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Inorganic Chemistry
11 Aug 2007 14:19:46 IST
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dear all goiitians....
we know...p block is such a vast topic...with so many reasoning questions....
so here is a topic started to tackle all such reasoning questions.....with answers
hope it proves to be useful.........!!
this is a topic not posted in community shelf just to involve the participation of more and more goiitians........and continue the flow of the topic....
so lets begin.....
Comments (18)
11 Aug 2007 15:01:34 IST
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hi
1)CO2 is a gas but SiO2 is a solid.why?
ans:C does not have vacant d-orbitals and thus cannot form d pie-p pie bond to form a 3D structure.
2)C shows extensive catenation but others of the same group do not.why?
ans:C is small in size and the C-Cbond strength is high.but as we go down the group,electro negativity decreases as size increases.thus bond strength decreases and so does the catenation property.
!!!!!!!!!!!!!!!!!!!!
11 Aug 2007 15:10:28 IST
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Q. why does ammonia act as a complexing agent.
A: N: has a lp. can act as ligand.
Q: why nitrogen exist as N2 but phosphorous a P4
A: nitrogen can form only P pi - P pi bonds. due to absence of d orbitals.
Phosporous due to vacant 3d orbital can form d pi- p pi bonds.
thereby extend co ordination number.
Q: Why boiling point decreases decreases down a group?
A: hydrogen bonding decreases down a group.
hydrogen bonding can also be used to explain why H2O is liqiud. H2S is gas.
11 Aug 2007 23:56:39 IST
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grp 13 ....continued
* m.p and b.p of B > Al .why ?
due to small size and efficient packing of boron in crystal lattice
* order of reducing power : Al > Ga > In > Tl . why ?
becoz down the grp , electrode potential increases and reducing power decreases .
* why boric acid (H3BO3) is a monobasic acid even when it contains 3 hydroxl groups ??
boron atom is small in size and has only 6 electrons in its valence shell in boric acid . so it accepts a l.p. of electrons from the oxygen atom of H2O to form a hydrated species .
so the positively charged oxygen atom pulls sigma electrons of O-H bomd towards itself , releasing a proton .
so the positively charged oxygen atom pulls sigma electrons of O-H bomd towards itself , releasing a proton .
* conc HNO3 can be stored in aluminium containers . why ??
becoz Al on reacting with the acid forms a protective layer of Al2O3 which prevents further reaction between metal and acid .
*AlF3 is more ionic than AlCl3 .why ?
Fluoride ion is smaller than chloride ion and is less polarised by Al3+ to show ionic character .
it is becoz of the same reason that AlF3 has greater m.p than AlCl3
it is becoz of the same reason that AlF3 has greater m.p than AlCl3
* why all bonds Al -Cl bonds in Al2Cl6 are not equivalent ?
in Al2Cl6 each Al atom forms 3 covalent bonds with three chlorine atoms and one co -ordinate bond with the chlorine atom of another AlCl3 molecule.
in Al2Cl6 each Al atom forms 3 covalent bonds with three chlorine atoms and one co -ordinate bond with the chlorine atom of another AlCl3 molecule.
* why alumina cannot be reduced by carbon ?
at high temp. alumina reacts with carbon to form aluminium carbide.....
2 Al2O3 + 6C ---Ã Al4C3 + 3CO2
* Sodium carbonate (washing soda should not be kept in Al containers . why ?
Sodium carbonate reacts with water to form sodium hyroxide which in turn will react with the container and hydrogen gas will be evolved .
Na2CO3 +2H2O --Ã 2NaOH + H2CO3
Al + 2NaOH + 6H2O -----Ã 2Na[ Al (OH ) 4 ] + 3H2
* why anhydrous AlCl3 cannot be prepared by heating AlCl3.6H2O ?
bcoz hydrated aluminium chloride on heating undergoe hydrolysis to produce Al2O3.
12 Aug 2007 04:36:22 IST
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ummm...lemme contribute some...
Q)Why is diamond a bad conductor of electricity but a good conductor of heat?
