Chapter 17, Problem 64E

Classify each of the following statements as true or false:

a) All Brønsted-Lowry acids are Arrhenius acids.

b) All Arrhenius bases are Brønsted-Lowry bases, but not all Brønsted-Lowry bases are Arrhenius bases.

c) ${\text{HCO}}_{\text{3}}{}^{-}$ is capable of being amphoteric.

d) ${\text{HS}}^{-}$ is the conjugate base of ${\text{S}}^{2-}$.

e) If the species on the right side of an ionization equilibrium are present in greater abundance than those on the left, the equilibrium is favored in the forward direction.

f) ${\text{NH}}_{\text{4}}{}^{+}$ cannot act as a Lewis base.

g) Weak bases have a weak attraction for protons.

h) The stronger acid and the stronger base are always on the same side of a proton transfer reaction equation.

i) A proton transfer reaction is always favored in the direction that yields the stronger acid.

j) A solution with $\text{pH}=\text{9}$ is more acidic than one with $\text{pH}=4$.

k) A solution with $\text{pH}=3$ is twice as acidic as one with $\text{pH}=6$.

l) A pOH of $4.65$ expresses the hydroxide ion concentration of a solution in three significant figures.

Interpretation Introduction

(a)

Interpretation:

The statement that all Brønsted-Lowry acids are Arrhenius acids is to be classified as true or false.

Concept introduction:

According to Arrhenius theory, acids are the substances, which when added to water, release ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, release ${\text{OH}}^{-}$ ions. According to Brønsted-Lowry theory, acids are the substances, which when added to water, donate ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions.

Answer to Problem 64E

The statement that all Brønsted-Lowry acids are Arrhenius acids is true.

Explanation of Solution

According to Arrhenius theory, those substances, which when added to water, increase the ${\text{H}}^{\text{+}}$ ions in solution are known as acids. According to Brønsted-Lowry theory, the substances from which an ${\text{H}}^{\text{+}}$ ion, that is a proton, can be removed are known as acids. Therefore, all Brønsted-Lowry acids are Arrhenius acids.

Conclusion

The statement that all Brønsted-Lowry acids are Arrhenius acids is true.

Interpretation Introduction

(b)

Interpretation:

The statement that all Arrhenius bases are Brønsted-Lowry bases, but all Brønsted-Lowry bases are not Arrhenius bases is to be classified as true or false.

Concept introduction:

According to Arrhenius theory, acids are the substances, which when added to water, release ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, release ${\text{OH}}^{-}$ ions. According to Brønsted-Lowry theory, acids are the substances, which when added to water, donate ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions.

Answer to Problem 64E

The statement that all Arrhenius bases are Brønsted-Lowry bases, but all Brønsted-Lowry bases are not Arrhenius bases is true.

Explanation of Solution

According to Arrhenius theory, those substances, which when added to water, increase the ${\text{OH}}^{-}$ ions in solution are known as bases. According to Brønsted-Lowry theory, the substances that are capable of removing an ${\text{H}}^{\text{+}}$ ion from another compound are known as bases, that is, an ${\text{H}}^{\text{+}}$ ion is accepted by a Brønsted base. Due to the presence of ${\text{OH}}^{-}$ ions, all Arrhenius bases can accept an ${\text{H}}^{\text{+}}$ ion and behave as a Brønsted-Lowry base. Therefore, all Arrhenius bases are Brønsted-Lowry bases. There are some bases which are capable to accepting ${\text{H}}^{\text{+}}$ ion but they do not dissociate in water to give ${\text{OH}}^{-}$ ions. For example, ${\text{NH}}_{\text{3}}$. Therefore, all Brønsted-Lowry bases are not Arrhenius bases.

Conclusion

The statement that all Arrhenius bases are Brønsted-Lowry bases, but all Brønsted-Lowry bases are not Arrhenius bases is true.

Interpretation Introduction

(c)

Interpretation:

The statement that ${\text{HCO}}_{\text{3}}{}^{-}$ is capable of being amphoteric is to be classified as true or false.

