Students can use CBSE Previous Year Question Papers Class 12 Chemistry with Solutions and CBSE Class 12 Chemistry Question Paper 2016 Comptt (Outside Delhi) to familiarize themselves with the exam format and marking scheme.
CBSE Class 12 Chemistry Question Paper 2016 Comptt (Outside Delhi) with Solutions
Time allowed : 3 hours
Maximum marks : 70
General Instructions :
(i) All questions are compulsory.
(ii) Q.no. 1 to 5 are very short answer questions and carry 1 mark each.
(iii) Q.no. 6 to 10 are short answer questions and carry 2 marks each.
(iv) Q.no. 11 to 22 are also short answer questions and carry 3 marks each.
(v) Q.no. 23 is a value based question and carries 4 marks.[*]
(vi) Q.no. 24 to 26 are long answer questions and carry 5 marks each.
(vii) Use log tables if necessary. Use of calculators is not allowed.
Deleted from Syllabus.
Question 1.
Define rate constant (k). [1]
Answer:
Rate constant : It is defined as the rate of reaction when the concentration of reactants is taken as unity.
Question 2.
Why is Tyndall effect shown by colloidal solutions? [1]
Answer:
It is so due to large size of colloidal particles. In colloidal solutions particle size of dispersed phase is comparable to the wavelength of light used.
Question 3.
Write the IUPAC name of the following coordination compound [NiCl
4
]
2
-. [1]
Answer:
Tetrachloridonickelate (II) ion.
Question 4.
Out of CH
3
OH and
is more acidic ?
Answer:
is more acidic, as Phenoxide ion formed is more stabilized by Resonance.
Question 5.
What are Associated Colloids? Given an example. [1]
Answer:
Colloids which act as electrolyte at low concentration and show colloidal behaviour at high concentration are called Associated colloids.
Example : Soap solution, Detergents.
Question 6.
Explain the following terms with suitable examples : [2]
(i) Frenkel defect (ii) F-centres
Answer:
(i) Frenkel defect : The defect in which the smaller ion/cation is dislocated to a nearby interstitial site.
Example : Silver halides, ZnS.
(ii) F-centres : The anion vacancy occupied by an electron is called F-centre in Alkali metal halides.
Example ; NaCl, KCl, LiCl.
Question 7.
Define osmotic pressure. How is osmotic pressure related to the concentration of a solute in a solution? [2]
Answer:
Osmotic pressure is the measure of excess pressure applied on solution side to stop the process of osmosis. Osmotic pressure is directly proportional to the conentration of solute in solution
π a C
Question 8.
What happens when : [2]
(i) Concentrated H
2
SO
4
is added to calcium fluoride?
(ii) SO
3
is passed through water?
Answer:
(i) Cone. H
2
SO
4
reacts with CaF
2
giving Hydrogen Fluoride
CaF 2 + H 2 SO 4 → CaS0 4 + 2HF
(ii) SO 3 passed in water giving Sulphuric Acid
SO 3 + H 2 O → H 2 SO 4
Question 9.
Give reasons :
(i) Zn is not regarded as a transition element.
(ii) CH
2+
is a strong reducing agent.
Answer:
(i) Zinc Atomic no. 30 have EC 3d
10
, 4s
2
. It has completely filled ‘d’ orbitals.
(ii) Cr
+2
(3d
4
) after loosing one electron forms Cr
+3
(d
3
). It has tigeg configuration. Hence more stable. Hence Cr+2 acts as reducing agent.
Or
Cr +3 is more stable than Cr +2 , therefore Cr +2 looses one electron. Hence acting as strong reducing agent.
Question 10.
Write the equations for the preparation of 1-bromobutane from : [2]
(i) 1-butanol (ii) but-1-ene
Answer:
(i) Preparation of 1-bromobutane from 1-butanol
(ii) Preparation of 1-bromobutane from but-1-ene
Or
Which compound in each of the following pairs will react faster in S
N
2 reaction with -OH?
(i) CH
3
Br or CH
3
I
(ii) (CH
3
)
3
CCl and CH
3
Cl
Answer:
(i) CH
3
I : Because Iodide is better leaving group than bromide.
