Q26 of 26 Page 1

Calculate emf and G for the following cell at 298 K

Mg (s)| Mg2+ (0.01M) || Ag+ (0.0001M) | Ag (s)


Given: E˚(Mg2+/Mg) = -2.37 V and E˚(Ag+/Ag) = +0.80 V


OR


(a) The conductivity of 0.001 mol/L solution of CH3COOH is 4.95 10-5 S/cm. Calculate it’s molar conductivity and degree of dissociation.


Given, (H+) = 349.6 S cm/mol


(CH3COO-) = 40.9 S cm/mol


(b) What is a fuel cell? Write its one advantage over the other ordinary cells.



We know that,

E˚cell = E˚C - E˚A


Ecell = 0.80 – (-2.37)


Ecell = 3.17 V


Anode reaction: Mg Mg2+ + 2e-


Cathode reaction: 2Ag+ + 2e- 2Ag (By multiplying by 2 to equate the number of electrons)


Cell reaction: Mg + 2Ag+ Mg2+ + 2Ag


According to Nernst Equation,


Ecell = E˚cell – log [Mg2+]/[Ag+]2


= 3.17 – log [0.1]/ [0.0001]2


= 3.17 – 0.0295 log [0.1]/ [1x 10-8]


= 3.17 – 0.0295[ log0.1 + log108]


= 3.17 – 0.0295[-1 + 8]


= 3.17 – 0.0295(7) = 3.17 – 0.2065


Ecell = 2.9635 V


G = -nfE˚cell


= -2 x 96500 x 3.17


G = -611.810 kJ/mol


OR


(a) We know that,


C = 0.001 mol/L and k = 4.95 x 10-5 S/cm


Molar conductivity =


= 4.95 10-5 x


= 49.5 S cm2/mol


CH3COOH = CH3COO- + H+


(CH3COOH)= (CH3COO-) + (H+)


= 40.9 + 349.6


= 390.5 S cm2/mol


Degree of dissociation = m / m


=


Degree of dissociation = 0.12


(b)


• A fuel cell is defined as a class of devices that converts chemical energy directly into electricity by chemical reactions.


• An example is a H2O2 fuel cell which was also used to produce energy during the Apollo Space Program.


• Fuel cells have higher efficiency than ordinary cells. They also do not produce a lot of pollution.


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22

A first order reaction takes 10 minutes for 25% decomposition. Calculate t1/2 for the reaction.

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Mr. Roy the principle of one reputed school organized a seminar in which he invited parents and principals to discuss the serious issue of diabetes and depression in students. They resolved this issue by strictly banning junk foods in schools and introducing healthy snacks and drinks like soup, lassi, milk etc. in the school canteens. They also made compulsory half an hour of daily physical activities for the students in the morning assembly. After six months, Mr. Roy conducted a health survey in most of the schools and discovered a tremendous improvement in the health of the students.

After reading the above passage, answer the following questions


(i) What are the values (at least 2) displayed by Mr. Roy?


(ii) As a student, how can you spread awareness about this issue?


(iii) What are tranquilizers? Give an example.


(iv) Why is the use of aspartame limited to cold foods and drinks?


 24

(a) Account for the following:

(i) Eu2+ is a strong reducing agent


(ii) Transition metals are coloured compounds


(iii) Zn has lowest enthalpy of atomization is the 3d series


(b) Complete the following equations:


(i) KMnO4


(ii) Cr2O72- + 14H+ + 6Fe2+


OR


(a) Account for the following


(i) Transition elements form interstitial compounds.


(ii) Mn3+ (3d4) is strongly oxidising whereas Cr2+ (3d4) is strongly reducing.


(iii) Transition metals have high melting point.


(b) What is ‘Misch metal’? Write one use.


 25

Write the structures of A, B, C and D in the following reactions:

(a)



(b) Distinguish between the following:


(i) CH3-CO-CH2CH3 and CH3-CH2-CH2-CHO


(ii) Ethanal and Ethanoic acid


(c) Write the structure of 4-Chloropentan-2-one


OR


(a) Write the structures of the main products when Propanal (CH3-CH2-CHO) reacts with the following reagents:


(i) Zn-Hg/ conc. HCl


(ii) H2N-OH/H+


(iii) HCN


(b) Arrange the following in decreasing order of their reactivity towards nucleophilic addition reaction


HCHO, CH3-CO-CH3, CH3-CHO


(c) Give the simplest chemical test to distinguish between the following pairs of compounds:


C6H5CHO and C6H5-CO-CH3