Concept introduction:

A substance that has the capability of behaving as an acid as well as a base is known as an amphoteric substance. The substance behaves as an acid by releasing an ${\text{H}}^{+}$ ion and it behaves as a base by accepting an ${\text{H}}^{+}$ ion.

Answer to Problem 64E

The statement that ${\text{HCO}}_{\text{3}}{}^{-}$ is capable of being amphoteric is true.

Explanation of Solution

A substance is said to be amphoteric if it has the capability to behave as an acid and also as a base. The amphoteric substance acts as an acid by releasing an ${\text{H}}^{+}$ ion and it behaves as a base by accepting an ${\text{H}}^{+}$ ion.

The ${\text{HCO}}_{\text{3}}{}^{-}$ ion behaves as an acid by donating an ${\text{H}}^{+}$ ion to form ${\text{CO}}_{\text{3}}{}^{2-}$ ion as shown below.

${\text{HCO}}_{\text{3}}{}^{-}\to {\text{H}}^{+}+{\text{CO}}_{\text{3}}{}^{2-}$

The ${\text{HCO}}_{\text{3}}{}^{-}$ ion behaves as a base by accepting an ${\text{H}}^{+}$ ion to form ${\text{H}}_2{\text{CO}}_{\text{3}}$ ion as shown below.

${\text{HCO}}_{\text{3}}{}^{-}+{\text{H}}^{+}\to {\text{H}}_{\text{2}}{\text{CO}}_{\text{3}}$

Therefore, ${\text{HCO}}_{\text{3}}{}^{-}$ ion is capable of being amphoteric.

Conclusion

The statement that ${\text{HCO}}_{\text{3}}{}^{-}$ is capable of being amphoteric is true.

Interpretation Introduction

(d)

Interpretation:

The statement that ${\text{HS}}^{-}$ is the conjugate base of ${\text{S}}^{2-}$ is to be classified as true or false.

Concept introduction:

According to Brønsted-Lowry theory, acids are the substances, which when added to water, donate ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions.

Answer to Problem 64E

The statement that ${\text{HS}}^{-}$ is the conjugate base of ${\text{S}}^{2-}$ is false.

Explanation of Solution

A conjugate base is a species that is formed after donation of an ${\text{H}}^{\text{+}}$ ion by a Brønsted acid. The given species is ${\text{S}}^{2-}$. It does not possess an ${\text{H}}^{\text{+}}$ ion for donation and so, it cannot behave as a Brønsted acid. However, the species ${\text{S}}^{2-}$ can accept an ${\text{H}}^{\text{+}}$ ion to form ${\text{HS}}^{-}$ and therefore, ${\text{HS}}^{-}$ is the conjugate acid of ${\text{S}}^{2-}$. Therefore, ${\text{HS}}^{-}$ is not the conjugate base of ${\text{S}}^{2-}$.

Conclusion

The statement that ${\text{HS}}^{-}$ is the conjugate base of ${\text{S}}^{2-}$ is false.

Interpretation Introduction

(e)

Interpretation:

The statement that the equilibrium is favored in the forward direction if the species on the right side of an ionization equilibrium are present in greater abundance than those on the left, is to be classified as true or false.

Concept introduction:

A reaction is said to be in equilibrium if the rate at which the forward reaction takes place becomes equal to the rate at which the backward reaction takes place. If any of the factors that affect the equilibrium changes, then the reaction shifts in either forward or backward direction so that the equilibrium condition is reestablished.

Answer to Problem 64E

The statement that the equilibrium is favored in the forward direction if the species on the right side of an ionization equilibrium are present in greater abundance than those on the left, is true.

Explanation of Solution

Equilibrium always favors the formation of products, that is, the reaction will always proceed in the direction in which the products are in abundance. If the species on the right side of an ionization equilibrium are present in greater abundance than those on the left, it means that the products are more towards the right side. Therefore, in such cases, the equilibrium is favored in the forward direction.

Conclusion

The statement that the equilibrium is favored in the forward direction if the species on the right side of an ionization equilibrium are present in greater abundance than those on the left, is true.

Interpretation Introduction

(f)

Interpretation:

The statement that ${\text{NH}}_{\text{4}}{}^{+}$ cannot act as a Lewis base is to be classified as true or false.

