Tag: electrochemistry

Questions Related to electrochemistry

What do you mean by equivalent Conductivity?

conductivity and its types electrochemistry

  1. It is defined as the conducting power of all the ions produced by dissolving one gram equivalent of an electrolyte in solution.

  2. It is defined as the conducting power of all the ions produced by dissolving ten gram equivalent of an electrolyte in solution.

  3. It is defined as the conducting power of all the ions produced by dissolving hundred gram equivalent of an electrolyte in solution.

  4. It is defined as the conducting power of all the ions produced by dissolving thousand gram equivalent of an electrolyte in solution.

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Correct Option: A
Explanation:

Equivalent Conductivity is defined as the conducting power of all the ions produced by dissolving one gram equivalent of an electrolyte in solution. It is expressed as and is related to specific conductance as. (M is Molarity of the solution)

The resistance of $1\ N$ solution of $CH _{3}COOH$ is $250\ ohm$ when measured in a cell of cell constant $1.15\ cm^{-1}$. The equivalent conductance will be:

conductivity and its types electrochemistry

  1. $4.6\ ohm^{-1} cm^{2} eq^{-1}$

  2. $9.2\ ohm^{-1} cm^{2} eq^{-1}$

  3. $18.4\ ohm^{-1} cm^{2} eq^{-1}$

  4. $0.023\ ohm^{-1} cm^{2} eq^{-1}$

Show answer
Correct Option: A
Explanation:

$K = C \times \dfrac {l}{A} = \dfrac {1}{250}\times 1.15 = 4.6\times 10^{-3}\ ohm^{-1} cm^{-1}$
$\wedge _{e} = K\times \dfrac {1000}{N} = 4.6\times 10^{-3} \times \dfrac {1000}{1} = 4.6\ ohm^{-1} cm^{2} eq^{-1}$.

The specific conductance of a $0.01\ M$ solution of $KCl$ is $0.0014\ ohm^{-1} cm^{-1}$ at $25^{\circ}C$. Its equivalent conductance is____________.

conductivity and its types electrochemistry

  1. $14$

  2. $140$

  3. $1.4$

  4. $0.14$

Show answer
Correct Option: B
Explanation:

$\kappa =0.0014\ S{ cm }^{ -1 }\ \Lambda _{ eq }=\cfrac { 1000\times \kappa  }{ C } \ C=0.01M\ { \Lambda  } _{ eq }=\cfrac{1000 \times 0.0014}{0.01}=140$

The resistance of a N/10 KCI solution is 245$\Omega $. Calculate the equivalent conductance of the solution if the electrodes in the cell are 4cm apart and each having an area of 7.0sq,cm.

conductivity and its types electrochemistry

  1. $23.32S{ cm }^{ 2 }{ eq }^{ -1 }$

  2. $23.23S{ cm }^{ 2 }{ eq }^{ -1 }$

  3. $2.332S{ cm }^{ 2 }{ eq }^{ -1 }$

  4. none of these

Show answer
Correct Option: A
Explanation:

Given resistance = 245$\Omega $

Formula for the specific conductance (K) = $ \dfrac{1}{R} $ $\times \dfrac{l}{a}$
= $ \dfrac{1}{245} $ $\times \dfrac{4}{7}$
 K = 2.33 $\times 10^-$$^3$ 
Formula for the euivalent conductance=  K $\times$ $\dfrac{1000}{C}$
= 2.33 $\times 10^-$$^3$ $\times 10000$
= 23.32S $cm^2$ eq $^-$$^1$

The equivalent conductance of a weak monobasic acid at infinite dilution is $100cm^3$ $eq^{-1}$ and that of its $0.01$M solution is $5cm^2$ $eq^{-1}$ at $25^o$C. The dissociation constant $K _a$ of the acid is:

conductivity and its types electrochemistry

  1. $2.5\times 10^{-4}$

  2. $5\times 10^{-4}$

  3. $1.25\times 10^{-5}$

  4. $2.5\times 10^{-5}$

Show answer
Correct Option: D
Explanation:

The degree of dissociation, $\alpha=\cfrac {\text{Equivalent conductance at given dilution}}{\text{Equivalent conductance at infinite dilution}}$

                                                   $=\cfrac {5cm^2eq^{-1}}{100cm^2eq^{-1}}=\cfrac {1}{20}$
For weak monobasic acid,
$K _a=\cfrac {C \alpha^2}{1-\alpha}$
       $=C\alpha^2(\because 1>> \alpha)$
       $=0.01\times \left(\cfrac {1}{20}\right)^2= 2.5 \times 10^{-5}$

Equivalent conductance and molar conductance of $Fe _2(SO _4) _3$ are related?

