Braj Education Centre
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1.
Class
:
XII
Subject
:
Chemistry
Assignment Topic
:
P-Block Elements (Gr 15 and 16)
What are the two most important oxidation states of Group 16 elements of the periodic
table?
2.
Explain: SiCl4 forms [SiCl6] 2- while CCl4 does not from [CCl6] 2-
3.
a) In the ring test for identification of nitrate ion, what is the formula of the compound
responsible for the brown ring formed at the interface of two liquids?
b) What is the covalence of nitrogen in N2O5?
4.
Mention any two of the four characteristics of sulphuric acid responsible for its chemical
reactions. Show chemical reactions to illustrate it
5.
When conc. H2SO4 was added into an unknown salt present in a test tube, a brown gas
(A) was evolved. This gas intensified when copper turnings were also added into this
test-tube. On cooling, the gas (A) changed into a colourless gas (B).
6.
a)
Identify the gases A and B.
b)
Write the equations for the reactions involved.
Draw the structures of white phosphorus and red phosphorus. Which one of these two
types of phosphorus is more reactive and why?
7.
Explain the following order of boiling point of group 15 hydrides: PH3 < AsH3< NH3 <
SbH3 < BiH3
8.
Concentrated sulphuric acid is added followed by heating to each of the following test
tubes labelled 1 to 5 Identify in which of the above
test tube the following change will be observed.
Test
Chemical Present
Support your answer with the help of a chemical
Tube
equation.
Number
a)
Formation of black substance
1
Cane Sugar
b)
Evolution of brown gas
2
Sodium Bromide
c)
Evolution of colour less gas
3
Copper Turnings
d)
Formation of brown substance which on dilution
4
Sulphur Powder
becomes blue.
5
Potassium
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e)
Disappearance of yellow powder along with evolution of colourless gas.
Arrange the following in increasing order of property indicated for each set (Give a brief
9.
explanation for your answer) i) HF, HCl, HBr, HI Increasing acid strength
10.
Which of the following two bonds is stronger? Why? N − N or P − P
11.
Why is NO paramagnetic in gaseous state, but diamagnetic in liquid and solid states?
12.
Why do oxides of nitrogen have open structure, but those of phosphorus have cage
structure. Illustrate your answer with the help of a suitable example.
13.
Why is Bismuth a strong oxidizing agent in the pentavalent state?
14.
Why is H 2 S acidic but H 2O neutral: P4 + SO2Cl2
15.
Account for the following:
I.
The stability of + 5 oxidation state decreases down the group in group 15 of the
periodic table
II.
III.
Solid phosphorus pentachloride behaves as an ionic compound.
All the bonds in PCl5 are not equivalent. Also support this observation with the
help of a chemical reaction
IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
Bond angle of PH3 is less than that of NH3
Of Bi (V ) and Sb (V ) which may be the stronger oxidising agent and why?
Sulphur in vapour state exhibits Para magnetism
Fluorine is the strongest oxidant amongst the halogens
SF6 is not easily hydrolyzed whereas SF4 is readily hydrolyzed. Explain!
PCl5 is known, but NCl5 is not.
H 3 PO3 is diprotic or dibasic
In
group
15,
the
H − M − H bond
angles
decreases
in
the
following
order NH 3 (107.50 ) > PH 3 (93.60 ) > AsH 3 (91.80 )
XII.
XIII.
XIV.
XV.
XVI.
Nitrogen is inert, but P reactive.
Nitric oxide becomes brown when released in air.
Solid phosphorus pentachloride exhibits ionic character
O2 is gas, but S8 is solid at room temperature
H 2 S acts only as a reducing agent, but SO2 acts both as a reducing and an oxidizing
agent.
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XVII.
H3PO2 and H3PO3 act as good reducing agents while H3PO4 does not.
XVIII.
On addition of ozone gas to KI solution, violet vapours are obtained.
XIX.
XX.
XXI.
XXII.
XXIII.
CN¯ ion is known but CP¯ ion is not known.
NO2 dimerises to form N2O4
PbO2 is a stronger oxidising agent than SnO2.
H3PO2 acts as a monobasic acid. .
The basic character among the hydrides of Group 15 elements decreases with
increasing atomic numbers.
XXIV.
XXV.
XXVI.
XXVII.
Sulphur vapour is paramagnetic
Ammonia has greater affinity for protons than phosphine
Sulphur has a greater tendency for catenation than oxygen
In the structure of HNO3, The N – O bond (121pm) is shorter than N – OH bond
(140pm)
XXVIII.
XXIX.
XXX.
All P – Cl bonds in PCl5 are not equivalent
+3 oxidation state becomes more stable from As to Bi
In solutions of H 2 SO4 in water, the second dissociation constant K a2 is less than the
first dissociation constant K a1
XXXI.
16.
Concentrated nitric acid turns yellow when exposed to air
Describe the favourable conditions for the manufacture of
a)
Ammonia by Haber’s Process
b)
Sulphuric acid by contact Process
17.
Draw the structures of a) PCl5 b) S8
18.
What happens when orthophosphoric acid is heated?
19.
Complete the following equations
A) Ca3 P2 ( s ) + H 2O (l ) →
B) Cu 2+ ( aq) + NH 3 ( aq )( excess ) →
C) PH 3 + HgCl2 →
20.
Which one has higher electron gain enthalpy with negative sign: sulphur or oxygen and
why?
21.
Sulphur disappears when boiled with aq. Solution of sodium sulphite?
Ans: Due to the formation of soluble sodium thiosulphate
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22.
Which oxide of sulphur acts as an oxidising as well reducing agent? Why?
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