52671 + Interview Questions in Chemistry in Class 11

1.	Aluminium metal (atomic weight = 27 g) crystallises in the cubic system with edge length 4.0 Å. The density of metal is 27.16 amu/Å^(3). Determine the unit cell type and calculate the radius of the Aluminium metal.
Answer» ANSWER :FCC, `SQRT2 Å`

Discussion

2.	Aluminium is usually found in +3 oxidation state. In contrast, thallium exists in +1 and +3 oxidation states. This is due to....
Answer» Lattice EFFECT Lanthanoid contraction Diagonal RELATIONSHIP Inert pair effect Solution :`+1` is more STABLE form of Thallium DUE to inert pair effect. For Tl +1 `gt` +3 oxidation state.

Discussion

3.	Aluminium is used in the extraction of
Answer» CR Fe Ca MN Solution :ALUMINIUM is USED in the EXTRACTION of Cr and Mn.

Discussion

4.	Aluminium is stable in air and water inspite of the fact that it is reactive metal. The reason is that a thin film of its oxide, if formed on its surface which makes it passive for further attack. The layer is so useful that in industry, it is purposely deposited by an electrolytric process called anodizing. Reaction of aluminium with oxygen is highyl exothermic and is called thermite reaction2Al(s)+(3)/(2)O_(2)(g)rarr Al_(2)O_(3)(s), Delta H=-1670 kJThermite reaction finds applications in the metallurgical extraction of many metals from their oxides and for welding of metals. The drawback is that to start the reaction, high temperature is required for which an ignition mixture is used.Thermite mixture used for welding is
Answer» `Fe_(2)O_(3)` and Al powder BaO and MG powder FE and Al Cu and Al Solution :3 : 1 RATIO of `Fe_(2)O_(3)` and Al powder

Discussion

5.	Aluminium is stable in air and water inspite of the fact that it is reactive metal. The reason is that a thin film of its oxide, if formed on its surface which makes it passive for further attack. The layer is so useful that in industry, it is purposely deposited by an electrolytric process called anodizing. Reaction of aluminium with oxygen is highyl exothermic and is called thermite reaction2Al(s)+(3)/(2)O_(2)(g)rarr Al_(2)O_(3)(s), Delta H=-1670 kJThermite reaction finds applications in the metallurgical extraction of many metals from their oxides and for welding of metals. The drawback is that to start the reaction, high temperature is required for which an ignition mixture is used.Anodised aluminium is
Answer» Al obtained at ANODE Al PREPARED electrolytically Alloy of Al CONTAINING 95% Al Al electrolytically COATED with `Al_(2)O_(3)` Solution :Anodised aluminium is Al electrolytically coated with `Al_(2)O_(3)`

Discussion

6.	Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. In electrolysis of Al_(2)O_(3) by Hall and Heroult process
Answer» Cryolite `(Na_(3)AlF_(6)` lowers the melting point of alumina `(Al_(2)O_(3))` and INCREASES its eletrical conductivity. Al is OBTAINED at cathode and `CO_(2)` at anode. Both A and B are correct None of A, B are correct. Solution :N//A

Discussion

7.	Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. Which one of the following benefication processes is used for the mineral Al_(2)O_(3)2H_(2)O
Answer» FROTH floatation Leaching Liquation Magnetic separation Solution :N//A

Discussion

8.	Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. Which of the following metals are extracted by electrolytic reaction
Answer» Copper Aluminium Zinc Silver Solution :N//A

Discussion

9.	Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. Which mineral has been named correctly
Answer» Bauxite `(Al_(2)O_(3)2H_(2)O` Corrundum `Al_(2)O_(3)` CRYOLITE `Na_(3)AlF_(6)` Feldspar `Be_(3)Al_(2)Si_(6)O_(13)` SOLUTION :N//A

Discussion

10.	Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. Principle ore of aluminium is
Answer» Bauxite Corrundum Cryolite Feldspar. Solution :N//A

Discussion

11.	Aluminium is obtained by
Answer» reducing `Al_(2)O_(3)`with coke electrolysing `Al_(2)O_3` , DISSOLVED in `Na_(3) AlF_6 ` reducing `Al_(2)O_3`with chromium heating `Al_(2)O_3`and cryolite Answer :B

Discussion

12.	Aluminium is most abundant in earth's crust, yet it is obtained from bauxite because
Answer» Bauxite is AVAILABLE in large quantity of easy extraction of AL from it Bauxite contains maximum Al Bauxite is less impure Solution :Aluminium is most ABUNDANT in earth's CRUST YET it is obtained from bauxite because it is available in large quantity.

