Chemistry

Electrochemistry and Solutions

205 Questions

Work through advanced chemistry questions focusing on electrochemistry and properties of solutions. Key themes include electrolytic conductivity, colloidal solutions, and solubility products. These concepts are frequently tested in JEE advanced, NEET, and university level chemistry competitive examinations.

Colloidal solutionsMolar conductivitySolubility productElectrolytic conductivityHydrolysis of saltsEquivalent conductivity

Electrochemistry and Solutions Questions

Multiple choice

Which of the following does not conduct electricity?

  1. Sugar solution

  2. Vinegar solution

  3. Lemon juice solution

  4. Caustic soda solution
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pure sugar (sucrose) is a covalent compound that does not dissociate into ions when dissolved in water. Since ions are required to carry an electric charge through a solution, sugar solution is a non-conductor.

Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

Solubility product of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ at ordinary temperature is $\displaystyle 1.96\times { 10 }^{ -11 }$. $\displaystyle pH$ of a saturated solution of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ will be

  1. 10.53

  2. 8.47

  3. 6.94

  4. 3.47
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\displaystyle { Mg\left( OH \right)  } _{ 2 }\rightleftharpoons M{ \underset { S }{ g }  }^{ 2+ }+2{ \underset { 2S }{ OH }  }^{ - }$
$\displaystyle { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=\left[ { Mg }^{ 2+ } \right] { \left[ { OH }^{ - } \right]  }^{ 2 }$
$\displaystyle \Rightarrow \quad { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=4{ S }^{ 3 }$
$\displaystyle 1.96\times { 10 }^{ -11 }=4{ S }^{ 3 }$
or $\displaystyle S={ \left[ \frac { 1.96\times { 10 }^{ -11 } }{ 4 }  \right]  }^{ 1/3 }$
or $\displaystyle S={ \left( 4.9\times { 10 }^{ -12 } \right)  }^{ 1/3 }$
$\displaystyle \therefore \quad S=1.69\times { 10 }^{ -4 }$
So, concentration of $\displaystyle \left[ { OH }^{ - } \right]=2S $
$\displaystyle \therefore \quad \left[ { OH }^{ - } \right] =3.38\times { 10 }^{ -4 }$
$\displaystyle \Rightarrow \quad pOH=-\log { \left[ { OH }^{ - } \right]  } $
$\displaystyle =-\log { \left[ 3.38\times { 10 }^{ -4 } \right]  } $
$\displaystyle \therefore \quad pOH=3.471$
$\displaystyle pH=14-pOH$
$\displaystyle =14-3.471$
$\displaystyle \therefore \quad pH=10.529$

Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

Although dissolution of $NH _{4}Cl$ in water is endothermic yet it dissolves because:

  1. $\Delta $ G is positive
  2. $\Delta $ H is positive
  3. $\Delta $ S is positive
  4. $\Delta $ A is positive
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Although the dissolution of ammonium chloride is endothermic (Delta H > 0), it dissolves spontaneously because the increase in entropy (Delta S > 0) is sufficiently large to make the overall Gibbs free energy change negative (Delta G = Delta H - T * Delta S < 0) at room temperature.

Multiple choice chemistry energetics and thermochemistry gibbs energy change and equilibrium gibbs free energy entropy and spontaneity

Concrete is produced from a mixture of cement, water and small stones. Small amount of gypsum, $CaSO _4\cdot 2H _2O$ is added in cement production to improve the subsequent hardening of concrete. 
The elevated temperature during the production of cement may lead to the formation of unwanted hemihydrate $CaSO _4\cdot \frac { 1 }{ 2 }H _2O$ according to reaction.

$CaSO _4\cdot 2H _2O(s)\rightarrow CaSO _4\cdot \frac { 1 }{ 2 }H _2O(s) + \frac { 3 }{ 2 }H _2O(g)$
The $\Delta _f H^{ \ominus }$ of $CaSO _4\cdot 2H _2O(s),\ CaSO _4\frac { 1 }{ 2 }H _2O(s),\ H _2O(g)$ are $-2021.0  kJ  mol^{ -1 }$, $-1575.0  kJ  mol^{ -1 }$ and $-241.8  kJ  mol^{ -1 }$ respectively. The respective values of their standard entropies are $194.0$, $130.0$ and $188.0  J  K^{ -1 }  mol^{ -1 }.$ 
$R = 8.314  J  K^{ -1 }  mol^{ -1 } = 0.0831  L  bar  mol^{ -1 }  K^{-1}$
Answer the follwoing questions on the basis of above information.
The value of equilibrium constant for reaction is:

