Tag: chemical changes

Quizzes (7) Questions (139)

Questions Related to chemical changes

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

An aqueous solution of volume 500 ml, when the reaction : $ 2Ag^+(aq) +Cu(s) \leftrightharpoons Cu^{2+}(aq) +2Ag(s) $ reached equilibrium, the concentration of $ Cu^{2+} $ ions was xM. to this solution, 500 ml of water is added.at new equilibrium , the concentration of $ Cu^{2+} $ ions would be 

  1. 2x M

  2. x M

  3. between x and 0.5 x M

  4. less than 0.5 x M
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Adding water increases the volume, which shifts the equilibrium. According to Le Chatelier's principle, the system will try to increase the number of ions. However, the dilution effect (concentration = moles/volume) dominates, leading to a decrease in concentration.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

When an electric current is passed through an aqueous solution of the following, the concentrations of cation as well as anion will not change for (assume constant volume of the electrolytic solution)

  1. $ C _{S} CI $
  2. $ KNO _{3}$
  3. $ AgNO _{3}$
  4. $ HCI$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

KNO3 is a strong electrolyte where both K+ and NO3- ions have high reduction/oxidation potentials compared to water. During electrolysis, water is preferentially electrolyzed, leaving the concentration of K+ and NO3- ions effectively unchanged.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

$NaCl$ is doped with $2\times { 10 }^{ -3 }$ mole % $Sr{Cl} _{2}$, the concentration of cation vacancies is

  1. $6.02\times { 10 }^{ 18 }{ mol }^{ -1 }$
  2. $1.204\times { 10 }^{ 19 }{ mol }^{ -1 }$
  3. $3.01\times { 10 }^{ 18 }{ mol }^{ -1 }$
  4. $1.204\times { 10 }^{ 21 }{ mol }^{ -1 }\quad $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Each Sr2+ ion replaces two Na+ ions in the lattice, creating one cation vacancy to maintain charge neutrality. 2 * 10^-3 mole % means 2 * 10^-5 moles of SrCl2 per mole of NaCl. This corresponds to 2 * 10^-5 * 6.022 * 10^23 vacancies per mole, which is 1.204 * 10^19.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Electrolysis of a solution of $ MnSO _{4}$ in aqueous sulphuric acid is a method for the preparation of $ MnO _{2}$ as per the reaction: $ Mn^{2+}(aq)+2H _{2}O\rightarrow MnO _{2}(s)+2H^{+}(aq)+H _{2}(g).$ Passing a current of 19.3 A for 2 h gives only 52.2 g of $MNO _{2}.$ The current efficiency is (Mn = 55)

  1. 8.33 %

  2. 83.33 %

  3. 41.67 %

  4. 100 %
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Calculate theoretical yield using Faraday's laws: Q = I * t = 19.3 * 7200 = 138960 C. Moles of electrons = Q / F = 138960 / 96500 = 1.44 mol. Reaction: Mn2+ + 2H2O -> MnO2 + 4H+ + 2e-. Moles of MnO2 = 1.44 / 2 = 0.72 mol. Mass = 0.72 * 87 = 62.64 g. Efficiency = (52.2 / 62.64) * 100 = 83.33%.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

A big irregular shaped vessel contained water, conductivity of which was $ 2.56 \times 10^{-3}\, S^{-1} \, m^{-1}.$ 585 g of NaCI was then added to the water and conductivity after the addition of Nacl, was found to be $ 3.06 \times 10^{-3}\,S^{-1}\, m^{-1}. $ The molar conductivity of Nacl at this concentration is $ 1.5 \times 10^{-2}\, S^{-1}\, mol^{-1}.$The capacity of vessel if it is fulfilled with water, is

  1. $ 3 \times 10^{4} 1$
  2. $ 30 \,1$
  3. $ 3 \times 10^{8} 1$
  4. $ 3 \times 10^{5} 1 $
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

The electrolysis of which electrolyte gives the same products in the fused state as well as in the aqueous solution state?

  1. NaCl

  2. KCl
  3. AuCl$ _{3}$
  4. BaCl$ _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

All have $Cl^-$ ions, $\therefore  Cl _2$, is released at anode
The element with reduction potential > red. potential of $H^+$ will give same results for aqueous and molter states.
From the given options only $SRP  of  Au^+  >  SRP  of  H^+$
Hence, for other salts in their aqueous solutions $H^+$  gets reduced

Hence, option C is correct.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

If mercury is used as cathode in the electrolysis of aqueous NaCl solution, the ions discharged at cathode are:

  1. H$^+$
  2. Na$^+$
  3. OH$^-$
  4. Cl$^-$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In presence of Hg electrode, sodium ions are discharged in the form of a mercury sodium amalgam and chloride ions are converted to chlorine. 
So, $Na^+$ ions discharged at cathode.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Electrolytic reduction of alumina to aluminium by Hall-Heroult process is carried out:

  1. in the presence of NaCl.

  2. in the presence of fluoride.

  3. in the presence of cryolite which forms a melt with lower melting temperature.

  4. in the presence of cryolite which forms a melt with higher melting temperature.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Pure alumina melts at about $ 2000^{0}C$ and is a bad conductor of electricity so fused cryolite and fluorspar is added to lower the melting point and the mixture melts at $ 900^0C$.