Tag: chemistry

Questions Related to chemistry

How both the acids $\displaystyle HCl$ and $\displaystyle { HC } _{ 2 }{ H } _{ 3 }{ O } _{ 2 }$ are different?

chemistry chemical equilibrium and acids-bases dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. The first has less hydrogen in solution

  2. The second is highly ionized

  3. The second has more ionized hydrogen

  4. The first is highly ionized

Show answer
Correct Option: D
Explanation:

HCl undergoes complete ionization as it is a strong acid.
On the other hand, acetic acid  $HC _2H _3O _2$ is a weak acid and is ionized to a small extent.

What is the net effect of the common ion?

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. It reduces the solubility of the solute in the solution.

  2. It reduces the increases of the solute in the solution.

  3. It causes more product to be made.

  4. It causes more ions to form.

  5. There is no net effect overall.

Show answer
Correct Option: A
Explanation:

The net effect of the common ion is that it reduces the solubility of the solute in the solution.
The common ion effect is observed when the addition of an ion common to two solutes causes precipitation or reduces ionization.
Thus, if to a solution of weak electrolyte, a solution of strong electrolyte is added which furnishes an ion common to that furnished by the weak electrolyte, the ionization of the weak electrolyte is suppressed.
For example, ammonium hydroxide is a weak electrolyte and ionizes to a small extent to give ammonium ions and hydroxide ions.
$\displaystyle  NH _4OH \rightleftharpoons NH _4^+  +  OH^-$
A strong electrolyte NaOH is added which furnishes hydroxide ions that are common ions. This suppresses the equilibrium for the dissociation of ammonium hydroxide.
$\displaystyle  NaOH \rightarrow Na^+  + OH^-$

$Ca{SO} _{4}$ is somewhat soluble in water.
$I$. When ${H} _{2}{SO} _{4}$ is added to a solution of $Ca{SO} _{4}$, the solubility of the $Ca{SO} _{4}$ will be increased.
$II$. The addition of ${H} _{2}{SO} _{4}$ will lower the $pH$ of the solution.

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. Statement $I$ is true, Statement $II$ is true

  2. Statement $I$ is true, Statement $II$ is false

  3. Statement $I$ is false, Statement $II$ is true

  4. Statement $I$ is false, Statement $II$ is false

Show answer
Correct Option: C
Explanation:

When $H _2SO _4$ is added to a $CaSO _4$ solution, due to common ion effect, the solubility of $CaSO _4$ decreases. Further, as the acid concentration increases, the $pH$ of the solution lowers due to addition of $H _2SO _4$.

Hence, statement $I$ is false, statement $II$ is true.

What is the common ion effect?

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. When the addition of an ion common to two solutes causes precipitation or reduces ionization.

  2. When a molecule is added to a solution and causes precipitation or reduces ionization

  3. When the subtraction of an ion common to two solutes causes precipitation or reduces ionization.

  4. The effect of adding ions to a solution.

  5. When any ion is added to a solution and causes precipitation or reduces ionization.

Show answer
Correct Option: A
Explanation:

The common ion effect is observed when the addition of an ion common to two solutes causes precipitation or reduces ionization.
Thus, if to a solution of a weak electrolyte, a solution of strong electrolyte is added which furnishes an ion common to that furnished by the weak electrolyte, the ionization of the weak electrolyte is suppressed.

A monoprotic acid in $1.00M$ solution is $0.001$% ionised. The dissociation constant of acid is:

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. ${ \alpha }^{ 2 }C+\alpha K-K=0$

  2. ${ \alpha }^{ 2 }C-\alpha K-K=0$

  3. ${ \alpha }^{ 2 }C-\alpha K+K=0$

  4. ${ \alpha }^{ 2 }C+\alpha K+K=0$

Show answer
Correct Option: A
Explanation:

According to Ostwald's dilution law


$K=\cfrac { { \alpha  }^{ 2 }C }{ \left( 1-\alpha  \right)  } $

On solving, we get


$\alpha^2C+\alpha K-K=0$


Hence, the correct option is $\text{A}$

The ionisation constant of acetic acid is $1.8\times { 10 }^{ -5 }$.The concentration at which it will be dissociated to $2$% is:

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. $1M$

  2. $0.045M$

  3. $0.018M$

  4. $0.45M$

Show answer
Correct Option: B
Explanation:

When acetic acid is dissolved in water, it partially dissociates (2%).