(ii) CH
3
Cl : Carbon atom leaving group is less hindered.
+Question 11.
Silver crystallises in f.c.c. lattice. If edge length of the cell is 4.07 × 10
-8
cm and density is 10.5 g cm
-3
, calculate the atomic mass of silver. [3]
Answer:
Question 12.
An aqueous solution of 2 percent non-volatile solute exerts a pressure of 1.004 bar at the boiling point of the solvent. What is the molecular mass of the solute?
[Vapour pressure of water = 1.013 bar] [3]
Answer:
Question 13.
The rates of most reactions double when their temperature is raised from 298 K to 308 K. Calculate their activation energy.
[R = 8.314 JK
-1
mol
-1
] 3
Answer:
Question 14.
Explain the following terms : [3]
(i) Peptization
(ii) Lyophobic colloids
(iii) Dialysis
Answer:
(i) Peptization : The conversion of freshly prepared ppt into colloidal solution by shaking with disperson medium containing small amount of electrolyte.
(ii) Lyophobic colloids : Solvent hating colloids are called lyophobic colloids. For example, Gold sol.
(iii) Dialysis : It is the process of removing a dissolved substance from a colloidal solution by means of diffusion through a membrane.
Question 15.
Outline the principles of refining of metals by the following methods : [3]
(i) Zone refining
(ii) Electrolytic refining
(iii) Vapour phase refining
Answer:
(i) Zone refining : Impurities are more soluble in the melt than element.
(ii) Electrolytic refining: More basic metal forms ions and are deposited on the cathode by passing electricity.
(iii) Vapour phase refining : Pure metal forms volatile compound with suitable reagent and the volatile compound is decomposed to give pure metal.
Question 16.
Describe the preparation of potassium permangnate. How does the acidified permanganate solution react with oxalic acid? [3]
Answer:
Pyrolusite ore is digested in KOH in the presence of oxygen
2MnO
2
+ 4KOH + O
2
→ 2K
2
MnO
4
+ 2H
2
O
3MnO
4
2-
+ 4H
+
→ 2MnO
4
–
+ MnO
2
+ 2H
2
O
Reaction with oxalic acid in Acidic medium ,
5C 2 O 4 2- + 2MnO 4 – + 16H + → 2Mn 2+ + 8H 2 O + 10CO 2
Or
Define lanthanoid contraction. Write its two consequences.
Answer:
Steady and regular decrease in atomic or ionic size with increasing atomic no. in Lanthanoid series. Consequences :
(i) Due to lanthanoid contraction elements of 4d and 5d have similar size, hence occurs together.
(ii) Basic character of trivalent hydroxide decreases.
Question 17.
Write the hybridization, shape and magnetic character of [Fe(CN)
6
]
4-
. [3]
Answer:
Hybridisation : d2sp3 Shape : Octahedral
Magnetic character : Diamagnetic as all the electrons get paired due to strong field ligand CN-.
Question 18.
What happens when [3]
(i) CH
3
-Cl is treated with aqueous KOH?
(ii) CH
3
-Cl is treated with KCN?
(iii) CH
3
-Br is treated with Mg in the presence of dry ether?
Answer:
Question 19.
Explain the following with an example in each : [3]
(i) Kolbe’s reaction
(ii) Reimer-Tiemann reaction
(iii) Williamson ether synthesis
Answer:
(i) Kolbe’s reaction : Phenol reacts with CO
2
at 390-400 K under pressure 4-7 giving Selicyle Acid
(ii) Reimer-Tiemann reaction : Phenol reacts with CHCl
3
and NaOH at 340 K giving salicyl aldehyde.
(iii) Williamson ether synthesis : Alkyl Halide reacts with Alkoxide.
Question 20.
Write the products A and B in the following :
Answer:
Question 21
Write two uses of each of the following polymers. [3]
(i) Polyproplene
(ii) PVC
(iii) Nylon-6,6
Answer:
(i) Polypropylene : Manufacture of ropes, toys, pipes etc.