ANS) conduction of electricity requires movement of electrons whereas conduction of heat doesnt req. movt. of electrons//
Q) Explain y silicon shows a higher covalency than carbon?
ANS) Si because of presence of d-orbitals (vacnat) can show a covalency upto 6 while C doesnt have ne d-orbitals so it has max. covalency of 4
Q) BH4^- & NH4^+ are isolobal...explain??
ans) both have tetrahederal shapes (sp3 hyb.) so both have 4 lobes...so they are isolobal
Q)Wich compound led the discovery of noble gases??
ans) PtF6 reacts with O2 forming O2+ [PtF6] -
Q) y grp 16 elements are called chalcogens?
ans) because many metals are found as oxides and sulphides and few as selenides and tellurides ......CHALCOGENS MEANS ORE FORMING
Q)What is laughing gas , how is it prepared?
Ans) laughing gas is N2O and it is prepared by NH4NO3 (heating it)
Q)Why hydride of oxygen is liquid bt that of sulphur is a gas?
Ans) bcz H-Bonding takes place in case of Oxygen
*****FLOURINE never exists in a +ive oxidation state**********
*****NH3 has higher b. pt than PH3 bcoz of H-Bonding*******
### HF is stored in wax coated glass bottles coz it dont react with wax bt it reacts with glass####
^^^^^IODINE is more soluble in KI than in H20 coz it reacts with KI to form a soluble complex (KI3)
hope this helps.... (a great topic)
good work bhuvana and all others :)
13 Aug 2007 12:25:42 IST
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grp 14 ( c , Si , Ge , Sn , Pb )
1) b.p order : CH4 < SiH4 < GeH4 < SnH4 . why ?
ans - greater the surface area, greater is the vander waal's forces of attraction and higher is the boiling point
2) though CCl4 is not hydrolysed by water , yet it forms COCl2 with superheated steam . why ?
ans - CCl4 is not hydrolysed by water due to non-availability of d orbitals in valence shell of C . but vacant orbitals of higher energy are available with each atom and can be utilised if high energy is provided . so CCl4 reacts with superheated steam to form phosgene.
3) PbCl4 exists . PbBr4 and PbI4 does not . why ?
ans - Cl is a strong oxidising agent and can easily oxidise Pb from +2 oxidation state to +4 . but Br and I are weaker oxidising agents and can't do so.
4) silanes are more reactive than hydrocarbons . why ?
ans - 1) large size of Si than C facilitates attack by nucleophiles
2) greater polarity of Si - X bond ( X = H,C,N,O,F,Cl,I,Br )
3) availability of vacant d orbitals in Si
2) greater polarity of Si - X bond ( X = H,C,N,O,F,Cl,I,Br )
3) availability of vacant d orbitals in Si
5) why tin (II) chloride is solid but tin (IV) chloride a liquid ?
ans- tin (II) chloride is an ionic compound and there exists strong force of attraction between tin and chloride ions and so it is solid .
tin (IV) chloride is covalent in which weak intermolecular forces exists & makes it a liquid.
tin (IV) chloride is covalent in which weak intermolecular forces exists & makes it a liquid.
6) why a piece of tin foil is added to SnCl2 solution for preserving it. ??
ans - SnCl2 hydrolyses in solution to liberate HCl .
SnCl2 + H2O ----> Sn(OH)Cl + HCl
in presence of tin foil , HCl reacts to form SnCl2 again and thus helps in
SnCl2 + H2O ----> Sn(OH)Cl + HCl
in presence of tin foil , HCl reacts to form SnCl2 again and thus helps in
reversing the reaction.
