Q29 of 53 Page 1

(a) Complete the following equations:

(i) Cr2O72- + 2OH- →


(ii) MnO4- + 4H+ +3e- →


(b) Account for the following:


(i) Zn is not considered as a transition element.


(ii) Transition metals form a large number of complexes.


(iii) The E0 value for the Mn3+/ Mn2+ couple is much more positive than that for the Cr3+/ Cr2+ couple.


Or


(i) With reference to structural variability and chemical reactivity, write the differences between lanthanoids and actinoids.


(ii) Name a member of the lanthanoid series which is well known to exhibit +4 oxidation state.


(iii) Complete the following equation:


MnO4- + 8H+ + 5e-→


(iv) Out of Mn3+ and Cr3+, which is more paramagnetic and why?


(Atomic no.: Mn= 25, Cr= 24)


(a) (i) Cr2O72-+ 2OH- → 2CrO42-+ H2O


(ii) MnO4- + 4H+ +3e-→ MnO2+ 2H2O


(b) (i) Zn is not considered a transition metal because it has fully filled d orbitals.


(ii) This is due to smaller ionic sizes / higher ionic charge and availability of d orbitals that transition metals form a large no. of complexes


(iii) The E0 value for the Mn3+/ Mn2+ couple is much more positive than that for the Cr3+/ Cr2+ couple because Mn2+ is more stable (3d5) than Mn3+(3d4). And Cr3+ is more stable due to t2g3/d3 configuration.


Or


(i)Lanthanoids Actinoids


Atomic/ionic radii does not show much variation / +3 is the most common oxidation state, in few cases +2 & +4. Atomic / ionic radii show much variation/Besides +3 oxidation state they exhibit +4,+5,+6,+7 also.


They are quite reactive. Highly reactive in finely divided state.


(ii) Cerium (Ce+4)


(iii) MnO4- + 8H+ + 5e-→ Mn2++4H2O


(iv) Mn3+ is more paramagnetic because Mn3+ has 4 unpaired electrons (3d4) therefore more paramagnetic whereas Cr3+ has 3 unpaired electrons (3d3)


More from this chapter

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27

On the occasion of World Health Day, Dr. Satpal organized a ‘health camp’ for the poor farmers living in a nearby village. After check-up, he was shocked to see that most of the farmers suffered from cancer due to regular exposure to pesticides and many were diabetic. They distributed free medicines to them. Dr. Satpal immediately reported the matter to the National Human Rights Commission (NHRC). On the suggestions of NHRC, the government decided to provide medical care, financial assistance, setting up of super-speciality hospitals for treatment and prevention of the deadly disease in the affected villages all over India.

(i) Write the values shown by
(a) Dr. Satpal
(b) NHRC.
(ii) What type of analgesics are chiefly used for the relief of pains of terminal cancer?
(iii) Give an example of artificial sweetener that could have been recommended to diabetic patients.


 28

(a) Define the following terms:
(i) Molarity
(ii) Molal elevation constant (Kb)

(b) A solution containing 15 g urea (molar mass = 60 g/mol) per litre of solution in water has the same osmotic pressure (isotonic) as a solution of glucose (molar mass = 180 g/mol) in water. Calculate the mass of glucose present in one litre of its solution.


OR


(a) What type of deviation is shown by a mixture of ethanol and acetone? Give reason.


(b) A solution of glucose (molar mass = 180 g/mol) in water is labelled as 10% (by mass). What would be the molality and molarity of the solution?


(Density of solution = 1.2 g/mL)


 30

(a) Write the products formed when CH3CHO reacts with the following reagents:

(i) HCN


(ii) H2N-OH


(iii) CH3CHOin the presence of dilute NaOH


(b) Give simple chemical tests to distinguish between the following pairs of compounds:


(i) Benzoic acid and Phenol


(ii) Propanal and Propanone


OR


(a) Account for the following:


(i) Cl-CH2COOH is stronger acid than CH3COOH


(ii) Carboxylic acids do not give reactions of carbonyl group.


(b) Write the chemical equations to illustrate the following name reactions:


(i) Rosenmund reduction


(ii) Cannizzaro’s reaction


(c) Out ofCH3CH2-CO-CH2CH3 and CH3CH2-CH2-CO-CH3, which gives iodoform test?


 1

Why is adsorption always exothermic ?