(ii) PVC : Manufacture of raincoats, handbags, vinyl flooring, water pipes etc.
(iii) Nylon-66 : Manufacture of sheets, bristles from brushes, textiles etc.
Question 22.
What are enzymes? Describe their functions. Name two diseases which are caused due to deficiency of enzymes. [3]
Answer:
Enzymes are protein molecules which acts catalyst in Biochemical Reactions (biocatalyst). They increase the rate of biochemical reactions. For example : Zymase, Invertase etc.
Two diseases due to deficiency of enzymes are : Anemia, Gaucher’s disease.
Question 23.
Ankit’s grandfather is not only obese but he is also a diabetic patient. Seeing his fondness for sweets, Ankit suggested him to replace sugar with artificial sweeteners. After few days, Ankit observed a controlled level of sugar in his grandfather.
Answer the following:[4]
*(i) What are the values displayed by Ankit?
(ii) What are artificial sweeteners?
(iii) Give two examples of artificial sweeteners.
(iv) Name an artificial sweetener which is unstable at cooking temperature.
Answer:
(i) As per latest CBSE curriculum, Value Based Questions will not be asked in the examination.
(ii) Compounds which are used as a substitute of sugar due to its low calorie intake.
(iii) Examples of Artificial Sweeteners : Sucyalose/ Aspartame /lAlitame
(iv) Aspartame
Question 24.
(a) What are the two classifications of batteries? What is the difference between them?
(b) The resistance of 0.01 M NaCl solution at 25°C is 200 Q. The cell constant of the conductivity cell is unity. Calculate the molar conductivity of the solution. [5]
Answer:
(a) Two types of batteries are Primary batteries and Secondary batteries. Primary batteries are non-chargeable whereas secondary batteries are rechargeable.
(b)
Or
What are fuel cells? Give an example of a fuel cell.
Calculate the equilibrium constant (log K
c
) and ∆
r
G° for the following reaction at 298 K.
Given \(\) = 0.46 V and IF = 96500 C mol
-1
Answer:
(a) Cell which converts energy of combustion of fuel directly into electricity.
Example : H
2
-O
2
fuel cell.
Or
Those cells which convert fuel energy directly into electrical energy.
Example : H
2
-O
2
fuel cell
(b)
Question 25.
(a) Draw the structure of
(i) BrF
3
(ii) XeOF
4
(b) Explain giving reason in each case:
(i) Why H
2
Te is more acidic than H
2
S?
(ii) Why are halogens strong oxidising agnets?
(iii) Why does nitrogen show catenation tendency less than phosphorus?
Answer:
(a)
(b) (i) Because of low bond dissociation enthalpy of H-Te bond as Te has larger size than S.
(ii) Because of their strong electron affinity they have seven valence electrons.
(iii) Because N-N single bond is weaker than P-P single bond.
Or
(a) (i) Why PCl
5
gives fumes in moisture?
(ii) Why Interhalogens are more reactive than pure halogens?
(b) Draw the structures of the following :
(i) PCl
5
(s) (ii) H
0
S
0
O
8
(iii) XeF
4
Answer:
(a) (i) Because it reacts with moisture present in the air giving HQ.
(ii) Because of low bond dissociation enthalpy of interhalogens.
(b) (i) [PCl
4
]
+
[PCl
6
]
Question 26.
(a) Complete the following equations :
(b) Distinguish between :
Answer:
(a) (i) Cannizzaro reaction
(b) (i) On adding NaHCO
3
, CH
3
COOH produces brisk effervescence of CO
2
gas whereas phenol does not.
(ii) On heating with Tollen’s reagent, CH
3
CHO forms silver mirror whereas CH
3
COCH
3
does not.
Or
(a) What is meant by the following terms? Give an example of the reaction in each case.
(i) Aldol (ii) Semicarbazone
(b) Complete the following :
Answer:
(a) (i) Two molecules of aldehyde and ketones containing a-hydrogen atom react in the presence of aqueous alkali giving product known as Aldol.
Example :
(ii) Aldehyde and ketones react with semicarbazide giving product called semicarbazone.
(b)
