Saturday 17 February 2018

2nd year Chemistry chapter 2 Important Short Questions

2nd year Chemistry chapter 2 Important Short Questions
Here we have written the 12th class chemistry chapter 2 S-Block Elements short questions which are important.

Chapter 02

Q1: Why the alkali metals show + I oxidation state?
Ans:: Since only one electron present in the valance shell of alkali metals hence they show
+ I oxidation state. Due to very high second ionization energies they cannot show +2
oxidation states.
Q2 : What are the most abundant elements among the alkali metals in earth’s crust?
Am: Na and K are most abundant elements of alkali metals found in earth crust they each
constitutes about 2.4% of the earth crust.
Q3 : Why the members of IA & lIA are calledihe alkali and alkaline earth metals?
Ans : The name alkali derived from Arabic term means ashes. Actually the metals of I -A
group like Na, K are present in the ash of plants. They produce strong alkaline solution in
water that why they are called the alkali metals.
The members of TI-A group are called alkaline earth metals because their
aqueous solution are strongly alkaline and also found in earth crust abundantly.
Q4 : Why CaCl2 added in NaCl in Down’s cell.
Ans : The melting point of NaCI 801°C degree and at at industrial scale such aft aining such
high temperature is economically not feasible therefore to reduce melting point of NaCI
about 20% CaCI2 is added to NaC1 so that it melts at 600°C degree.
Q5 : What is niilkof Lime andMilkof Magnesia?
Ans : A saturated solution of Ca(OH)2 is called milk of lime and is used as test for CO2 for
whit washing. Whereas the suspension of Mg(OH)2 in water is called milk of magnesia and
is used for treating the acidity.
Q6 Why alkali and alkalineearth metals are among the reactive elements of periodic table
Ans: Alkali metals and alkaline earth metals one two electrons in their valence shell Since
they possess larger atomic size and very low ionization energy in the periodic table and are
capable of losing the electrons easily to get the inert gas configuration therefore they are
among the most reactive elements of periodic table.
Q7: Name and give configuration of members of S-block element exhibiting the zero
oxidation state?
Ans: Helium is the member of s-block elements showing zero oxidation state with
electronic configuration is 2He = 1S 2
Q8: How lane and sand are used to take the glass?
Ans: When the lime is heated with sand at high temperature it gives is calcium silicate
which is used as the basis for glasses manufacturing.
Q9: Why lime is added to the acidic soil?
Ans Large quantities of lime are used in agriculture for neutralizing the acidic soils. It has
been observed in lime to acidic soil increase the amount of readily soluble phosphorus.
Q10: What is the function of calcium in plant growth?
Ans: Calcium is essential for the normal development of plants it stimulates the formation
of the proper root system. It is accumulated in the leaves and the bark stimulating the activity
of microorganism that produces the nitrates. It also affects the supply of available
phosphorus to plant. Soils containing are alkaline in nature.
Q11 Why 2% gypsum added in the cement? What is the role of gypsum in cement industry?
Ans: 2% Gypsum is added to the finely divided cement when the clinker ground finely. The
purpose of gypsum in the cement is to prolong the setting time of cement by preventing
cement from hardening too rapidly when the water is mixed with it.
Q12: Point out the two advantages of Down’s cell.
Ans: Following are advantages of Down’s cell:
*No metallic fog is formed
*Liquid sodium can easily be collected at 600 C degree
*MateriaƟ of cell are not corroded during the electrolysis
*Raw material used is cheap
Q13: Why alkali metals are not found free in nature?
Ans: Alkali metal is very reactive due to larger size and lower ionization energy having
strong tendency of reacting with other elements. So they are not found free in nature but in
the form of ions and minerals.
Q14: Why the aqueous solution of N4C03 is alkaline is nature
Ans: When Na2CO3 is dissolved in the water forming the aqueous solution it hydrolysis to
produce strong base NaOH and weak acid the H2C03 as shown by the reaction
Na2CO3+2H20 > 2NaOH + H2C03
Ql 5: Basic character of oxides increases down the group. Justify it.
Ans: The basic character of metallic oxide increases downs the group due to increase in
atomic size and lower ionization energy the metallic character increases (ability to lose the
electron) and thus the basic character of metallic oxide increased.
Ql 6: What are cement plaster and hard finish plater?
Ans: The plaster of Paris in which some adhesive material like glue or other oils have been
added to retard the setting and increase the setting time is called cement plaster.
The hard finish is made by calcination of anhydrous calcium sulfate with borax
or alum. This plaster set very slowly but gives the hard finish.
Q17: All the Carbonates earth metals are insoluble in water, but those of alkali metals are
soluble in water except for LCO3 Why?
Ans In case of alkali metals, due to larger ionic size of metal atom the lattice energy is
lower hence all the alkali metal carbonates are soluble in water except Li2CO3 which is due
to higher charge density but in case of alkaline metal carbonates due to smaller ionic size
the lattice energy increased and become insoluble in water.
Ql8: give the composition of solution that flows out of cathode compartment of Nelson’s
Ans: Solution following out of the cathode compartment contains 11% NaOH and 16%
NaC1 Evaporation of this solution crystallizes the less soluble NaCl which is filtered off.
liquid left contains about 50% NaOH having 1% NaCl as the impurity.

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