|B.Sc(H) Chem/II -NS
Paper - VII
(Group-I & II)
Assignment given by Dr.Manisha Jain
Assignment Distribution Date 20.09.2009………
Last date for submission of Answer sheet 26.09.2009…
Q.1. Justify the following statements:
a.Alkali metals are not extracted by usual procedures of reduction of their oxides or their displacement in aqueous solutions by more electropositive elements.
b.When alkali metals are reacted with air, Li mainly forms monoxide, Na predominantly forms peroxide whereas others form superoxides also besides peroxide and mono-oxide.
c.Thermal stability of alkali metal carbonates increases down the group.
d.Lithium is the only alkali metal in group I to form a nitride by direct reaction with nitrogen.
e.Expected dipole moment of LiI (if fully ionic and in gaseous state) should be 11.5 D, but its experimental value is 3.25 D.
f.The solubility of Group II sulphates decreases down the group.
g.Linear molecules X-Be-X exist only in the gas phase.
h.Aqueous solutions of alkaline earth metal sulphides smell of H2S on keeping.
i.Alkali metals and coinage metals, both belong to Group I ( IA and IB) respectively. But their resemblances are slight while differences are more prominent.
j.Alkaline earth metal bicarbonates donot exist in solid state.
10 x 2.5 marks
Q.2. Discuss the factors, which affect the stability of crown ether complex with an alkali metal cation.
Q.3. When alkali metals dissolve in liq. NH3, a blue coloured solution is obtained whose intensity increases with increase in concentration of alkali metal. After a certain metal to solvent ratio, the addition of more metal causes phase separation, a bronze coloured phase floating over the top of the deep blue coloured layer. Explain (i) why the colour of the solution is blue, (ii) Why is the bronze coloured liquid lighter than blue coloured solution. Compare the magnetic properties and electrical conductance of blue and bronze phases.
Q.4. When a white substance A was treated with dil. HCl, a colourless gas (B) was evolved, which turned moist litmus paper red. On bubbling (B) through lime water a precipitate (C) was formed, but further passage of gas (B) resulted in a clear solution (D). A small sample of (A) was moistened with conc. HCl and introduced in flame produsing a green colouration. On strong heating (A) decomposed giving a white solid (E), which turned red litmus paper blue. 1.9735 g of (A) was heated strongly and 1.5334 g of (E) was obtained as a product. The sample of (E) was dissolved in water and volume made upto 250 ml in standard flask. 25 ml of aliquots were treated with acid and required 20.30 ml of 0.0985 M HCl. Name the compounds (A) to (E) and give equations of chemical reactions. Calculate the gram molecular weight of (A).
Q.5. A soft silvery white metal (A) burns with a golden yellow flame to give a yellow powder B which on treatment with water liberate oxygen giving a clear solution c. The solution C placed on Al attacks this metal, liberating a gas D and forming a water-soluble compound E. The metal (A) dissolves in liquid NH3 to form deep solution, which is a good conductor and an excellent reducing agent. Identify A, B, C, D and E, and explain the observations.
Q.6. Complete the following equations:
1. BeCl2 + N2O4 ethyl acetate ? 120°C ?
2. NaNO3 800°C
3. BaO2 + HCl
4. KOH + NO
5. Na2O2 + CO2
6. KO2 + CO2