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RBSE 12th Chemistry Model Paper Set 8 with Answers in English

April 11, 2022 by Fazal Leave a Comment

Students must start practicing the questions from RBSE 12th Chemistry Model Papers Model Paper Set 8 with Answers in English Medium provided here.

RBSE Class 12 Chemistry Model Paper Set 8 with Answers in English

Time: 2 Hours 45 Min
Maximum Marks: 56

General Instruction to the Examinees :

  • Candidate must write first his/her roll No. on the question paper compulsory.
  • All the questions are compulsory.
  • Write the answer to each question in the given answer book only.
  • For questions having more than one part the answers to those parts are to be written together in continuity.

Section-A
Multiple Choice Questions (MCQs)

Question 1.
Choose the correct option:
(i) Amongst the following ion which one has the highest paramagnetism? (1)
(a) [Cr(H2O)6]3+
(b) [Fe(H2O)6]2+
(c) [CU(H2O)6]3+
(d) [Zn(H2O)6]2+
Answer:
(b) [Fe(H2O)6]2+

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

(ii) Which forms interstitial compounds? (1)
(a) Fe
(b) Co
(c) Ni
(d) All of these
Answer:
(d) All of these

(iii) Which of the following has highest molar conductivity? (1)
(a) Diamminedichloro platinum (II)
(b) Tetraamminedichlorocobalt (IV) chloride
(c) Potassium hexacyanoferrate (II)
(d) Hexaaquochromiuih (III) chloride
Answer:
(b) Tetraamminedichlorocobalt (IV) chloride

(iv) On treatment with methyl alcohol glucose gives: (1)
(a) α-methylglucoside
(b) β-methyl glucoside
(c) Bothe (a) and (b)
(d) None of these
Answer:
(c) Bothe (a) and (b)

(v) Which compound is obtained during the complete hydrolysis of cellulose? (1)
(a) D-glucose
(b) L-glucose
(c) D-fructose
(d) D-ribose
Answer:
(a) D-glucose

(vi) Which of the following is gem-di halide. (1)
(a) CH3CHBr2
(b) BrCH2CH2Br
(c) CH3CHBrCH2Br
(d) CH3CHBrCH2CH2Br
Answer:
(a) CH3CHBr2

(vii) Formaldehyde on reacting with ammonia gives: (1)
(a) Paraformaldehyde
(b) Urotropin
(c) Formose
(d) Bakelite
Answer:
(b) Urotropin

(viii) Formaldehyde on heating with KOH gives: (1)
(a) Acetylene
(b) Methane
(c) Methanol
(d) Ethyl formate
Answer:
(c) Methanol

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

(ix) In Hinesberg’s test, the product of which amine does not dissolve in NaOH? (1)
(a) CH3CH2NH2
(b) (CH3)2CHNH2
(c) CH3NHCH3
(d) CH3N(CH3)2
Answer:
(c) CH3NHCH3

Question 2.
Fill in the Blanks:
(i) Packing efficiency, of ccp is _____________ . (1)
Answer:
74%

(ii) [Pt(NH3)Cl2] complex is known as _____________ (1)
Answer:
platin

(iii) _____________ compounds are used as refrigrents. (1)
Answer:
freons

(iv) Vitamin C is a _____________ soluble vitamin. (1)
Answer:
water

Question 3.
Very Short Answer Type Questions:
(i) Name the chief ores of aluminium and zinc. (1)
Answer:
Chief ore of aluminium is bauxite (AlOx (OH)3 – 2x) where, 0 < x < 1 and of zinc is zinc blende or sphalerite (Zns).

(ii) Write the IUPAC name of Ph-CH=CH-CHO.
Answer:
IUPAC name: 3-phenylprop-2-enal.

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

(iii) Silver atom has completely filled d-orbitals (4d10) in its ground state. How can you say that it is a transition element ? (1)
Answer:
Silver can exhibit + 2 O.S. wherein it will have incompletely filled d- orbitals (4d9), hence silver is a transition element.