Discussion

13.	Aluminium is more reactive thant iron. But aluminium is less easily coroded than iron because:
Answer» ox ygen forms a PROTECTIVE OXIDE layer on aluminium aluminium is a noble metal iron undergoes reactions easily with water iron forms MONO and divalent IONS. ANSWER :A

Discussion

14.	Aluminiumis "………….." in nature and dissolves in both dilute hydrochloric acid and sodium hydroxideevolving "………….." gas.
Answer» ANSWER :AMPHOTERIC, `H_(2)`

Discussion

15.	Aluminium is extracted from Alumina (Al_(2)O_3 ) by electrolysis of a molten mixture of
Answer» `Al_(2)O_3` + HF + `NaAlF_4` `Al_(2)O_3 + CaF_2 + NaAlF_4` `Al_(2)O_3` + `Na_(3)AlF_6` + `CaF_2` `Al_(2)O_3` + KF + `Na_(2)Al_(6)` Solution :N//A

Discussion

16.	Aluminium is extracted by the electrolysis of
Answer» Bauxite ALUMINA Alumina MIXED with molten cryolite Molten cryolite Solution :ALUMINIUM is extracted by the ELECTROLYSIS of alumina (PURE `Al_(2)O_(3)`) mixed with moleten cryolite.

Discussion

17.	Aluminium (III) chloride forms a dimer because
Answer» Higher co-ordination can be ACHIEVED by Al Al has HIGH ionisation energy Al belongs to THIRD group It can not form a trimer Solution :Aluminium (III) CHLORIDE forms a dimer because higher co-ordination can be achieved by Al.

Discussion

18.	Aluminium (III) chloride forms a dimer because aluminium
Answer» cannot FORM a trimer has HIGH IONISATION energy belongs to third group can have higher coordination NUMBER. Solution :can have higher coordination number.

Discussion

19.	Aluminium forms AlF_(6)^(3-)but borondoes not form BF_(6)^(3-).Why so ?
Answer» Solution :Al, on the OTHERHAND,DUE to the persence ofd-orbitals canexlendits valency UPTO a maximum of 6 andforms `AlF_(6)^(3-)`.

Discussion

20.	Aluminium fluorirde is ionic but aluminium chloride is covalent. Explain
Answer» Solution :FIRSTLY, the electronegitivity differencebetween `Al(1.5)` and `Cl(3.0)` is `1.5` whilethat between `Al(1.5)` and `F(4.0)` is `2.5`. As a result, aluminium-fluorine is ionic while that between aluminium-chloride is covalent. Secondly, `Al^(3+)` (53.5 pm) is very small as COMPOUND to `F^(-)` (136 pm) and `Cl^(-)`(181 pm) . Since ACCORDING to Fajan rule, the ssame cation can polarize a biggeranion(i.e., `Cl^(-)`)more easily than a SMALLER anion (i.e,`F^(-)`)therefore, `Cl^(-)`can donate electrons back to `Al^(3+)` more easily than `F^(-)`. In other words, `AlCl_(3)` is covalentwhile `AlF_(3)` isionic.

