Sri Chaitanya Narayana IIT Academy Chemistry_Electrochemistry

Sri Chaitanya Narayana IIT AcademySri Sarvani Educational Society

COMMON CENTRAL OFFICE_MADHAPUR_HYDCHEMISTRY : ELECTROCHEMISTRY

Assignment-3Paragraph for Questions Nos. 1 to 3A hydrogen–oxygen fuel cell has a solid electrolyte, which is an ion exchange membrane. The membranes is impermeable to the reactant gases, but is permeable to hydrogen ions, which carry the current between the electrodes. To facilitate the operation of the cell at 40 to 60°C, the electrodes are covered with finely divided platinum that function as a catalyst. Water is drained out of the cell during operation. Fuel cells of this general type have been used successfully in the space program and are quite efficient. Their disadvantages for large–scale commercial application are that hydrogen presents storage problems, and platinum is an expensive catalyst. Cheaper catalysts have been found for higher temperature operation of hydrogen–oxygen fuel cells. Fuel cells that use hydrocarbons and air have been developed, but their power per unit weight is too low to make them practical in ordinary automobiles. Better catalysts are needed. A hydrogen–oxygen fuel cell may have an acidic or alkaline electrolyte. The half–cell reactions are

E° = 1.22 88 V

2H+ + E° = 0 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

E° = 1.2288V

or

E° = 0.4009 V

E° = – 0.8279 V ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

E° = 1.2288 V

To maximize the power per unit mass of an electrochemical cell, the electronic and electrolytic resistances of the cell must be minimized. Since fused salts have lower electrolytic resistances that aqueous solutions, high–temperature electrochemical cells are of special interest for practical applications. High temperature also allow the use of liquid metal electrode, which make possible higher current densities than solid electrodes.

1. If 560 mL of H2 gas at STP is fed into and is consumed by the fuel cell in 10 minutes, then what is the current output of the fuel cell? (A) 4A (B) 8A

(C) 16A (D) 12A

2. For a Hydrogen–Oxygen fuel cell if = – 285 kJ / mole, then what will be its thermodynamic efficiency under standard conditions(A) 0.91 (B) 0.41

(C) 0.63 (D) 0.83

3. Why are fuel cells not being used in daily life despite their very high efficiency (A) The fuels needed for their operation are rarely found in nature

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Sri Chaitanya Narayana IIT Academy Chemistry_Electrochemistry(B) Their operation always needs very high temperature (C) The catalyst used in fuel cells at normal temperature are very expensive (D)The design of fuel cells is so complicated that it is not feasible to construct these for daily life

applications. 4)

Equivalence conductance of saturated solution of BaSO4 is and specific

conductance is . Hence of is:A) B) C) D)

5) At the EMF of the cell Pb/PbCl2//AgCl/Ag is 0.5V and its temperature coefficient is

. If the heat of formation of is . The heat of formation of AgCl is,

A) B)

C) D)

6) In acidic medium, MnO2 is an oxidant as, . If the pH of the

solution is decreased by one unit, the electrode potential of the half cell Pt: will change byA) -0.118 V B) 0.118 V C) 0.236 V D) -0.236 V

7) Given,

The for the fuel cell reaction at 298K is,A) -474.8JK-1 B) -325.0JK-1 C) 474.8JK-1 D) 571.6JK-1

8) The heat of solution of anhydrous CuSO4 is and that of is . Calculate the heat of hydration of CuSO4.A) B) C) D)

9) Given the data at What is the value of log Ksp for AgI?A) B) C) D)

10) Calculate the equilibrium constant for the reaction, 2Fe3+ + 3I l 2Fe2+ + I3. The standard reduction

potentials in acidic conditions are 0.77 and 0.54 V respectively for Fe3+ / Fe2+ and I3 / I couples.