(iv) Write the structural formula of 1-phenylpentan-1-one. (1)
Answer:
1-Phenylpentan-l-one
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 1

(v) Write the IUPAC name of the given compound. (1)
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 2
Answer:
2,5-dinitrophenol.

(vi) What is meant by reverse osmosis? (1)
Answer:
If a pressure higher than the osmotic pressure is applied in the solution, the solvent will flow from the solution into the pure solvent through the semi-permeable membrane and the process is called reverse-osmosis.

(vii) State the main advantage of molality over molarity as the unit of concentration. (1)
Answer:
Molality does not change with change in temperature while molarity decrease with rise in temperature.

(viii) Explain the following terms with suitable examples: (1)
(a) Frenkel defect
(b) F-centres
Answer:
(a) Frenkel defect: The defect in which the smaller ion/cation is dislocated to a nearby interstitial site. Example: Silver halides, ZnS.
(b) F-centres: The anion vacancy occupied by an electron is called F-centre in alkali metal halides.
Examples: NaCl, KCl, LiCl

Section-B
Short Answer Type Questions:

Question 4.
Differentiate between ‘minerals’ and ‘ores’. (1½)
Answer:
Minerals: These are the combined states of metal in which metal accurs naturally in the earth’s crust. For example : clay, bauxite, mica, dolomite, zinc blende etc.
Ores: The minerals from which a metal can profitably and conveniently extracted is called ores.
All the ores are minerals but all the minerals are not ores.
For example : Bauxite is an ore but clay and mica are not because aluminium metal can be extracted economically of profitably from bauxite not from clay or mica.

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Question 5.
Describe the method for refining nickel. (1½)
Answer:
Mond’s Process : Nickel can be refined by Mond’s process. In this process nickel is first heated with carbon mono oxide at about 330-350 K temperature then it is converted into volatile complex leaving behind non volatile impurities. This volatile complex is further heated at high temperature then it decomposes into pure nickel metal and carbon mono oxide gas.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 3

Question 6.
Define Raoult’s law in its general form in references to solutions. (1½)
Answer:
Raoult’s law: For a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution. Thus, for any component, partial vapour pressure.
P ∝ χ ⇒ P = P°χ
where, p° is the vapour pressure of pure component and χ is the mole fraction of that component.

Question 7.
(a) Based on the nature of intermolecular forces, classify the following solids : Benzene, Silver. (½)
Answer:
Benzene: Molecular solid (non-polar)
Silver: Metallic solid

(b) AgCl shows Frenkel defect while NaCl does not Give reason. (½)
Answer:
Due to intermediate radius of AgCl, the size of Ag+ is smaller than larger Na+ ion of NaCl so it can easily occupy interstitial spaces and shows Frenkel defect.

(c) What type of semiconducfor is formed when Ge is doped with Al? (½)
Answer:
p-type semiconductor is formed when Ge is doped with Al.

Question 8.
(a) For a reaction A + B → Product, the rate law is given by,
Rate = k[A]1[B]2. What is the order of the reaction?
(b) Write the unit of rate constant ‘k’ for the first order reaction. (¾ + ¾ = 1½)
Answer:
(a) The sum of the powers of the concentrations of reactants in the rate law expression is called order of that chemical reaction.
Rate = k[A]1[B]2
Order of reaction = (1 + 2) = 3

(b) Unit of rate constant for first order reaction is s-1 or min-1 or time-1.

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Question 9.
A reaction is of first order with respect to reactant A and of second order with respect to reactant B. How is the rate of this reaction affected when:
(a) the concentration of B alone is increased to three times?
(b) the concentrations of A as well as B are doubled? (¾ + ¾ = 1½)
Answer:
Since, the reaction is of first order w. r. t. A and second order wrt B, then the rate law can be given as, (Rate)1 = k [A][B]2.
(a) When the concentration of B is increased to three times (3B), the fate would be
(Rate)2 = k [A] [3B]2
(Rate)2 = 9k [A] [B]2 = 9 × (Rate)1
∴ Rate is increased by 9 times.

