CBSE Sample Papers for Class 12 Chemistry Solved 2016 Set 4
Section A
1. What is rectified spirit?
2.How is urotropine prepared? Mention a use of it.
3.Among the four bases present in DNA, which is not present in RNA?
4.Complete the following reaction.
5.Haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reactions, why? Give only one reason.
Section B
6.(i) What is meant by molality of the solution? (ii) State Raoult’s law for volatile liquids.
7.Perovskite, a mineral containing calcium, oxygen and titanium, crystallises in the given unit cell as shown below.
On the basis of above information, answer the following questions.
(i)What is the formula of perovskite?
(ii)What is the oxidation state of titanium in the given lattice
8.(i) Write the balanced chemical equation of the reaction in which KMn04 acts as an oxidising agent in the acidic medium.
(ii) La(OH)3 is more basic than Lu(OH)3, why?
9.Express the relation among cell constant, resistance of the solution in the cell and conductivity of the solution.How is molar conductivity of a solution related to its conductivity?
Or
The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9 Scm2 mol-1
10.Explain the following terms.
(i) F-centres
(ii)Schottky defect
Section C
11.(i) Why is froth floatation method selected for the concentration of sulphide ores?
(ii) One ore is a mixed sulphide of lead and zinc (PbS-ZnS). Suggest a method to separate the mixture
12.(i) Draw the structure of ozone molecule.
(ii) (a) Draw the structure of H3Po4 ,(HPO3)3 .
(b) Does the hydrolysis of XeF6 lead to a redox reaction?
14.Discuss the mechanism of SN1 reaction of haloalkanes
15.Henry’s law constant for CO 2 dissolving in water is 1.67 xlO8 Pa at 298 K. Calculate the quantity of C02 in 1 L of soda water when packed under 2.5 atm C02 pressure at 298 K.
16.What is a nickel-cadmium cell? State its one merit and one demerit over lead storage cell. Write the overall reaction that takes place during discharging (use) of this cell. What is the value exhibited in the choice of decision?
17.Compare the stability of +2 oxidation state for the elements of the first transition series [Sc= 21 to Cu= 29].
18.Write the name, structure and the magnetic behaviour of each one of the following complexes.
(i)[Pt (NH3)2Cl(N02)]
(ii)[Co(NH3 )4 C12]C1 (iii) [Ni(CO)4 ] [Atomic number of Co= 27, Ni= 28, Pt= 78 ]
19.Draw the structure and name the product formed, if the following alcohols are oxidised. Assume that an excess of oxidising agent is used.
(i)CH3CH2CH2CH2OH
(ii)2-butanol (iii) 2-methyl-1-propanol
20.Define the following giving one example of each
(i) Zwitter ion (ii) Glycosidic linkage
21.Write the name of monomers and structures of the following polymers.
(i) Buna-S (ii) Dacron (iii) Glyptal
22.What are analgesic medicines? How are they classified and when are they commonly recommended for use?
Or
(i)What are antipyretic medicines?
(ii)Name any one of them.
(iii)Can it play any other role also?
23.Anu’s teacher was explaining Modern Adsorption Theory of catalysis in a slide-based lecture. By chance he could not place numbering on slides. She was asked to help to place the slides in the order of the steps involved.
Based on the above figures, answer the following questions.
(i)Arrange these slides in accordance with correct steps.
(ii)Give one example of industrial application involving this theory.
(iii)What values are associated with Anu?
Section E
24.An acid A C8H602Br on bromination in the presence of FeBr3 gives two isomers B and C of the formula C8H602Br2.
Vigorous oxidation of A, B and C gives acids D, E and F, respectively. The acid D, C7H502Br is the strongest acid among all the isomers whereas E and F each has molecular formula of C7H402Br2. Give structures of A to F with justification.
Or
An aldehyde A (C11HsO) which does not undergo self aldol condensation gives benzaldehyde and two moles of B on ozonolysis. Compound B on oxidation with silver ions gives oxalic acid. Identify the compound A and B.
25.(i) Explain the Ostwald’s process for the manufacture of nitric acid.
(ii)Write the balanced equations for the reactions when nitric acid reacts with
(a)I2 (b) C
(c)S8 (d) P4
(iii)Nitrous acid acts as both oxidising and reducing agent but nitric acid acts only as oxidising agent. Why?
Or
(i)How is sulphur dioxide prepared in
(a)laboratory?
(b)industry?
