|
Chemistry Class - XII 1997
(CBSE)
You are on questions 21 to 34 of Set I
Q.21 Explain the mechanism of the
acid-catalysed dehydration of ethanol at high temperature. (2
marks)
Q.22 Comment on the structural difference
between thermoplastics and thermosetting polymers. (2 marks)
Q.23 What are micels? Given an example of a
micellar system. (2 marks)
Q.24 Consider the given standard potentials
(in volts)in 1 M acidic solution :
Fe2+/Fe, -0.4 V ;
Fe3+/Fe2+, +0.8 V
Mn2+/Mn, -1.2 V ;
Mn3+/Mn2+, +1.5 V
(i) Comment on the relative
stabilities of +2 and +3 oxidation states of iron and manganese;
(ii)
Which of the two metals may be more easily oxidised to +2 state?
(2
marks)
Q.25 Account for the following statements : (2
marks)
(i) Co(II) is stable in aqueous solution but in the presence of
strong ligands and air it can get oxidised to Co(III). (Atomic number
Co=27)
(ii) One among the lanthanide's,Ce(III) can be easily oxidised
to Ce(IV). (Atomic No : Ce=58).
Q.26 Write an equation in ionic form to
represent the oxidising action of Cr2O2-7
in acidic medium. Also draw the structure of
Cr2O2-7. (2 marks)
Q.27 An element of atomic mass 98.5g
mol-1 occurs in fcc structure. If its unit cell edge length is
500pm and its density is 5.22g cm-3, what is the value of
Avagadro Constant? (3 marks)
Q.28 One litre aqueous solution of sucrose
(molar mass=342g mol-1) weighing 1015g is found to record an
osmotic pressure of 4.82 atom at 293k. What is the molarity of the sucrose
solution? (R=0.0821 atom mol-1K-1)
(3
marks)
Q.29 Calculate the potential of the
following cell reaction at 298K :
Sn4+(1.50M) + Zn(s)
---> Sn2+(0.50M) + Zn2+(2.0M)
The standard
potential Eo of the cell is 0.89 V. Whether the potential of
the cell will increase or decrease, if the concentration of
Sn4+ is increased in the cell? (R = 8.314JK-1
mol-1; F=96,500 C mol-1) (3 marks)
Q.30 (a) How many
b
-particles are emitted in the decay series :
238
U92 ---> 206 Pb82 ?
(b)
Complete the following nuclear reaction :
(i)2713
Al + 42 H --> 3015 Pb +
.....
(ii)23592 U + 10n
--> 14056+.....+ 210n (3
marks)
Q.31 How are the following conversions
accomplished? (Write reaction only)
(i) Aniline to
Chloro-benzine
(ii) Nitrobenzene to phenol
(iii) Aniline to benzoic
acid (3 marks)
Q.32 Select the complex formation reaction
and write an expression for the stability constant of the complex species.
What information is conveyed regarding the strength of ligands from the
stability constant values of their complexes with a metal ion? Illustrate
your answer with example of monodentic ligands. (3 marks)
Q.33 (a) Explain giving reason each of he
following :
(i) CCl4 remains unaffected whereas
SiCl4 is easily hydrolysed by water.
(ii) Nitrogen exists as
a diatomic molecule, N2, whereas phosphorus exists as
tetra-atomic molecule, P4.
(iii) SF6 is known but
SH6 not known.
(b) Write the balance equation fro the
following reaction :
(i) B2H6 + LiH
--->
(ii) BrO3 + F2 + OH---->
(5 marks)
Q.34 (a)You are provided with 4 reagent :
LiAlH4, I2/NaOH, NaHSO3 and Sciff's
reagent. Write which two reagents can be used to distinguish between the
compounds in each of the following pairs :
(i) CH3CHO and
CH3COCH3
(ii) CH3CHO and
C6H5CHO
(iii)
C6H5COCH3 and
C6H5COCH3 and
C6H5COC6H5
(b) Account for
the following :
(i) The order of reactivity of halogen acids with ether
is HI > HBr > HCl
(ii) The pKa value of choloroacetic
acid is lower than the pKa value of acetic acid. (5
marks)
|
|