Concept introduction:

According to Lewis theory, acids are the substances that accept a pair of electrons and bases are the substances that donate a pair of electrons.

Answer to Problem 64E

The statement that ${\text{NH}}_{\text{4}}{}^{+}$ cannot act as a Lewis base is true.

Explanation of Solution

According to Lewis theory, the species that can donate a pair of electrons can behave as Lewis bases. The species ${\text{NH}}_{\text{4}}{}^{+}$ does not possess an electron pair for donation. Therefore, ${\text{NH}}_{\text{4}}{}^{+}$ cannot act as a Lewis base.

Conclusion

The statement that ${\text{NH}}_{\text{4}}{}^{+}$ cannot act as a Lewis base is true.

Interpretation Introduction

(g)

Interpretation:

The statement that weak bases have a weak attraction for protons is to be classified as true or false.

Concept introduction:

Electrolytes are the substances that release ions when dissolved in water. The ease with which the dissociation of substances into ions takes place, determines the strength of that substance. According to Brønsted-Lowry theory, acids are the substances, which when added to water, donate ${\text{H}}^{\text{+}}$ ions and bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions.

Answer to Problem 64E

The statement that weak bases have a weak attraction for protons is true.

Explanation of Solution

According to Brønsted-Lowry theory, bases are substances, which when added to water, accept ${\text{H}}^{\text{+}}$ ions. A strong base is a substance that is capable of accepting ${\text{H}}^{\text{+}}$ ions easily, whereas, a weak base is unable to accept ${\text{H}}^{\text{+}}$ ions. So, a weak base does not attract protons easily. Therefore, weak bases have a weak attraction for protons.

Conclusion

The statement that weak bases have a weak attraction for protons is true.

Interpretation Introduction

(h)

Interpretation:

The statement that the stronger acid and the stronger base are always on the same side of a proton transfer reaction equation is to be classified as true or false.

Concept introduction:

Electrolytes are the substances that release ions when dissolved in water. The ease with which the dissociation of substances into ions takes place, determines the strength of that substance.

Answer to Problem 64E

The statement that the stronger acid and the stronger base are always on the same side of a proton transfer reaction equation is true.

Explanation of Solution

The substances that dissociate into positive and negative ions, when they are added to water, are known as electrolytes. If the substance undergoes complete dissociation into ions, then that substance is a strong electrolyte and if the substance is dissociated partially, then that substance is a weak electrolyte. A strong acid reacts with a strong base to form salt and water as the products. A strong acid always donates a proton to the strong base to form the products. Therefore, the stronger acid and the stronger base are always on the same side of a proton transfer reaction equation.

Conclusion

The statement that the stronger acid and the stronger base are always on the same side of a proton transfer reaction equation is true.

Interpretation Introduction

(i)

Interpretation:

The statement that a proton transfer reaction is always favored in the direction that yields the stronger acid is to be classified as true or false.

Concept introduction:

Electrolytes are the substances that release ions when dissolved in water. The ease with which the dissociation of substances into ions takes place, determines the strength of that substance.

Answer to Problem 64E

The statement that a proton transfer reaction is always favored in the direction that yields the stronger acid is false.

Explanation of Solution

The substances that dissociate into positive and negative ions, when they are added to water, are known as electrolytes. A strong acid reacts with a strong base to form salt and water as the products. A strong acid always donates a proton to the strong base to form the products. A strong acid forms a weak conjugate base after the donation of proton and a strong base forms a weak conjugate acid by accepting a proton. So, a strong acid reacts with a strong base to form a weak acid and a weak base. Therefore, a proton transfer reaction is not favored in the direction that yields the stronger acid.

Conclusion

The statement that a proton transfer reaction is always favored in the direction that yields the stronger acid is false.

Interpretation Introduction

(j)

Interpretation:

The statement that a solution with $\text{pH}=\text{9}$ is more acidic than the one with $\text{pH}=4$ is to be classified as true or false.

Concept introduction:

The pH of a solution can be determined by taking the negative logarithm of the concentration of hydrogen ions in a solution. The pOH of a solution can be determined by taking the negative logarithm of the concentration of ${\text{OH}}^{-}$ ions in a solution. The sum of pH and pOH is equal to $14$.