(ii)What happens when sulphur dioxide is passed through water and reacts with sodium hydroxide? Write the balanced equation.
Answers
Section A
1. What is rectified spirit?
Ans.A mixture of 95% ethyl alcohol and 5% water is called rectified spirit.
2.How is urotropine prepared? Mention a use of it.
Ans.Hexamethylene tetraamine is called urotropine. It is prepared by the reaction of methanal (HCHO) with ammonia (NH3).
Use It is used as an antiseptic for urinary tract infections.
3.Among the four bases present in DNA, which is not present in RNA?
Ans.The four bases present in DNA are
(i) Adenine (A) (ii) Guanine (G) (iii) Thymine (T) (iv) Cytosine (C)
4.Complete the following reaction.
5.Haloarenes are much less reactive than haloalkanes towards nucleophilic substitution reactions, why? Give only one reason.
Ans.Haloarenes are less reactive than haloalkanes towards nucleophilic substitution reactions due to the delocalisation of lone pairs of electrons of halogen atoms with n- electrons of the benzene ring. There is partial double bond character in C—X bond. Thus, C—X bond cleavage in haloarenes are difficult as compared to that in the haloalkanes.
Section B
6.(i) What is meant by molality of the solution? (ii) State Raoult’s law for volatile liquids.
Ans.(i) Molality is defined as the number of moles of the solute per kilogram of the solvent. It is represented by m.
(ii) Raoult’s law (for the solution of volatile liquids) states that the partial vapour pressure of each component of the solution is directly proportional to its mole fraction. Thus, for any component, partial vapour pressure, p propositional to x; p = p0 x, where, p° is the vapour pressure of the pure component and % is the mole fraction of that component.
7.Perovskite, a mineral containing calcium, oxygen and titanium, crystallises in the given unit cell as shown below.
On the basis of above information, answer the following questions.
(i)What is the formula of perovskite?
(ii)What is the oxidation state of titanium in the given lattice
Ans.
8.(i) Write the balanced chemical equation of the reaction in which KMn04 acts as an oxidising agent in the acidic medium.
(ii) La(OH)3 is more basic than Lu(OH)3, why?
Ans.
9.Express the relation among cell constant, resistance of the solution in the cell and conductivity of the solution.How is molar conductivity of a solution related to its conductivity?
Or
The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9 Scm2 mol-1
Ans. The resistence (R) of a conductor varies directly with length (l) and inversely with area of cross-section
10.Explain the following terms.
(i) F-centres
(ii)Schottky defect
Ans.(i) F-centres The anionic sites occupied by unpaired electrons are called F-centres or colour centres. The crystal becomes coloured due to the excitation of these unpaired electrons when they absorb energy from the visible light falling on the crystals. For example, LiCI (Lithium Chloride) crystal appears pink due to the excess of lithium.
(ii) Schottky defect This defect is shown by those ionic substances in which the cation and anion are of almost similar size, e.g. NaCI, KCI, CsCI and AgBr show this type of defect.
It is basically a vacancy defect. In this type of defect, equal number of cations and anions are found missing from their lattice sites. Schottky defect decreases density of the substance
Section C
11.(i) Why is froth floatation method selected for the concentration of sulphide ores?
(ii) One ore is a mixed sulphide of lead and zinc (PbS-ZnS). Suggest a method to separate the mixture
Ans.(i) The froth floatation method is selected for the concentration of sulphide ores because sulphide ores are wetted preferentially by pine oil and impurities (gangue) are wetted by water. Hence, sulphide ore forms froth. Thus, become lighter and rise to the surface while gangue particles being heavier settle at the bottom. In this way, sulphide ore particles can be separated easily from gangue particles.
(ii) PbS and ZnS both form froth with pine oil on bubbling air inside the mixture. In such case, NaCN is used as a depressant.Before froth floatation process is used, NaCN is mixed (as a depressant) which forms a complex with ZnS.
ZnS + 4NaCN ——- > Na2[Zn(CN)4] + Na2S
PbS remains insoluble and is separated. CuS04 is then added to activate depressed ZnS and air is blown when ZnS floats. This method is called differential floatation.
12.(i) Draw the structure of ozone molecule.
(ii) (a) Draw the structure of H3Po4 ,(HPO3)3 .
(b) Does the hydrolysis of XeF6 lead to a redox reaction?
Ans.
Ans.
