2nd Year Chemistry Notes Chap 2

                                                                  Important Questions

Q1 : Why the alkali metals show +1 oxidation state ?

Ans : Since only one electron present in the valance shell of alkali metals hence they show +1 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 ?

Ans : Na and K are most abundant elements of alkali metals found in earth crust they each consitutes about 2.4% of the earth crust.

Q3 : Why the members of IA & IIA are called the alkali and alkaline earth metals ?

Ans : The name alkali drived from Arabic term means ashes. Actually the metals of 1-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 numbers of  II-A group are called akaline earth metals beacause 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 NaCl 801 C degree and at at industrial scale such attaining such high temrature is economically not feasible therefore to reduce melting point of NaCl about 20% CaCl2 is added to NaCl so that it melts at 600 C degree.

Q5 : What is milk of Lime and Milk of Mafnesia ?

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 alkaline earth metals are among the reactive elements of periodic table ?

Ans: Alkali metals and alkaline earth metals one two electron in their valance shell. Since they possess larger atomic size and very low ionization enegy in 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 = 1S2

Q8: How lime and sand are used to amke the glass ?

Ans: When the lime is heated with sand at high temprature it gives is calium selicate which is used as basis for glasses manufacture.

Q9: Why lime is added to the acidic soil ?

Ans: Large quantities of lime are used in agriculture for neutarlizing the acidic soils. It has been abserved of lime to acidic soil increase the amount of readily slouble phosphorus 

Q10: What is the function of calcium in plant growth ?

Ans: Calcium is essential for the normal development of plants it stimulate the formation of prooper root system. It is accumulated in the leaves and the bark stimulating the acitivity 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 role of gypsum in cement indutsy ?

Ans: 2% Gypsum is added to the finely divided cement when tke clinker ground finely. The porpuse of gypsum in the cement is to prolong the setting time of cement by preventing cement from hardning 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
                 *Liqued sodium can easily be collected at 600 C degree
                  *Materials of cell are not corroded during the electrolysis
                  *Raw matrial used are cheap

Q13: Why alkali metals are not  found free in nature ?

Ans: Akali metal are 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 Na2CO3 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 H2CO3 as shown by the reaction

Na2CO3+2H2O---------> 2NaOH + H2CO3

Q15: Basic character of oxides increases down the group. Justify it.

Ans: The basic character of matallic oxide increases down 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.

Q16: What is 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 calination of anhydrous calium sulphate with borax or alum. This plaster set very slowly but gives hard finish.

Q17: All the Carbonates earth metals are insoluble in water, but those of alkali metals are soluble in water except Li2CO3 Why?

Ans:  In case f 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 the become insoluble in water.

Q18: give the composition of solution that flows out of cathode compartment of Nelson's Cell ?

Ans:  Solution following out of the cathode compartment contains 11% NaOH and 16% NaCl. Evaporation of this solution crystallize the less soluble NaCl which is filtered off liquid left contains about 50% NaOH having 1% NaCl as impurity.

                                               By Rana Rehman
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