Discussion

21.	Aluminium exhibits diagonal relationship with
Answer» Beryllium Silicon Carbon Germanium Answer :A

Discussion

22.	Aluminium dissolves in mineral acids and aqueous alkalis and thus shows amphoteric character. A piece ofaluminium foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning match stick near the mouth of the test tube, a pop sound indicates the evolutionof hydrogen gas. The same activity when performed with concentrated nitric acid, reaction doesn't proceed . Explain the reason.
Answer» Solution :Aluminum is amphoteric in nature ,it reacts with acid and base to give salt and `H_2` gas. It burns with POP SOUND . `2Al+6HCl to 2AlCl_3 + 3H_2` `2Al+NaOH + 2H_2O to 2NaAlO_2 + 3H_2` When Al reacts with conc. `HNO_3` , a THIN layer of `Al_2O_3` on the surface of Al metal which protect further reaction. This layer is CALLED protective layer. `2Al+6HNO_3 to Al_2O_3 + 6NO_2 + 3H_2O`

Discussion

23.	Aluminium dissovles in mineral acids and aqueous alkalies and thus shows amphoteric character. A place of aluminum foil is treated with dilute hydrochloric acid or dilute sodium hydroxide solution in a test tube and on bringing a burning match stick near the mouth of the test tube, a pop sound indicates the evolution of hydrogen gas. The same activity when performed with concentrated with concentrated nitric acid. reaction doesn't proceed. Expalin the reason.
Answer» Solution :Aluminium being amphoteric in nature dissolves both in acids and alkalies evolving `H_(2)` gas which burns with a POP sound `2Al+6HClrarr2AlCl_(3)+3H_(2)` `2Al+NaOH+2H_(2)Orarrunderset("Sodium meta aluminate")(2NaAlO_(2))+3H_(2)` But when Al is TREATED with conc. `HNO_(3)`, a thin protective layer of `Al_(2)O_(3)` is formed on its SURFACE which prevents further action `2Al + 6HNO_(3) RARR Al_(2)O_(3)+6NO_(2)+3H_(2)O`.

Discussion

24.	Aluminium crystallises in a cubic close packed structure. Is metallic radius is 125 pm. (i) What is the length of the side of the unit cell ? (ii) How many unit cells are there in 1-00 cm^3 of aluminium ?
Answer» SOLUTION :(i)ccp=fcc. For fcc, `a=2sqrt2r`= 2 X 4.414 x 125 pm =354pm (ii)Volume of one unit cell =`(354xx10^(-10)cm)^3=4.44xx10^(-23) cm^3` Unit CELLS in `1 cm^3 =1/(4.44xx10^(-23))=2.25xx10^22`

Discussion

25.	Alumiunium chloride exists as dimer, Al_(2)Cl_(6) in solid state as well as in solution of non - polar solvents such as C_(6)H_(6). When dissolved in water it gives :
Answer» `Al_(2)O_3+6HCl` `[Al(H_(2)O)_(6)]+3C^(-)` `[Al(OH)_(6)]^(3-)+3HCL` `Al^(3+) +3Cl^(-)` Solution :`AlCl_(3)+6H_(2)O rarr [Al(OH)_2]^(+3)+3HCl+3H^(+)`

Discussion

26.	Aluminium chloride exists as a dime. Give reasons .
Answer» Solution :In `AlCl_(3)`, Al hasonly six electrons in the valence shell. Therefore it needs two moreelectrons to completeits octet.To do so, it accepta lone pairof electronsfrom theCl ATOM of another `AlCl_(3)` moleculeas shown. As a RESULT , `AlCl_(3)` exiss as a DIMER.

Discussion

27.	Aluminium cation is acidic. Why?
Answer» Solution :Aluminium CATION, `AL^(3+)` has empty orbitals available to accept electrons. Hence, `Al^(3+)` ion is a Lewis acid. `Al^(3+)` cation forms COMPLEX IONS like `[AlF_(6)]^(3-) ,[Al(OH)_4(H_2 O)_2 ]^(-)`, etc.` [Al^(3+)+6F^(-) to(AIF_(6))]^(3+)`

Discussion

28.	Aluminium becomes passive in
Answer» conc `HNO_3` `H_(2)Cro_(4)` `HCIO_(4)` conc.HCI Solution : DUE to formation of OXIDE LAYER on the sur face 3. X is NH,

Discussion

29.	Aluminium alloy with beautiful golden yellow colour used for making artificial jewellery is
Answer» Duraalumin Magnalium Alclad ALUMINIUM BRONZE Solution :Aluminium bronze has a BEAUTIFUL GOLDEN yellow colour.

