Q: The species: \$\displaystyle { H }_{ 2 }O,\;{ HCO }_{ 3 }^{ - },\;{ HSO }_{ 4 }^{ - }\$ and \${ NH }_{ 3 }\$ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

SpeciesConjugate acid Conjugate base \$\displaystyle H_2O\$\$\displaystyle H_3O^+\$ \$\displaystyle OH^-\$ \$\displaystyle HCO_3^-\$ \$\displaystyle H_2CO_3\$ \$\displaystyle CO_3^{2-}\$ \$\displaystyle HSO_4^-\$ \$\displaystyle H_2SO_4\$ \$\displaystyle SO_4^{2-}\$ \$\displaystyle NH_3\$ \$\displaystyle NH_4^+\$ \$\displaystyle NH_2^-\$

Q: Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) \$\displaystyle { OH }^{ - }\$ (b) \$\displaystyle { F }^{ - }\$ (c) \$\displaystyle { H }^{ + }\$ (d) \$\displaystyle { BCl }_{ 3 }\$.

(a) \$\displaystyle OH^- \$ ion can donate an electron pair. Hence, it acts as Lewis base.(b) \$\displaystyle F^- \$ ion can donate an electron pair. Hence, it acts as Lewis base.(c) \$\displaystyle H^+ \$ ion can accept an electron pair. Hence, it acts as Lewis acid.(d) \$\displaystyle BCl_3 \$ ion can accept an electron pair. Hence, it acts as Lewis acid.

Q: What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species.\$\displaystyle { HNO }_{ 2 },{ CN }^{ - },{ HClO }_{ 4 }{ F }^{ - },{ OH }^{ - },{ CO }_{ 3 }^{ 2- }\$ and \${ S }^{ 2- }\$

Conjugate acid base pairs differ by a proton.For example, \$\displaystyle HCl, Cl^- \$ represents conjugate acid base pair.The conjugate acid/base for the species \$\displaystyle { HNO }_{ 2 },\;{ CN }^{ - },\;{ HClO }_{ 4 }{ F }^{ - },\;{ OH }^{ - },\;{ CO }_{ 3 }^{ 2- }\$ and \$ { S }^{ 2- }\$are \$\displaystyle NO_2^-, \;HCN, \;ClO_4^-,\; HF,\; H_2O\$ (acid) or \$O^{2-}\$ (base), \$HCO_3^-\$ and\$ \;HS^- \$ respectively.

Q: A monoprotic acid in a \$0.1\$M solution ionises to \$0.001\%\$. Its ionization constant is:

Here the concentration \$C=0.1M\$ and \$\%\alpha=0.001\$Thus ionization constant \$K_a\$ of the acid can be given as,\$ \displaystyle K_a = C \alpha ^2 = 0.1 \times (\dfrac {0.001}{100})^2 = 1 \times 10^{-11}\$

Q: The ionization constant of acetic acid is \$\displaystyle 1.74\times { 10 }^{ -5 }\$. Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its \$\displaystyle pH\$.

The dissociation equilibrium is \$\displaystyle CH_3COOH \rightleftharpoons CH_3COO^- + H^+ \$.Let \$\displaystyle \alpha \$ be the degree of dissociation.The equilibrium concentrations of \$\displaystyle CH_3COOH, CH_3COO^-\$ and \$ H^+ \$ are \$\displaystyle c(1- \alpha), c(\alpha) \$ and \$c(\alpha) \$ respectively.The equilibrium constant expression is \$\displaystyle K_c = \frac {[CH_3COO^-][H^+]}{[CH_3COOH]} \$.\$\displaystyle K_c = \frac {(c\alpha)(c\alpha)}{c(1-\alpha)}\approx c\alpha ^2 \$\$\displaystyle \alpha = \sqrt {\frac {K_a}{c}} = \sqrt {\frac {1.74 \times 10^{-5}}{0.05}} = 1.865 \times 10^{-2} \$\$\displaystyle [CH_3CO^-] = [H^+] = c \alpha = 0.05 \times 1.865 \times 10^{-2} = 9.33 \times 10^{-4} M \$\$\displaystyle pH = -log [H^+] =-log (9.33 \times 10^{-4}) =3.03 \$The concentration of acetate ion and its pH are \$9.33 \times10 ^{-4}\$ and \$3.03\$ respectively.

Q: What will be the conjugate bases for the Bronsted acids \$\displaystyle HF,\;{ H }_{ 2 }{ SO }_{ 4 }\$ and \${ HCO }_{ 3 }^{ - }\$?

The conjugate bases for the Bronsted acids \$\displaystyle HF,{ H }_{ 2 }{ SO }_{ 4 }\$ and \$ { HCO }_{ 3 }^{ - }\$ are \$\displaystyle { F }^{ - },{ HSO }_{ 4 }^{ - } \$ and \${ CO }_{ 3 }^{ 2- }\$ respectively.

Question 1

Which one of the following is the strongest acid?