(b) (Rate)3 = k [2A] [2B]2
(Rate)3 = 2 × 2 × 2 × k [A] [B]2
= 8 × (Rate)1
∴ Rate is increased by 8 times.

Question 10.
Write the IUPAC nine of the complex [Cr (NH3)4Cl2]+. What type of Isomerism does It exhibit? (1½)
Answer:
IUPAC name is tetraamminedichlorido chromium (III) ion.
Isomerism: It shows geometrical isomerism and has two isomers as and trans that can be represented as:
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 25

Question 11.
What are transition elements? Write two characteristics of the transition elements. (1½)
Answer:
The elements which lie in between s-and p-block elements in the long form of periodic table belonging to groups 3-12 in which different electrons of d-orbitals are progressively filled in each of the four long periods are called transition elements. Their general electronic configuration is (n – 1)d1-10ns1-2. The general charac-teristics of transition elements are high melting and boiling points paramagnetic behaviour, variable oxidation states, catalytic properties, etc.

Question 12.
Define the term mole fraction. (1½)
Answer:
The mole fraction of a component is the ratio of the number of moles of the component to the total number of moles of all the components present in the solution.
Mole fraction of a component

Number of moles of = \(\frac{\text { the component }}{\text { total number of moles of all the components}}\)
For a binary solution, mole fraction of component A,
χA = \(\frac{n_{\mathrm{A}}}{n_{\mathrm{A}}+n_{\mathrm{B}}}\)
Similarly, for B,
χB = \(\frac{n_{\mathrm{B}}}{n_{\mathrm{A}}+n_{\mathrm{B}}}\)
and
χA + χB = 1

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Question 13.
What is the role of NaOH in the metallurgy of aluminium? (1½)
Answer:
Role of NaOH in the metallurgy of aluminium: The ore of aluminium (bauxite) usually contains SiO2, iron oxides and titanium oxide (TiO2) as impurities. Concentration of bauxite ore is carried out by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar pressure. This way, Al2O3 is leached out as sodium aluminate (and SiO2 too as sodium silicate) leaving behind the impurities.
Al2O3(S) + 2 NaOH(flfl) + 3H2O(2) → 2Na [AI (OH)4](aq)

Question 14.
Which is a stronger reducing agent Cr2+ or Fe2+and why? (1½)
Answer:
Cr2+is stronger reducing agent than Fe2+.
Reason: In case of Cr2+, the configuration changes from d4 to d3 and it is oxidised, into Cr3+. It is due to extra stability of (t2g)3 configuration.
But in case of Fe2+ ion, the configuration changes from d6 to d5 and it changes into Fe3+ ion.
(Note : In aqueous medium, d3 configuration is more stable as compared to d5 configuration.)

Question 15.
Write down the IUPAC name of the complex [Pt (en)2Cl2]2+. What type of isomerism is shown by this complex? (1½)
Answer:
IUPAC name of [Pt (en)2Cl2]2+ is dichlorobis (ethane 1, 2-diamine) platinum (IV) ion. The given complex shows geometrical isomerism and optical-isomerism as follows.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 4

Section-C
Long Answer Type Questions

Question 16.
With the help of diagram, explain the role of activated complex in a reaction. (3)
Or
Mention the factors that affect the rate of a chemical reaction. (3)
Answer:
When the colliding molecules possess the kinetic energy less than the threshold Energy (Et), they require the energy to achieve Et. This amount of energy (energy required) is known as activation energy (Ea). After achieving the activation energy (i.e. Ea), they reach to an activated stage. This stage is different from the reactant as well as from the product, e.g. in the reaction between H2(g) and I2(g), activated complex has configuration in which H – H and I – I bonds are breaking and H-I bonds are forming as shown below:
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 5
Potential energy diagram of this action is shown below
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 6

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Question 17.
Out of C6H5CH2Cl and C6H5CH(Cl)C6H5 which is more easily hydrolysed by aqueous KOH?
Or
p-Dichlorobenzene has higher melting point and lower solubility than those of o- and m- isomers. Discuss. (3)
Answer:
C6H5CH2Cl is a primary (1°) aralkyl halide while. C6H5CH(Cl)C6H5 is a secondary (2°) aralkyl halide.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 7
In SN1 reactions, the reactivity depends upon the stability of carbocations. Since the carbocation
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 8
C6H5 gets hydrolysed more easily than C6H5CH2Cl under SN1 conditions.