Discussion

30.	Aluminimumdissolvesin mineralacids and aqueousalkalies and thus showsamphotericcharacter place ofaluminiumfoil istreatedwith dilutehydrochloricacid or dilutesodium hydroxide solutiona test tube andon bringing a burning matchstick near the monthof thetest tube , a pop southindicatesthe evolutionof hydrogengas. Thesame activitywhenperformedwith concentratednitrogen acid, reaction doesn'tproceed. Explain the reason.
Answer» Solution :Al being amphoteric dissolvesboth in acidsand alkalies evolving`H_(2)` gas whichburnswith a popsouth `2Al + 6HCl rarr AlCl_(3) + 3H_(2)` `2Al + 2NaOH + 2H_(2)O rarr underset(" Sod. Meta-aluminate ")(2 NaAlO_(2)) +3H_(2)` With CONC. `HNO_(3)`, Al becomespassive and the reactiondoes not proceed.This passiveis DUE to fromationof a thinpratectivelayer of its oxide `(Al_(2)O_(3))` on the surfaceof themetalwhich preventsfurther ACTION. `2Al + 6HNO_(3) rarr Al_(2)O_(3) + 6NO_(2) + 3H_(2)O`.

Discussion

31.	Alumina is
Answer» acidic Basic AMPHOTERIC none of these Solution :Alumina `(Al_(2)O_(3))` is amphoteric is NATURE. It dissolves both in ACIDS and alkalies.

Discussion

32.	Alum is used in dyeing industry as
Answer» For fire PROOFING fabircs As FIRST -aid for cuts For SOFTENING hard water As mordant Answer :4

Discussion

33.	Alum is used by dyers of clothes
Answer» for fire proofing fabrics as first-aid for cuts for softening HARD water as mordant Solution :The `Al^(3+)` ions PRODUCED, when potash alum is dissolved in water, ACT as a mordant in the process of DYEING of CLOTHES.

Discussion

34.	Alum is found to contain hydrated monovalent cation [M(H_(2)O)_(6)]^(+),trivalent cation [M'(H_(2)O)_(6)]^(3+)and SO_(4)^(2-) in the ratio of
Answer» `1:1:1` `1:2:3` `1:3:2` `1:12` ANSWER :4

Discussion

35.	Alum is a water purifier because it
Answer» softness HARD water COAGULATES the impurities destroys the PATHOGENIC bacteria gives taste Solution :ALUM coagulates the suspended or colloidal impurities.

Discussion

36.	Alum helps in purifying water by
Answer» FORMING Si complex with clay particles sulphate part which combines with DIRT and removes it aluminium which COAGULATES the MUD particles making mud water soluble. Solution :Alum help in purifying water by `Al^(3+)` ions which coagulate the negative mud particles.

Discussion

37.	Alum helps in purification water by
Answer» forming Si complex with clay particles sulphate part which COMBINES with dirt and removes it. aluminium which COAGULATES the MUD particles making mud water soluble Solution :Alum helps in purifying water by coagulating the negatively charged mud particles with `Al^(3+)` ions provided by it

Discussion

38.	Although the dissolution of ammonium chloride in water is an endothermic reaction, even then it is spontaneous because
Answer» `DELTA H` is POSITIVE , `Delta S` is -ve `Delta H` is + ve, `Delta S` is zero `Delta H` is positive, `T Delta S lt Delta H` `Delta H` is +ve, `Delta S` is positive and `Delta H lt T Delta S` Solution :EVEN if `Delta H gt 0`, if `Delta S gt 0 and Delta H - T Delta S lt 0` then spontaneous.

Discussion

39.	Although thallium (Z = 81) has only slightly higher atomic radius (170 pm)than that ofindium (167 pm)butits ionizationenthalpy (589 kJ "mol"^(-1))is much higherthan that ofindium (558 kJ "mol"^(-1)) . Explainwhy /
Answer» Solution :Althrough on movingfrom `In (Z = 49)` to `TL (Z = 81)`, the nuclearincreases by 32units `(81-49)`yet due to poor SHIELDING effect on intervening 4f- and5d-electrons,effectivenuclear chargeaction on Tl is much higherthan that on Inand hence `Delta_(i)H_(1)`of `Tl`is much higherthan that of `In`.