conductivity and its types electrochemistry

  1. $\bigwedge _e=\bigwedge _m$

  2. $\bigwedge _{eq} = \dfrac{\bigwedge _m}{3}$

  3. $\bigwedge _{eq} = 3 \bigwedge _m$

  4. $\bigwedge _{eq} = \dfrac{\bigwedge _m}{6}$

Show answer
Correct Option: D

Molar ionic conductance of ${Ca}^{+2}$ is $x$ $S{m}^{2}$ ${mole}^{-1}$. Equivalent conductance of calcium phosphate is ____ $S{m}^{2}g$ ${eq}^{-1}$

conductivity and its types electrochemistry

  1. $x+y$

  2. $(3x+2y)$

  3. $6(3x+2y)$

  4. $\cfrac{3x+2y}{6}$

Show answer
Correct Option: A
Explanation:

Calcium phosphate $\rightarrow { Ca } _{ 3 }{ \left( { PO } _{ 4 } \right)  } _{ 2 }$

ionic conductance of ${ Ca }^{ 2+ }=x$ ${ sm }^{ 2 }{ mol }^{ -1 }$
ionic conductance of ${ PO } _{ 4 }^{ 3- }=Y$ ${ sm }^{ 2 }{ mol }^{ - }$
${ Ca } _{ 3 }{ \left( { PO } _{ 4 } \right)  } _{ 2 }\rightarrow 3{ Ca }^{ 2+ }+2{ PO } _{ 4 }^{ 3- }$
$\therefore $  equivalent conductivity $=x+y$

Which of the following has least conductivity in aqueous solution?

conductivity and its types electrochemistry

  1. $CO(NH _3) _4Cl _3$

  2. $Co(NH _3) _3Cl _3$

  3. $Co(NH _3) _5Cl _3$

  4. $Co(NH _3) _6Cl _3$

Show answer
Correct Option: A
Explanation:

Conductivity $\alpha $ no. of ions dissociated in solution.

$Co{ \left( { NH } _{ 3 } \right)  } _{ 4 }{ Cl } _{ 3 }\rightarrow { \left[ Co{ \left( { NH } _{ 3 } \right)  } _{ 4 }{ Cl } _{ 2 } \right]  }^{ + }+{ Cl }^{ \left( - \right)  }$
                                                    2 ions
$Co{ \left( { NH } _{ 3 } \right)  }{ Cl } _{ 3 }\rightarrow \left[ Co\left( { NH } _{ 3 } \right) { \left( Cl \right)  } _{ 3 } \right] $
                                                          1 ion
$Co{ \left( { NH } _{ 3 } \right)  } _{ 5 }{ Cl } _{ 3 }\rightarrow { \left[ Co{ \left( { NH } _{ 3 } \right)  } _{ 5 }Cl \right]  }^{ 2+ }+2{ Cl }^{ \left( - \right)  }$
                                                          3 ions
$Co{ \left( { NH } _{ 3 } \right)  } _{ 6 }{ Cl } _{ 3 }\rightarrow { \left[ Co{ \left( { NH } _{ 3 } \right)  } _{ 6 } \right]  }^{ 3+ }+3{ Cl }^{ \left( - \right)  }$
                                                             4 ions
$\therefore  Co{ \left( { NH } _{ 3 } \right)  } _{ 6 }{ Cl } _{ 3 }$ has highest conductivity.

The equivalent conductance of $CH _3COONa, \ HCl$ and $NaCl$ at infinite dilution are $91, 426$ and $126 \ S \ cm^3 \ eq^{-1}$ respectively at $25^oC$. The equivalent conductance of $1 \ M \ CH _3COOH$ solution is $19.55 \ S \ cm^2 \ eq^{-1}$. The pH of the solution is:

conductivity and its types electrochemistry

  1. $5.3$

  2. $4.3$

  3. $2.3$

  4. $1.3$

Show answer
Correct Option: D
Explanation:

$\lambda^o _{CH _3COONa}= \lambda^o _{CH _3COO^-}+ \lambda^o _{Na}=91 \ Scm^2eq^{-1}$.....(i)

$\lambda^o _{HCl}= \lambda^o _{H}+ \lambda^o _{Cl^-}= 426 \ Scm^2eq^{-1}$.....(ii)

$\lambda^o _{NaCl}= \lambda^o _{Na}+ \lambda^o _{Cl^-}=126 \ Scm^2eq^{-1}$.....(iii)

$\lambda^o _{CH _3COOH}= \lambda^o _{CH _3COO^-}+ \lambda^o _{H^+}= (i) + (ii) – (iii) = 391 \ Scm^2eq^{-1}$

$ \lambda _{CH _3COOH}= 19.5 \ Scm^2eq^{-1}$ (given)

Degree of dissociation $= \cfrac {\lambda _m}{\lambda^o _m}= \cfrac {19.55}{391}=0.05$

$CH _3COOH \longrightarrow CH _3COO^- + H^+$

$1(1-0.05)$                $0.05$             $0.05$

$[H^+]=0.05 \ M$

$pH= -log [H^+]=1.3$

The electrolytic conductance is a direct measure of:

conductivity and its types electrochemistry

  1. resistance

  2. potential

  3. concentration

  4. dissociation

Show answer
Correct Option: A
Explanation:

By measuring conductance, we can measure resistance, by using formula.

$R=\cfrac{1}{C}$             C=conductance