  1. 0

  2. <1

  3. >1

  4. =1
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\Delta H^{ \ominus } = \Delta H^{ \ominus } _ { P } - \Delta H^{ \ominus } _{ R }; (for\quad 1\quad mol)$
$= \left[ -1575.0 kJ mol^{ -1 }-\frac { 3 }{ 2 } \times 241.8 \right] -\left[ -2021.0 kJ mol^{ -1 } \right] $
$= +83.3 kJ mol^{ -1 }$
For 1 Kg $CaSO _4\cdot 2H _2O$
Numebr of moles $=\frac { 1000}{ 172 }$
$= 5.81$
$\therefore$ Heat change for $5.81\quad mol\quad of\quad CaSO _4\cdot 2H _2O = 5.81\times 83.3 kJ mol^{ -1 }$
$=484 kJ mol^{ -1 }$
$\Delta G = \Delta H - T\Delta S$
$= 17.92 kJ$ ........ $(\Delta S = S _P - S _R)$
$\Delta G = -nRTln K$
$\therefore$ $K = e^{ -\Delta GlnRT } < 1$

Multiple choice chemistry coordination chemistry werner's theory werner's theory of coordination compounds coordination compounds

1 mole of co-ordinate compound $CoCl _3$ on reaction with excess AgNCl $143.5$gms of AgCl ppt . Then number of chloride ions satisfying both primary valency and secondary valency are?

  1. $2$
  2. $3$
  3. $1$
  4. $0$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Moles of $AgCl$ formed $=\cfrac{143.5}{143.5}=1$

$1$ mole of $CoCl _3$ gives $1$ mol of $AgCl$ ppt.
Secondary valence is the number of ions that are coordinated to metal ion. Here, $1Cl^-$ ion is not coordinated to the metal ion, due to which it gives $AgCl$ ppt. Hence, no. of chloride ions satisfying the given condition $=2.$

Multiple choice chemistry coordination chemistry werner's theory werner's theory of coordination compounds coordination compounds

The units of solubility product of silver chromate $(Ag 2CrO _4)$ will be _________.

  1. $mol^2L^{-2}$
  2. $mol^3L^{-3}$
  3. $mol L^{-1}$
  4. $mol L^{-2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
 Molar solubility is the number of moles of a substance (the solute) that can be dissolved per liter of solution before the solution becomes saturated. It can be calculated from a substance's solubility product constant (Ksp) and stoichiometry. The units are mol/L, sometimes written as M.

Multiple choice chemistry coordination chemistry werner's theory werner's theory of coordination compounds coordination compounds

which has the maximum conductivity in thier 0.1M solution?

  1. A) $\left[ Co{ (NH } _{ 3 }) _{ 3 }{ Cl } _{ 3 } \right] $
  2. B) $\left[ Co({ NH } _{ 3 }) _{ 4 }Cl \right] { Cl } _{ 2 }$
  3. C) $\left[ Co({ NH } _{ 3 }) _{ 5 }Cl \right] { Cl } _{ 2 }$
  4. D) $\left[ Co({ NH } _{ 3 }) _{ 6 } \right] { Cl } _{ 3 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The maximum conductivity is shown by that compound which have maximum ions on dissociation. Hence the compound $[Co(NH _3) _6]Cl _3$ have the maximum number of ions $[Co(NH _3) _6] + 3Cl^-$ = 4 ions and hence the correct answer is D.

Multiple choice

What is the overall reaction that takes place in a Zinc-Air battery during discharge?

  1. Zn + O2 → ZnO

  2. Zn + 2OH- → Zn(OH)2 + 2e-

  3. 2Zn + O2 → 2ZnO

  4. Zn + 2H2O → Zn(OH)2 + H2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The overall reaction in a Zinc-Air battery during discharge is the combination of zinc and oxygen to form zinc oxide.

Multiple choice

What is the mass of the products formed when 20 g of sodium (Na) reacts completely with 35.5 g of chlorine (Cl2)?

  1. 20 g

  2. 35.5 g

  3. 55.5 g

  4. 71 g
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to the law of conservation of mass, the total mass of the reactants (20 g Na + 35.5 g Cl2) is equal to the total mass of the products. Therefore, the mass of the products is 55.5 g.