Question 18.
(a) Give chemical tests to distinguish between the following pairs of compounds:
(i) Ethanal and Propanal
(ii) Phenol and Benzoic acid
(b) How will you bring about the following conversions ?
(i) Benzoic acid to benzaldehyde
(ii) Ethanal to but-2-enal
(iii) Propanone to propene
Give complete reaction in each case. (4)
Or
(a) How will you bring about the following conversions:
(i) Ethanol to 3-hydroxybutanal
(ii) Benzaldehyde to Benzophenone
(b) An organic compound A has the molecular formula C8H1602. It gets hydrolysed with dilute sulphuric acid and gives a carboxylic acid B and an alcohol C. Oxidation of C with chromic acid also produces, B. C on dehydration reaction gives but-l-ene. Write equations for the reactions involved. (4)
Answer:
(a) (i) Ethanal and Propanal: Ethanal and propanal can be distinguished by iodoform test. Warm each compound with iodine and sodium hydroxide solution in water. Ethanal gives yellow crystals of iodoform while propanal does not respond to iodoform test.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 9

(ii) Phenol and Benzoic acid : On addition of NaHCO3 to both solutions, carbon dioxide gas is evolved with benzoic acid while phenol does not form CO2.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 10

(b) (i) Benzoic add to benzaldehyde:
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 11

(ii) Ethanal to but-2-enal
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 12

(iii) Propanone to propene
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 13

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Section-D
Essay Type Questions:

Question 19.
Explain the mechanism of the following reactions:
(a) Addition of Grignard’s reagent to the carbonyl group of a compound forming an adduct followed by hydrolysis.
(b) Acid catalysed dehydration of an alcohol forming an alkene.
(c) Acid catalysed hydration of an alkene forming an alcohol. (4)
Or
How are the following conversions carried out?
(a) Propene to propan-2-ol
(b) Benzly chloride to Benzyl alcohol
(c) Anisole top-Bromoanisole. (4)
Answer:
(a) Carbonyl group undergoes nucleophilic addition reaction with Grignard reagent to form an adduct which undergoes hydrolysis to give alcohol in the following manner:
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 14

(b) The mechanism of dehydration of ethanol involves the following steps:
Mechanism: It involves the following three step:
Step 1 : Formation of protonated alcohol H H
H-C-C-O-H+H
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 15

Step 2: Formation of Carbocation: It is the slowest and rate determining step.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 16

Step 3: Formation ofethene by elimination of a proton
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 17

(c) Acid catalysed hydration: Alkenes react with water in the presence of acid as catalyst to form alcohols.
Mechanism: It involves the following three steps:
Step 1: Protonation of alkene to from carbocation by electrophilic attack of
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 18

Step 2: Nucleophilic attack of water on carbocation
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 19

Step 3: Deprotonation to form an alcohol
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 20

RBSE 12th Chemistry Model Paper Set 8 with Answers in English

Question 20.
Write chemical equations for the following conversions:
(a) Nitrobenzene to benzoic acid.
(b) Benzyl chloride to 2-phenylethanamine
(c) Aniline to benzyl alcohol. (4)
Or
Give the structure of A, B and C in the following reactions:
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 21
Answer:
(a) Nitrobenzene to benzoic acid.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 22

(b) Benzyl chloride to 2-phenylethanamine
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 23

(c) Aniline to benzyl alcohol.
RBSE 12th Chemistry Model Paper Set 8 with Answers in English 24

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