Electrochemistry · Question 21

Consider the following half cell reaction Cr2O72-(aq) + 6e- + 14H+(aq) 2Cr3+(aq) + 7H2O( ) The reaction was conducted with the ratio of [ Cr3+]2[ Cr2O72-] = 10-6. The pH value at which the EMF of the half cell will become zero is . (nearest integer value) [Given: standard half cell reduction potential E Cr2O72-,H+/Cr3+ = 1.33 V, 2.303RTF = 0.059 V.]

Given below are two statements : In the light of the given statements, choose the correct answer from the options given below :

1. Both Statement I and Statement II are true
2. Statement I is true but Statement II is false
3. Both Statement I and Statement II are false
4. Statement I is false but Statement II is true

1 Faraday of electricity was passed through Cu2+(1.5 M, 1 L)/Cu and 0.1 Faraday was passed through Ag+(0.2 M, 1 L)/Ag electrolytic cells. After this the two cells were connected as shown below to make an electrochemical cell. The emf of the cell thus formed at 298 K is mV (nearest integer) [figure] Given : E Cu2+/Cu = 0.34 V E Ag+/Ag = 0.8 V 2.303RTF = 0.06 V

Given below are two statements : 1 M aqueous solutions of each of Cu(NO3)2, AgNO3, Hg2(NO3)2, Mg(NO3)2 are electrolysed using inert electrodes. Given: E0Ag+/Ag = 0.80 V, E0Hg22+/Hg = 0.79 V, E0Cu2+/Cu = 0.34 V and E0Mg2+/Mg = -2.37 V. In the light of the above statements, choose the most appropriate answer from the options given below :

1. Both Statement I and Statement II are incorrect
2. Statement I is incorrect but Statement II is correct
3. Statement I is correct but Statement II is incorrect
4. Both Statement I and Statement II are correct

On charging the lead storage battery, the oxidation state of lead changes from x1 to y1 at the anode and from x2 to y2 at the cathode. The values of x1, y1, x2, y2 are respectively :

1. 0, +2, +4, +2
2. +2, 0, 0, +4
3. +4, +2, 0, +2
4. +2, 0, +2, +4

The molar conductance of an infinitely dilute solution of ammonium chloride was found to be 185 S cm2 mol-1 and the ionic conductances of hydroxide and chloride ions are 170 and 70 S cm2 mol-1, respectively. If molar conductance of 0.02 M solution of ammonium hydroxide is 85.5 S cm2 mol-1, its degree of dissociation is given by x 10-1. The value of x is . (Nearest integer)

Correct order of limiting molar conductivity for cations in water at 298 K is :

1. H+ > Na+ > K+ > Ca2+ > Mg2+
2. H+ > Ca2+ > Mg2+ > K+ > Na+
3. Mg2+ > H+ > Ca2+ > K+ > Na+
4. H+ > Na+ > Ca2+ > Mg2+ > K+

The standard cell potential ( E cell ) of a fuel cell based on the oxidation of methanol in air that has been used to power television relay station is measured as 1.21 V. The standard half cell reduction potential for O2 ( E O2/H2O ) is 1.229 V. Choose the correct statement :

1. Reactants are fed at one go to each electrode.
2. Oxygen is formed at the anode.
3. The standard half cell reduction potential for the reduction of CO2 ( E CO2/CH3OH ) is 19 mV
4. Reduction of methanol takes place at the cathode.

40 mL of a mixture of CH3COOH and HCl (aqueous solution) is titrated against 0.1 M NaOH solution conductometrically. Which of the following statement is correct? [figure]

1. The concentration of CH3COOH in the original mixture is 0.005 M
2. The concentration of HCl in the original mixture is 0.005 M
3. CH3COOH is neutralised first followed by neutralisation of HCl
4. Point 'C' indicates the complete neutralisation of HCl

Consider the following electrochemical cell at standard condition. Au(s) | QH2, Q | NH4X(0.01 M) || Ag+(1 M) | Ag(s) Ecell = +0.4 V The couple QH2/Q represents quinhydrone electrode, the half cell reaction is given below: [figure] [Given : E0 Ag+/Ag = +0.8 V and 2.303RTF = 0.06 V] The pKb value of the ammonium halide salt (NH4X) used here is . (nearest integer)