Ionisation constant $ K _a=1.87\times 10^{-5}$
$K _a=\cfrac{C\alpha \times C\alpha}{C(1-\alpha)}$

We assume $\alpha\sim  0\Rightarrow 1-\alpha\sim 1$
$\Rightarrow 1.87\times 10^{-5}=\cfrac{C\alpha^2}{1}={C\times 0.02\times 0.02}$
$\Rightarrow C = \cfrac{1.87\times 10^{-5}}{0.02^2}$
$=0.0467M$
Correct answer is option-B.

Which pair will show common ion effect?

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. $Ba{ Cl } _{ 2 }+Ba{ \left( { NO } _{ 3 } \right) } _{ 2 }$

  2. $NaCl+HCl$

  3. ${ NH } _{ 4 }OH+{ NH } _{ 4 }Cl$

  4. $AgCN+KCN$

Show answer
Correct Option: C
Explanation:

Those ions will show common ion effect in which one or both them does not dissociate completely.


$NaCl$ and $HCl$ dissociate completely as one of them is acid and other is salt of strong acid and strong base.


$AgCN$ and $KCN$ dissociate completely as one of them is acid and other is salt of strong acid and strong base.

NH4OH is weak base to which NH4Cl is added which provides common $NH _4^{+}$ion dissociation of NH4OH is suppressed.

The dissociation constants of two acids $ H{ A } _{ 1 }$ and $H{ A } _{ 2 }$ are $3.0\times { 10 }^{ -4 }$ and $1.8\times { 10 }^{ -5 }$ respectively. The relative strengths of the acids will be:

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. $1:4$

  2. $4:1$

  3. $1:16$

  4. $16:1$

Show answer
Correct Option: B
Explanation:
The dissociation constants of $HA _1$ and $HA _2$ are $3\times10^{-4} $ and $1.8\times10^{-5}.$

The strength of an acid is directly proportional to square root of dissociation constants of acids. So relative strength of the given acids are:
$\dfrac { { (Acidic\ Strength }) _{ HA _1 } }{ { (Acidic\ Strength }) _{ HA _2} } =\dfrac { \sqrt { { (Dissociation\ Constant }) _{ HA _1} }  }{ \sqrt { { (Dissociation\ Constant }) _{ HA _2 } }  } $

 Relative Acidic Strength= $\dfrac { { (Acidic Strength }) _{ HA _1 } }{ { (Acidic Strength }) _{ HA _2 } } =\dfrac { \sqrt { 3.0\times { 10 }^{ -4 } }  }{ \sqrt { 1.8\times { 10 }^{ -5 } }  } =4.08=4(approx)$

relative strengths of acids will be $4:1.$

Which of the following pairs will show common ion effect?

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. Barium chloride + barium sulphate

  2. Silver cyanide + potassium nitrite

  3. Ammonium hydroxide + ammonium chloride

  4. Sodium chloride + hydrogen chloride

Show answer
Correct Option: C

When strong base $(NaOH)$ is added to the weak acid (acetic acid, ${ CH } _{ 3 }COOH$), then dissociation of acetic acid increases; this effect is known as:

chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

  1. Common ion effect

  2. Reverse ion effect

  3. Saltation effect

  4. Solubility effect

Show answer
Correct Option: B
Explanation:

$CH _3COOH\rightleftharpoons CH _3COO^{-}+H^+$
When $NaOH$ is added $H^+$ combines with $OH^{-}$ so concentration of $H^+$ decreases so equilibrium will shift towards right.
${ CH } _{ 3 }COOH+NaOH\longrightarrow { CH } _{ 3 }COONa+{ H } _{ 2 }O\quad $
Ionization of acetic acid will increase with the progress of its neutralization. This effect is called reverse ion effect.