14.Discuss the mechanism of SN1 reaction of haloalkanes
Ans.The substitution reactions where rate depends only upon the concentration of one reactant, are called SN1 reactions. These reactions are generally carried out in polar protic solvents (like water, alcohol, acetic acid, etc.). The reaction between tertiary butyl bromide and hydroxide ion yields tertiary butyl alcohol and follows the first order kinetics
15.Henry’s law constant for CO 2 dissolving in water is 1.67 xlO8 Pa at 298 K. Calculate the quantity of C02 in 1 L of soda water when packed under 2.5 atm C02 pressure at 298 K.
16.What is a nickel-cadmium cell? State its one merit and one demerit over lead storage cell. Write the overall reaction that takes place during discharging (use) of this cell. What is the value exhibited in the choice of decision?
17.Compare the stability of +2 oxidation state for the elements of the first transition series [Sc= 21 to Cu= 29].
Ans.In the first transition series, the stability of +2 oxidation state decreases from Sc to Cu. This is because of the increase in the sum of first and second ionisation energies.
However, the +2 state of Mn, Ni and Zn is highly stable because of the presence of half-filled and fully filled orbitals in Mn2+ and Zn2+ respectively. The stability of Ni2+ is due to its highly negative heat of hydration.
18.Write the name, structure and the magnetic behaviour of each one of the following complexes.
(i)[Pt (NH3)2Cl(N02)]
(ii)[Co(NH3 )4 C12]C1 (iii) [Ni(CO)4 ] [Atomic number of Co= 27, Ni= 28, Pt= 78 ]
Ans.
19.Draw the structure and name the product formed, if the following alcohols are oxidised. Assume that an excess of oxidising agent is used.
(i)CH3CH2CH2CH2OH
(ii)2-butanol (iii) 2-methyl-1-propanol
Ans.
20.Define the following giving one example of each
(i) Zwitter ion (ii) Glycosidic linkage
Ans.
21.Write the name of monomers and structures of the following polymers.
(i) Buna-S (ii) Dacron (iii) Glyptal
Ans.
22.What are analgesic medicines? How are they classified and when are they commonly recommended for use?
Or
(i)What are antipyretic medicines?
(ii)Name any one of them.
(iii)Can it play any other role also?
Ans.The chemical substances which are used to relieve pain are called analgesic medicines.
These are of two types
(i)Non-narcotic drugs These are non-habit forming and effective in relieving or preventing heart attack, skeletal pain of viral inflammation, etc.
(ii)Narcotic drugs These drugs produce sleep, unconsciousness and convulsions. These are habit forming drugs and are recommended for the relief in post operative pain, cardiac pain and terminal cancer.
Or
(i)Medicines used to lower the temperature of the body in case of high fever are called antipyretic medicines.
(ii)Paracetamol
(iii)They can also play the role of analgesics, i.e. relieve the body pains.
23.Anu’s teacher was explaining Modern Adsorption Theory of catalysis in a slide-based lecture. By chance he could not place numbering on slides. She was asked to help to place the slides in the order of the steps involved.
Based on the above figures, answer the following questions.
(i)Arrange these slides in accordance with correct steps.
(ii)Give one example of industrial application involving this theory.
(iii)What values are associated with Anu?
Ans.
Section E
24.An acid A C8H602Br on bromination in the presence of FeBr3 gives two isomers B and C of the formula C8H602Br2.
Vigorous oxidation of A, B and C gives acids D, E and F, respectively. The acid D, C7H502Br is the strongest acid among all the isomers whereas E and F each has molecular formula of C7H402Br2. Give structures of A to F with justification.
Or
An aldehyde A (C11HsO) which does not undergo self aldol condensation gives benzaldehyde and two moles of B on ozonolysis. Compound B on oxidation with silver ions gives oxalic acid. Identify the compound A and B.
Ans.The acid A has a COOH group and a Br-atom. As on bromination, it gives two isomeric dibromo derivatives, the two groups in the aromatic acid A must be at the ortho positions.
25.(i) Explain the Ostwald’s process for the manufacture of nitric acid.
(ii)Write the balanced equations for the reactions when nitric acid reacts with
(a)I2 (b) C
(c)S8 (d) P4
(iii)Nitrous acid acts as both oxidising and reducing agent but nitric acid acts only as oxidising agent. Why?
Or
(i)How is sulphur dioxide prepared in
(a)laboratory?
(b)industry?
(ii)What happens when sulphur dioxide is passed through water and reacts with sodium hydroxide? Write the balanced equation.
Ans.
Ans.
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