Sunday, March 23, 2008

Chemistry Sample CBSE Examination Paper Class XII


Time Allowed : 3 Hours Maximum Marks : 70

All questions are compulsory.
Marks for each question are indicated against it.
Question numbers 1 to 5 are very short answer question, each of 1 mark. Answer these in one world or about one sentence each.
Question numbers 6 to 12 are short answer questions of 2 marks each of one mark. Answer these in about 30 words each.
Questions number 13 to 24 are short answer questions of 3 marks each. Answer these in about 40 words each.
Question numbers 25 to 27 are long answer questions of 5 marks each. Answer these in about 70 words each.
Use log tables if necessary. Calculators are not permitted.

How many effective sodium ions are located at the centres of faces of a unit cell in a sodium chloride crystal?
A reaction:
Reactant > product is represented by


The order of the reaction in this case
What does the slope of the following reaction
Propose the mechanism for the following reaction:

Write the IUPAC name of the compound.

Carefully examine the diagram and name the process involved:

Identify the type of inter molecular forces that exist between the following pairs:
(i) Na+ ion and water molecules
(ii) Ag+ ion and I- ion
(iii) Argon and Argon
(iv) HF and H2O
Predict the entrophy change (Positive/Negative) in the following:
(i) A liquid substance crystallizes into a solid
(ii) Temperature of crystal is increased.
(iii) CaCO3(s) > CaO(s) + CO2(g)
(iv) N2 (1 atm) (g) > N2 (0.5 atm) (g)
How is [(CH3)2 SiO]n prepared? Write its two applications.
What is a stereospecific reaction? Give one example of this reaction.
Identify A, B, C, and D in the following reactions.


Write the reactions and conditions involved in the following conversions?

Acetic acid into ethy alcohol
Cumene into phenol
The presence of benzoquinone inhibits the free radical polymerization of a Vinyl derivative”. Explain.
What are anomers? How many anomers of glucose are known? Name them.
(a) Calculate the energy of photon which is necessary to raise an electron in hydrogen atom from n=1 to n=3 energy level? (Given the ionization energy of hydrogen atom is 1.312 ×103 kJ mol-1and NA=6.02 × 1023 mol-1).
(b) Which of the following excitations required maximum energy?

n1 >n2
n2 >n3
n3 >n4
or all require the same energy.


Suppose the velocities of an electron and a rifle bullet of mass 0.03 kg are each measured with an uncertainity of v =10-3 m s-1 calculate the minimum uncertainities in their positions. (Given: mass of an electron =9,1 x 10-31 kg)
Comment on the calculated values of uncertainities in positions in the two cases.
Explain the following terms with suitable examples:

n-type semiconductor
forbidden zone
The Henry law constant for oxygen dissolved in water is 4.34 × 104 atm at 250C. If the partial pressure of oxygen in air is 0.2 atm. Under ordinary atmospheric conditions. Calculate the concentration (in moles per litre) of dissolved oxygen in water in equilibrium with air at 250C.
At elevated temperatures, HI decomposes according to the chemical equation:
2HI (g) >H2 (g) + I2 (g)
at 4430C. The rate of the reaction increases with concentration of HI, as shown in the following table:
1 2 3
HI (mol L-1)
Rate (mol L-1 s-1) 0.005
7.5 × 10-4
3.0 × 10-3
1.2 × 10-2

(a) Determine (i) order of this reaction and (ii) write the rate expression.
(b) Calculate the rate constant and give its units.
(a) Among the iron complexes, K3 [Fe(CN)6] shows very low parqamagnetism where as K3[FeF6] is highly paramagnetic explain.
(b) Define crystal field orbital splitting energy.
( c ) Write the shape of Fe(CO)5 molecule.
Represent the following using a nuclear equation of each:
Production of C-14 in nature
Write chemical tests to distinguish the following pair of compounds:

(b) Write a chemical equation examplifying Clemmensen reduction.
Give reasons of the following:
The basic strength of aliphatic amines in solution is in the order sec.> tert. > primary.
Nitro compounds have higher boiling than hydrocarbons having nearly same molecular mass.
(b) By giving an example describe carbylamine reaction.
(a) Which bonds in the back bone of a peptide can rotate freely and which cannot? Give reasons.
(b) Write one difference between parallel and antiparallel b pleated sheets. Give one example of parallel pleated sheet.
Answer the following :
(a) An unknown fibre (A) is stronger than steel, stiffer than titanium an lighter than aluminium.
What could the fibre (A) be?
(b) Why are liquid propellants favoured over solid propellants?
(c) What type of medicines are omeprazole and Lansoprazole?
The change in entropy with respect to temperature in case of a sample is graphically represented below:

Carefully analyse the graph and answer the following:
(i) What does T1 and T2 indicate?
(ii) What does AB curve show?
(iii) What does BC curve show? Why temperature does not change?

Describe the following giving one example each:
(a) Mechanism of heterogeneous catalysis.
(b) Hardy Schulze Rule
(a) Write the reactions occurring during the electrodes of.

Sulphuric acid at the anode
Aqueous Silver nitrate solution using silver electrodes.
Aqueous sodium chloride solution.
Write the anodic and cathodic reactions involved during the discharging of lead storage battery.
How many Faraday’s of electric charge is involved per mole of H2SO4 consumed, when the lead storage battery is in use?

(a) In the Leclanche cell write the following:

The chemical equations involved at the cathode.
Change in the Oxidation state of Mn.
The complex entity formed between Zn2+ (aq) and NH3 (g).

(b) In a hydrogen - oxygen fuel cell write the reactions involved at the anode and the cathode.
(c) How will the value of Ecell change in an electrochemical cell involving the following reaction if the concentration of Ag+ (aq) is increased?

Mg(s) + 2Ag+ (aq) > Mg2+ (aq)+ Ag (s)

(d) Why is mercury cell used in hearing aids?
(a) Identify the species from A to D in the extraction of silver from its ore (A)

(b) Give reasons for the following:

With d4 configuration Cr2+ is reducing where as Mn3+ is oxidizing.
Interstitial compounds are well known for transition metals.
The highest oxidation state of a metal is exhibited is exhibited in oxides and fluorides.
Account for the following:

All the bonds in PCI5 are not equivalent
Sulphur in vapour state exhibits paramagnetism
Fluorine is the strongest oxidant amongst the halogens.
Among the noble gases, only xenon is known to form true chemical compounds.
PbO2 is a stronger oxidizing agent than SnO2.

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