A) B) C) D)

11) A graph is plotted between Ecell and . The curve is linier with intercept on Ecell axis equals to

1.10V. Calculate Ecell for the cell

A) 1.23V B) 1.32V C) 1.07V D) 1.27V

12. concentra

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Sri Chaitanya Narayana IIT Academy Chemistry_ElectrochemistryAt what PH the above two half reactions will have same EMF values ? Assume the concentration of all the species to be unity. (assume 0.059=0.06)A) 1.2 B) 2.1 C) 1.5 D) 1.6

13. The standard potential of and electrodes are, respectively, 0.44 V and 0.40

V at 250 C; for the formation of and may be assumed to be independent of temperature. Calculate the temperature at which will begin to decompose in air (20% by volume of O2

A) B) C) D)

14. The EMF of the cell: is 0.45 V. 0.1 M KCl is 85% dissociated

and 0.1 M AgNO3 is 82% dissocated. Calculate the solubuluty product of at A) B) C) D)

15. Calculate the potential corresponding to the following cell given

;

A) – 0.42V B) 0.23v C) 0.32v D)-0.13v

16. At , after the addition of 110 mL of 0.1 N NaCl solution to 100 mL of 0.1 N Ag solution, the reduction potential of silver electrode placed in it is 0.36 V. Assuming activities to be identical with concentrations, calculate the solubility product of AgCl

A) B) C) D)

17. The standard potential of electrodes are respectively 0.344V and 0.40V

at ; for the formation of and may be assumed be independent of

temperature. Calculate the temperature at which will begin to decompose in air (20% by volume of

A) B) C) D)

18. A staurated calomel electrode is coupled through a salt bridge with a quinhydrone electrode dipping in 0.1M . The observed EMF at is 0.152V. Find the dissociation constant of . The oxidation potential of saturated calomel electrode = at .

A) B) C) D)

19. Calculate the EMF of the cell

A) B) C) D)

20. A cell initially contains and ions . calculate the change in cell potential after passage of 9.65A of current for 1 hr

A) decreases by 0.01V B) increases by 0.01V

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Sri Chaitanya Narayana IIT Academy Chemistry_Electrochemistry C) decreases by 0.05V D) increases by 0.05V

21. Match the following

List – I List – II A) Electrode reversible w.r.t cation p) B) Electrode reversible w.r.t anion q) C) Redox. Electrode r) D) Reference electrode s)

22. Calculate The minimum wt of NaOH required to be added in to consume all the present in R.H.S of cell of e.m.f of +0.701V at before its use.

A) B) C) D)

23. The equivalent condutance of monobasic acid at infinite dilution is . If the resistivity of

the solution containg 15g acid is 18.5 . what is the degree of disscussion of acid

A) B) C) D)

24. Calculate the for the reaction

;

A) B) C) D)

25. is Oxidised anodically. How much time is required to oxidise 26.08g of by a current of

0.5A A) B) C) D)

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Sri Chaitanya Narayana IIT Academy Chemistry_Electrochemistry

ELECTROCHEMISTRY – 3 KEY & HINTS

1.B 2.D 3.C 4. B 5.A 6.B 7.B

8.B 9.B 10. C 11.C 12.A 13.B 14.A

15.C 16.D 17.A 18.D 19. 20.B

21. 22. A 23.B 24.A 25.B

1. Cell reaction:

== 0 – (–0.44)= +0.44V

pH = pKa + 5.20 + log2 = 5.5, \ [H+] = 10–5.5M

n = 2

=

2. Moles of H2 =

\ Electric current = A.

3. DG° = – nFE° = – 2 × 96500 × 1.2288 Jmol–1 = – 237.160 kJ mol–1

Thermodynamic efficiency = 4) Conceptual

5)

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Sri Chaitanya Narayana IIT Academy Chemistry_Electrochemistry6)

7)

8)---------- (1)

------------(2)Subtracting (2) from (1)

\Heat of hydration of

9) Applying

10.

11.

12. Balance both the half vaction and apply nernst equation

in the urt equation

in the second equation

Then

13. Find using

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Sri Chaitanya Narayana IIT Academy Chemistry_ElectrochemistryThen

14.

15.

16.

17.

18. Conceptual

19.

20.

21. Conceptual

22. Find in R.H.Electrode using

23.

24.

25. .

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