Discussion

40.	Although ozone is heavier than air, it does not settle down near the earth why ?
Answer» SOLUTION :Ozone is thermodynamically unstable and DECOMPOSES bask to molecular oxygen before REACHING NEAR earth's surface. (ii) As negligible amount of UV - rays reach near the surface the formation of ozone near the surface of earth is RARE.

Discussion

41.	Although nitrogen and chlorine have very nearly same electronegativity yet nitrogen forms hydrogen bonding while chlorine does not. Why?
Answer» Solution :Due to bigger size of Cl as compared to N, electron DENSITY PER unit volume on N is higher than on Cl. As a result N can attract the H aotms of `H_(2)O` more strongly than Cl. THUS, N forms H-bonds but Cl does not.

Discussion

42.	Although nitrogen does not absorb on the surface at the room temperature, it absorbs on the same surface at 83 K. Which one of the following statement is correct ?
Answer» At 83 K, there is formation of monomolecular layer At 83 K, there is formation of multi molecular layer At 83 K, nitrogen molecules are held by chemical bonds. At 83 K, nitrogen is ABSORBED as atoms. Solution :At 83K there is physisorption and hence multimolecular layer FORMED..

Discussion

43.	Although heat is a path function but heat absorbed by the system under certain specific conditions is independent of path. What are those conditions ? Explain.
Answer» Solution :The two conditions under which heat BECOMES independent of path are (i) when volume remains constant (ii) when pressure remains constant Explanation (i) At contant volume. By first LAW of thermodynamics, `DELTA U = Q + W " or " q = Delta U - W`. But `W = - p Delta V` HENCE, `q = Delta U + p Delta V`. But as volume remains constant `Delta V = 0` `:. q_(v) = Delta V " but " Delta U` is a state function. Hence, `q_(v)` is a state function. (ii) At constant pressure. As we know, `q_(p) = Delta U + p Delta V`. But `Delta U + p Delta V = Delta H`. `:. q_(P0 = Delta H`, as `Delta H` is a state function therefore, `q_(p)` is a state function.

Discussion

44.	Although geometries of NH_3 and H_2O molecules are distorted tetrahedral,bond angle in water is less than that of ammonia.Discuss.
Answer» Solution :In `NH_3`,there is only one pair on nitrogen atom to repel the BOND pairs WHEREAS in `H_2O`, there are two lone pairs on OXYGEN atom to repel the bond pairs.Hence the repulsion on bond pairs is greater in `H_2O`, than in `NH_3` and so the bond ANGLE is LESS.

Discussion

45.	Although geometries of NH_(3) and H_(2)O molecules are distorted terahedral bond angle in water is less than that of ammonia. Discuss.
Answer» Solution :In `NH_(3)` on N only one lone pair and THREE N - H bonding pair are present so it is `AB_(3)`E type molecule. In `H_(2)`O one lone pair so due to repulsion it has trigonal pyramidal SHAPE and H - N - H bond angle is `107^(@)` while in `H^(2)`O due to repulsion of two lone pair `H_(2)`O has BENT shape and bond angle is `10.5^(@)`.

Discussion

46.	Although geometries of NH_(3) and H_(2)O moleculesare distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.
Answer» Solution :`NH rarr NH_(3)` `H_(2)O rarr H_(2)O:` Because of two lone pair of electrons on O-atom, repulsion on bond PAIRS is greater in `H_(2)O` in COMPARISON to `NH_(3)`. THUS, the bond angle is less in `H_(2)O` molecules.

Discussion

47.	Although geometries of NH_(3) and H_(2) Omolecules are distorted tetrahedral, bond angle in water is less thenthat of ammonia.Discuss .
Answer» Solution :In ` NH_(3)`, there is only one lone pair on N-atom to REPEL the bond pairs whereas in ` H_(2)O` , there are TWO lone pairs on O-atom to repel the bond paris . Hence the repulsions on bond pairs are GREATER in ` H_(2) O `than in ` NH_(3)` andhence the bond angle is LESS.