Accepted Answer

Strong acid means weak conjugate base.Strength of Conjugate base order:${ CCl }_{ 3 }CO{ O }^{ - }<{ CHCl }_{ 2 }CO{ O }^{ - }<CH_2ClCO{ O }^{ - }<{ CH }_{ 3 }CO{ O }^{ - }$So strongest acid is ${ CCl }_{ 3 }CO{ O }^{ - }$.

Question 2

The species: $\displaystyle { H }_{ 2 }O,\;{ HCO }_{ 3 }^{ - },\;{ HSO }_{ 4 }^{ - }$ and ${ NH }_{ 3 }$ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

Accepted Answer

SpeciesConjugate acid Conjugate base  $\displaystyle  H_2O$$\displaystyle  H_3O^+$ $\displaystyle  OH^-$  $\displaystyle  HCO_3^-$ $\displaystyle  H_2CO_3$ $\displaystyle  CO_3^{2-}$ $\displaystyle  HSO_4^-$ $\displaystyle  H_2SO_4$ $\displaystyle  SO_4^{2-}$ $\displaystyle  NH_3$ $\displaystyle  NH_4^+$ $\displaystyle  NH_2^-$

Question 3

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) $O H^{-}$ (b) $F^{-}$ (c) $H^{+}$ (d) $B C l_{3}$ .

Medium

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Accepted Answer

(a) $\displaystyle OH^- $ ion can donate an electron pair. Hence, it acts as Lewis base.(b) $\displaystyle F^- $ ion can donate an electron pair. Hence, it acts as Lewis base.(c) $\displaystyle H^+ $ ion can accept an electron pair. Hence, it acts as Lewis acid.(d) $\displaystyle BCl_3 $ ion can accept an electron pair. Hence, it acts as Lewis acid.

Question 4

Which of the following can act both as a Bronsted acid and a Bronsted base?

Accepted Answer

A Bronsted-Lowry acid is defined as substance that releases $H^+$ ions; a Bronsted-Lowry base is defined as substance that accepts $H^+$ ions. In the given option $O_2^+$ neither gives nor accepts $H^+$ ion. $HCl$ only gives $H^+$ thus is an acid. $Na_2CO_3$ can accept $H^+$ thus is a base. But $HSO_4^-$ can accept $H^+$ to form $H_2SO_4$ and can release one $H^+$ to form $SO_4^{2-}$, therefore it i=can act as both Bronsted acid and Bronsted base.

Question 5

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species.
$H N O_{2}, C N^{-}, H C l O_{4} F^{-}, O H^{-}, C O_{3}^{2 -}$ and $S^{2 -}$

Hard

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Accepted Answer

Conjugate acid base pairs differ by a proton.For example, $\displaystyle HCl, Cl^- $ represents conjugate acid base pair.The conjugate acid/base for the species $\displaystyle { HNO }_{ 2 },\;{ CN }^{ - },\;{ HClO }_{ 4 }{ F }^{ - },\;{ OH }^{ - },\;{ CO }_{ 3 }^{ 2- }$ and $ { S }^{ 2- }$are $\displaystyle NO_2^-, \;HCN, \;ClO_4^-,\; HF,\; H_2O$ (acid) or $O^{2-}$ (base), $HCO_3^-$ and$ \;HS^- $ respectively.

Question 6

The conjugate base of ${H}_{2}{PO}_{4}^{-}$ is:

Accepted Answer

The concept of conjugate Acid-Base pair was given by Lowry-Bronsted Theory.According to the theory:Acids are proton $(H^{+})$ donors.Bases are proton $(H^{+})$ acceptors.Hence, in order to get the conjugate base of a species, we should consider that substance as an acid and vice versa.For example, $H_{2}SO_{4} \rightarrow HSO_{4}^{-} + H^{+}$Therefore, conjugate base of $H_{2}SO_{4}$ is $HSO_{4}^{-}$.Using this logic, for the given example:$H_{2}PO_{4}^{-} \rightarrow HPO_{4}^{-2} + H^{+}$Hence, conjugate base of $H_{2}PO_{4}^{-}$ is $HPO_{4}^{-2}$.Option A is correct.

Question 7

A monoprotic acid in a $0.1$M solution ionises to $0.001\%$. Its ionization constant is:

Accepted Answer

Here the concentration $C=0.1M$ and $\%\alpha=0.001$Thus ionization constant $K_a$ of the acid can be given as,$ \displaystyle K_a = C \alpha ^2 = 0.1 \times (\dfrac {0.001}{100})^2 = 1 \times 10^{-11}$

Question 8

The ionization constant of acetic acid is $1.74 \times 10^{- 5}$ . Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its $p H$ .

