Board Paper of Class 12-Science 2015 Chemistry (SET 2) - Solutions

Name the reagents used in the following reactions:

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What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆_mixH for positive deviation?
Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult's law ? Give an example. VIEW SOLUTION

(a) Following reactions occur at cathode during the electrolysis of aqueous silver chloride solution :

$$\begin{gathered} {\mathrm{Ag}}^{+}\left(\mathrm{aq}\right) + {\mathrm{e}}^{-}\underset{ }{\to } \mathrm{Ag}\left(\mathrm{s}\right) \mathrm{E}° = +0.80 \mathrm{V} \\ {\mathrm{H}}^{+}\left(\mathrm{aq}\right) + {\mathrm{e}}^{-}\underset{ }{\to } \frac{1}{2}{\mathrm{H}}_2\left(\mathrm{g}\right) \mathrm{E}° = 0.00 \mathrm{V} \end{gathered}$$
On the basis of their standard reduction electrode potential (E°) values, which reaction is feasible at the cathode and why ?

(b) Define limiting molar conductivity. Why conductivity of an electrolyte solution decreases with the decrease in concentration ? VIEW SOLUTION

What are the transition elements? Write two characteristics of the transition elements. VIEW SOLUTION

(i) Write down the IUPAC name of the following complex:
[Cr(NH₃)₂Cl₂(en)]Cl (en = ethylenediamine)

(ii) Write the formula for the following complex:
Pentaamminenitrito-o-Cobalt (III). VIEW SOLUTION

(i) Draw the geometrical isomers of complex [Pt(NH₃)₂Cl₂].
(ii) On the basis of crystal field theory, write the electronic configuration for d⁴ ion if ∆₀ < P.
(iii) Write the hybridization and magnetic behaviour of the complex [Ni(CO)₄].
(At.no. of Ni = 28) VIEW SOLUTION

Calculate emf of the following cell at 25 °C :
$$\begin{gathered} \mathrm{Fe}\left|{\mathrm{Fe}}^{2+}\left(0.001 \mathrm{M}\right)\right| \left|{\mathrm{H}}^{+}\left(0.01 \mathrm{M}\right)\right| {\mathrm{H}}_2\left(\mathrm{g}\right) \left(1 \mathrm{bar}\right) \overline{)\mathrm{Pt} \left(\mathrm{s}\right)} \\ \mathrm{E}°\left({\mathrm{Fe}}^{2+} \overline{) \mathrm{Fe}}\right)=-0.44 \mathrm{V} \mathrm{E}°\left({\mathrm{H}}^{+} \overline{) {\mathrm{H}}_2}\right)=0.00 \mathrm{V} \end{gathered}$$ VIEW SOLUTION

Give reasons for the following observations :
(i) Leather gets hardened after tanning.
(ii) Lyophilic sol is more stable than lyophobic sol.
(iii) It is necessary to remove CO when ammonia is prepared by Haber's process. VIEW SOLUTION

Write the names and structures of the monomers of the following polymers

(i) Nylon-6, 6
(ii) PHBV
(iii) Neoprene VIEW SOLUTION

Predict the products of the following reactions :

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How do you convert the following :
(i) Phenol to anisole
(ii) Propan-2-ol to 2-methylpropan-2-ol
(iii) Aniline to phenol
(a) Write the mechanism of the following reaction :
$2{\mathrm{CH}}_3{\mathrm{CH}}_2\mathrm{OH}\stackrel{ {\mathrm{H}}^{+} }{\to }{\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_3$
(b) Write the equation involved in the acetylation of Salicylic acid. VIEW SOLUTION

(i) Which one of the following is a disaccharide : Starch, Maltose, Fructose, Glucose ?
(ii) What is the difference between fibrous protein and globular protein ?
(iii) Write the name of vitamin whose deficiency causes bone deformities in children. VIEW SOLUTION

Give reasons :
(a) n-Butyl bromide has higher boiling point than t-butyl bromide.
(b) Racemic mixture is optically inactive.
(c) The presence of nitro group (−NO₂) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions. VIEW SOLUTION

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated).

(Given : Molar mass of benzoic acid = 122 g mol⁻¹, K_f for benzene = 4.9 K kg mol⁻¹) VIEW SOLUTION

(i) Indicate the principle behind the method used for the refining of zinc.
(ii) What is the role of silica in the extraction of copper?
(iii) Which form of the iron is the purest form of commercial iron? VIEW SOLUTION

An element with molar mass 27 g mol⁻¹ forms a cubic unit cell with edge length 4.05 ✕ 10⁻⁸ cm. If its density is 2.7 g cm⁻³, what is the nature of the cubic unit cell? VIEW SOLUTION

(a) How would you account for the following :
(i) Actinoid contraction is greater than lanthanoid contraction.
(ii) Transition metals form coloured compounds

(b) Complete the following equation :
$2{\mathrm{MnO}}_4^{-}+6{\mathrm{H}}^{+}+5{\mathrm{NO}}_2^{-}\to$ VIEW SOLUTION

Mr. Roy, the principal 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 all resolved this issue by strictly banning the junk food in schools and to introduce healthy snacks and drinks like soup, lassi, milk etc. in school canteens. They also decided to make compulsory half an hour physical activities for the students in the morning assembly daily. After six months, Mr. Roy conducted the health survey in most of the schools and discovered a tremendous improvement in the health of students.

After reading the above passage, answer the following :
(i) What are the values (at least two) displayed by Mr. Roy ?
(ii) As a student, how can you spread awareness about this issue ?
(iii) What are tranquillizers ? Give an example.
(iv) Why is use of aspartame limited to cold foods and drinks ? VIEW SOLUTION

An aromatic compound 'A' of molecular formula C₇H₇ON undergoes a series of reactions as shown below. Write the structures of A, B, C, D and E in the following reactions :

                 

OR

(a) Write the structures of main products when aniline reacts with the following reagents :

(ii) HCl

(b) Arrange the following in the increasing order of their boiling point :

​(c) Give a simple chemical test to distinguish between the following pair of compounds :

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For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :

t/s	0	30	60
[CH3COOCH3] / mol L–1	0.60	0.30	0.15

(i) Show that it follows pseudo first order reaction, as the concentration of water remains constant.

(ii) Calculate the average rate of reaction between the time interval 30 to 60 seconds.

 (Given log 2 = 0.3010, log 4 = 0.6021)

Or

(a) For a reaction A + B → P, the rate is given by

Rate = k[A] [B]²

(i) How is the rate of reaction affected if the concentration of B is doubled ?

(ii) What is the overall order of reaction if A is present in large excess ?

(b) A first order  reaction takes 30 minutes for 50% completion. Calculate the time required for 90% completion of this reaction.

(log 2 = 0.3010)

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(a) Account for the following :

(ii) There is large difference between the melting and boiling points of oxygen and sulphur.

(b) Draw the structures of the following :

(ii) XeF4

OR

(i) Which allotrope of phosphorus is more reactive and why?

(ii) How the supersonic jet aeroplanes are responsible for the depletion of ozone layers?

(iii) F₂ has lower bond dissociation enthalpy than Cl₂. Why?

(iv) Which noble gas is used in filling balloons for meteorological observations?

(v) Complete the equation :​

${\mathrm{XeF}}_2+{\mathrm{PF}}_5\underset{}{\overset{ }{\to }}$​

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