Discussion

48.	Although for Mg, Delta_iH(378 kJ mol^(-1)) is greater than Delta_iH_2 (1450 kJ mol^(-1)), Mg prefers to form MgCl_2 rather than MgCl because
Answer» `MG^(2+)` ion has the noble gas configuration `Mg^(2+)` ion is smaller than `Mg^(+)` `Mg^(2+)` ion has HIGHER CHARGE than `Mg^(+)` ion the lattice enthalpy of `MgCl_2` is very high Solution :Lattice enthalpy of `MgCl_2(2527 kJ mol^(-1))` is more than ENOUGH to COMPENSATE for the energy needed to remove the first two electrons from an `Mg` atom (`738 kJ mol^(-1)+1450 kJ mol^(-1)=2188 kJ mol^(-1)`).

Discussion

49.	Although fluorine ismuch more electronegative then hydrogen yet the dipole moment of NF_(3) (0-24 D) is much lower than that of NH_(3) (1-46 D). Explain.
Answer» Solution :The dipole moment of MOLECULES having lone PAIRS andpolar bonds is the vector sum of the following two moments. (i) Dipole moment of the lone pair/s (ii) Resultant of the dipole moments of polar bonds. Now both `NH_(3)andNF_(3)` have pyramidal sturctures with FNF and HNH bond ANGLES of `102.4^(@)and107.8^(@)` respectively. The direction of the dipole moment of the lone pair is in the same direction, i.e., away from the N atom as indicated in the Fig. 11.37 Since N is more electronegative than H, therefore, the direction of the N-H bond moments is from H to N. The resultant of these three bonds adds to the moment of lone pair hence the net dipole moment of `NH_(3)` is1.46 D. In contrast, F is more electronegative than N and hence the direction of the N-F bond moments is from N to F. The reusltant of these three dipole moments opposes the dipole moment of the lone pair and thus partly CANCELS the resultant of the dipole moments of the three N-H bonds in`NH_(3)`. In other words, the only difference if that in case of `NF_(3)`, the dipole moments of the lone pair. Consequently, `NF_(3)` has a much LOWER dipole moment (0.24 D) than that of `NH_(3)` (1.46 D).

Discussion

50.	Although every element is different from every other element, yet some elements have certain similarities. Based upon these similarities, the scientists after numerous attempts were are given. Based upon these multiple choice questions are ultimately sucessful in arranging the various elements into groups or chemical families in such a way that similar elements were put together. This arrangement of elements is calledclassification of elements and this led to the formulation of a periodic table. The periodic table is the most organising principle in chemistry. If you know the properties of any element in a group, or of the columns, of the periodic table, you can make a good guess atthe properties of every other element in the same group and even the elements in the neighbouring groups. The first break through in the classification of elements, was provided by Russian chemist Dmitri lunovich Mendeleev. Taking thechemistry of the elements as his primary organising principle, he arranged the known elements by atomic mass and grouped them together according to their chemical reactivity He also observed that there occurred recurrence of elements with similar physical and chemical properties after certain regular intervals. On the basis of these similarities Mendeleev proposed his periodic law which states that physical and chemical properties of lementsare a periodic function of their atomic masses Moseley suggested that atomic number was a better fundamental property of an element than its atomic mass. This forms the basis of the Modern periodic law. Thus, modern periodiclaw states that physical and chemical properties of the elements are a periodic function of their atomic numbers.In the modern long form of periodic table the elements are arranged in the increasing orderof their atomic numbers and the elements with similar properties repeat after regular intervals. Repetition of chemical properties of elementsat regular intervals when arranged in a definiteorder is called periodicity of properties. This is due the recurrence of similar outer electronic configuration at certain regular intervals. The long form of periodic table may be divided into four main blocks known as s, p, d and f blocks depending upon the type of orbitals being filledup with the increase in atomic number in atoms of the elements. The nature of the block to which an element belongs depends upon the type of subshell which receives the last electron. The electronic configuration of the element which is just above the element with atomic number 43 in the same periodic group
Answer» `1s^(2)2S^(2)2p^(6)3S^(2)3p^(6)3d^(5)4s^(2)` `1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(2)5P^(5)` `1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(1)` `1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10)4s^(1)4p^(6)` Answer :A

Discussion

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