mathrm{Zn}\left(\mathrm{NH}_{3}\right)_{4}^{2+}(a q)\) (d) \(\mathrm{SO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{2} \mathrm{O}_{3}(a q)\)
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