Answer to Problem 64E

The statement that a solution with $\text{pH}=\text{9}$ is more acidic than the one with $\text{pH}=4$ is false.

Explanation of Solution

The pH of a solution is the negative logarithm of the concentration of hydrogen ions in a solution. It determines the strength of acidic character of a compound. Acidic compounds have lower value of pH, that is, less than $7$, whereas basic compounds have higher value of pH, that is, more than $7$. Therefore, a solution with $\text{pH}=\text{9}$ is more basic than the one with $\text{pH}=4$.

Conclusion

The statement that a solution with $\text{pH}=\text{9}$ is more acidic than the one with $\text{pH}=4$ is false.

Interpretation Introduction

(k)

Interpretation:

The statement that a solution with $\text{pH}=3$ is twice as acidic as the one with $\text{pH}=6$ is to be classified as true or false.

Concept introduction:

The pH of a solution can be determined by taking the negative logarithm of the concentration of hydrogen ions in a solution. The pOH of a solution can be determined by taking the negative logarithm of the concentration of ${\text{OH}}^{-}$ ions in a solution. The sum of pH and pOH is equal to $14$.

Answer to Problem 64E

The statement that a solution with $\text{pH}=3$ is twice as acidic as the one with $\text{pH}=6$ is false.

Explanation of Solution

Consider the solution with $\text{pH}=3$.

The concentration of ${\text{H}}^{\text{+}}$ ions is calculated by the formula given below.

$\left[{\text{H}}^{\text{+}}\right]={\text{10}}^{-\text{pH}}$

Substitute the value of pH in the above expression.

$\begin{array}{rll}\left[{\text{H}}^{\text{+}}\right]& =& {\text{10}}^{-\text{pH}}\\ & =& {10}^{-3}\text{M}\end{array}$

Therefore, the concentration of ${\text{H}}^{\text{+}}$ ions in a solution having $\text{pH}=3$ is ${10}^{-3}\text{M}$.

Consider the solution with $\text{pH}=6$.

The concentration of ${\text{H}}^{\text{+}}$ ions is calculated by the formula given below.

$\left[{\text{H}}^{\text{+}}\right]={\text{10}}^{-\text{pH}}$

Substitute the value of pH in the above expression.

$\begin{array}{rll}\left[{\text{H}}^{\text{+}}\right]& =& {\text{10}}^{-\text{pH}}\\ & =& {10}^{-6}\text{M}\end{array}$

Therefore, the concentration of ${\text{H}}^{\text{+}}$ ions in a solution having $\text{pH}=6$ is ${10}^{-6}\text{M}$.

The twice of hydrogen ion concentration of ${10}^{-6}\text{M}$ is not equal to the hydrogen ion concentration of ${10}^{-3}\text{M}$. Therefore, solution with $\text{pH}=3$ is not twice as acidic as the one with $\text{pH}=6$.

Conclusion

The statement that a solution with $\text{pH}=3$ is twice as acidic as the one with $\text{pH}=6$ is false.

Interpretation Introduction

(l)

Interpretation:

The statement that a pOH of $4.65$ expresses the hydroxide ion concentration of a solution in three significant figures is to be classified as true or false.

Concept introduction:

The pH of a solution can be determined by taking the negative logarithm of the concentration of hydrogen ions in a solution. The pOH of a solution can be determined by taking the negative logarithm of the concentration of ${\text{OH}}^{-}$ ions in a solution. The sum of pH and pOH is equal to $14$.

Answer to Problem 64E

The statement that a pOH of $4.65$ expresses the hydroxide ion concentration of a solution in three significant figures is false.

Explanation of Solution

The value of pOH of $4.65$ possesses three significant figures. The pOH of a solution is the negative logarithm of the concentration of ${\text{OH}}^{-}$ ions in a solution. It does not express the hydroxide ion concentration of a solution. Therefore, a pOH of $4.65$ does not express the hydroxide ion concentration of a solution in three significant figures.

Conclusion

The statement that a pOH of $4.65$ expresses the hydroxide ion concentration of a solution in three significant figures is false.