Hard

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Accepted Answer

The dissociation equilibrium is $\displaystyle CH_3COOH \rightleftharpoons CH_3COO^- + H^+ $.Let $\displaystyle \alpha $ be the degree of dissociation.The equilibrium concentrations of $\displaystyle CH_3COOH, CH_3COO^-$ and $ H^+ $ are $\displaystyle c(1- \alpha), c(\alpha) $ and $c(\alpha) $ respectively.The equilibrium constant expression is $\displaystyle K_c = \frac {[CH_3COO^-][H^+]}{[CH_3COOH]} $.$\displaystyle K_c = \frac {(c\alpha)(c\alpha)}{c(1-\alpha)}\approx c\alpha ^2 $$\displaystyle \alpha = \sqrt {\frac {K_a}{c}} = \sqrt {\frac {1.74 \times 10^{-5}}{0.05}} = 1.865 \times 10^{-2} $$\displaystyle [CH_3CO^-] = [H^+] = c \alpha = 0.05 \times 1.865 \times 10^{-2} = 9.33 \times 10^{-4} M $$\displaystyle pH = -log [H^+] =-log (9.33 \times 10^{-4}) =3.03 $The concentration of acetate ion and its pH are $9.33 \times10 ^{-4}$ and $3.03$ respectively.

Question 9

What will be the conjugate bases for the Bronsted acids $\displaystyle HF,\;{ H }_{ 2 }{ SO }_{ 4 }$ and  ${ HCO }_{ 3 }^{ - }$?

Accepted Answer

The conjugate bases for the Bronsted acids $\displaystyle&#10; HF,{ H }_{ 2 }{ SO }_{ 4 }$ and $ { HCO }_{ 3 }^{ - }$ are &#10;$\displaystyle { F }^{ - },{ HSO }_{ 4 }^{ - } $ and ${ CO }_{ 3 }^{ 2- }$ respectively.

Question 10

Which of the following is a Lewis acid?

Accepted Answer

Lewis Acid is a species that accepts an electron pair (i.e., an electrophile) and will have vacant orbitals. In the given options $BF_3$ is a strong electrophile and has vacant orbital to accept electron lone pair. Thus it is a Lewis acid. Other three $H_2O, Cl^-$ and $NH_3$ have lone pair of electrons and act as lewis base.

Revise with Concepts

Arrhenius Theory of Acids and Bases

The Bronsted-Lowry Theory of Acids and Bases

Acids , Bases and Salts-Advanced

The Lewis Theory of Acids and Bases

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Arrhenius Theory

Lewis Acid and Bases

Which one of the following is the strongest acid?

The species: $H_{2} O, H C O_{3}^{-}, H S O_{4}^{-}$ and $N H_{3}$ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) $O H^{-}$ (b) $F^{-}$ (c) $H^{+}$ (d) $B C l_{3}$ .

Which of the following can act both as a Bronsted acid and a Bronsted base?

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species.
$H N O_{2}, C N^{-}, H C l O_{4} F^{-}, O H^{-}, C O_{3}^{2 -}$ and $S^{2 -}$

The conjugate base of $H_{2} P O_{4}^{-}$ is:

A monoprotic acid in a $0.1$ M solution ionises to $0.001 %$ . Its ionization constant is:

The ionization constant of acetic acid is $1.74 \times 10^{- 5}$ . Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its $p H$ .

What will be the conjugate bases for the Bronsted acids $H F, H_{2} S O_{4}$ and $H C O_{3}^{-}$ ?

Which of the following is a Lewis acid?

Revise with Concepts

Arrhenius Theory of Acids and Bases

The Bronsted-Lowry Theory of Acids and Bases

Acids , Bases and Salts-Advanced

The Lewis Theory of Acids and Bases

Quick Summary With Stories

Arrhenius Theory

Lewis Acid and Bases

Which one of the following is the strongest acid?

The species: H2​O,HCO3−​,HSO4−​ and NH3​ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) OH− (b) F− (c) H+ (d) BCl3​.

Which of the following can act both as a Bronsted acid and a Bronsted base?

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species. HNO2​,CN−,HClO4​F−,OH−,CO32−​ and S2−

The conjugate base of H2​PO4−​ is:

A monoprotic acid in a 0.1M solution ionises to 0.001%. Its ionization constant is:

The ionization constant of acetic acid is 1.74×10−5. Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its pH.

What will be the conjugate bases for the Bronsted acids HF,H2​SO4​ and HCO3−​?

Which of the following is a Lewis acid?

The species: $H_{2} O, H C O_{3}^{-}, H S O_{4}^{-}$ and $N H_{3}$ can act both as Bronsted acids and bases. For each case give the corresponding conjugate acid and base.

Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base: (a) $O H^{-}$ (b) $F^{-}$ (c) $H^{+}$ (d) $B C l_{3}$ .

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species.
$H N O_{2}, C N^{-}, H C l O_{4} F^{-}, O H^{-}, C O_{3}^{2 -}$ and $S^{2 -}$

The conjugate base of $H_{2} P O_{4}^{-}$ is:

A monoprotic acid in a $0.1$ M solution ionises to $0.001 %$ . Its ionization constant is:

The ionization constant of acetic acid is $1.74 \times 10^{- 5}$ . Calculate the degree of dissociation of acetic acid in its 0.05 M solution. Calculate the concentration of acetate ion in the solution and its $p H$ .

What will be the conjugate bases for the Bronsted acids $H F, H_{2} S O_{4}$ and $H C O_{3}^{-}$ ?