13 Aug 2007 16:03:50 IST
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Patterns in the Periodic Table The periodic table is an arrangement of all the known elements in order of increasing atomic number. The reason why the elements are arranged as they are in the periodic table is to fit them all, with their widely diverse physical and chemical properties, into a logical pattern. If sodium is placed beneath lithium and not next door to fluorine, and potassium is placed beneath sodium to begin another row - and so on - it is found that the vertical lines of elements are chemically similar. These vertical lines are called GROUPS. Horizontal lines of elements are called PERIODS. A set of D-BLOCK ELEMENTS, sometimes called the transition metals, occurs between Groups 2 and 13; these are also chemically similar to each other. Some Groups exhibit striking similarity between their elements, such as Group 1, and in other Groups the elements are less similar to each other, such as Group 4, but each Group has a common set of characteristics. The periodic table is divided into BLOCKS. The s-block elements have valence configuration s1 or s2. The p-block elements have valence configuration s2p1 to s2p6. The d-block elements have valence configurations in which d-subshells are being filled. Hydrogen occupies a unique position at the top of the periodic table. It does not fit naturally into any Group. All the members of a Group have the same valence configuration but different principal quantum numbers. The number of valence electrons equals the Group number. The period number equals the principal quantum number of the valence shell. Chemically, elements in the same block exhibit the same general characteristics. This is most apparent for the s-block elements which are all metals with low electronegativity. The p-block elements are more varied with some metals such as aluminium on the left and non-metals on the right. Between them, indicating the gradual change in character going across the periodic table, are the metalloids (or semi-metals), which lie roughly in a diagonal line from silicon to tellurium. The d-block elements are often called the transition metals, but some of them, such as zinc, do not fit this description well. They are usually considered together as differences between Groups are much less apparent in this block. Periodicity of some properties Periodicity is the name given to regularly-occurring similarities in physical and chemical properties of the elements. Periodicity reflects the periodic repetition of similar electron configurations. Very many properties of the elements show periodicity. The most obvious of these is the continuing change from metal on the left to non-metal on the right. This is reflected in the graph of melting points for the first 20 elements:  For each period the melting point rises from Group 1 to Group 14, then falls to the lowest value at Group 18. If the d-block elements are also included periodicity can be seen between rows of these elements, but as periodicity becomes less apparent with increasing atomic number this is less obvious than for the s- and p-block elements. Variation of first ionisation energy with atomic number also shows striking periodicity. The relative position of each Group in relation to the others follows the same pattern in each period.  Periodicity is also seen for atomic radius and can be summarised by indicating the main trends:  Some chemical properties of the elements also follow trends and can be summarised in the same way. These include bonding, oxidising properties, acid-base properties of the oxides and electronegativity.  |
28 Aug 2007 16:33:14 IST
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grp 15 ( N P As Sb Bi )
1. NCl3 can be hydrolysed .NF3 cant be hydrolysed . Why ?
ans - In NCl3 , Cl has vacant d orbitals to accept lone pair of electrons present on oxygen atom of water molecule.
2. Bond angles of hydrides : NH3 > PH3 > AsH3 > SbH3 .WHY ?
ans - on moving down the group , size of central atom increases and electronegativity decreases . so the bond pair of electrons tend to lie away from central atom.
3. b. p . of NH3 > PH3 and AsH3 . but lower than SbH3 & BiH3 .
ans - becoz hydrogen bonding in NH3 predominates over van der waals forces upto As . but b.p of NH3 is lower than SbH3 & BiH3 .This is bcoz molecular size increases down the group. due to large surface area , van der waals forces predominates over h-bonding.
4. NF3 is stable but remaining trihalides of N are not . why ?
ans - due to low N-X bond energy on account of large difference in size between N and X .
29 Aug 2007 19:04:26 IST
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grp 15 continued .....
1. NF3 has no tendency to act as a ligand. why ?
ans - bcoz the dipole moment due to 3 N-F bonds is in opposite direction to that due to the lone pair of electrons on N . thus it doesn't act as a ligand as lone pair of electron on nitrogen is not freely available.
2. on being slowly passed through water PH3 forms bubbles but NH3 dissolves. why ?
ans- NH3 forms H-bonds with water and dissolves. but PH3 doesn't and escapes out.
3. Ammonia is used as a refrigerant and in ice factories .why?
ans- presence of strong H-bonding in liquified NH3 , it has very very large latent heat of vapourization and remains in the liquid state as it doesn't vapourize easily.
4. NO is paramagnetic in gaseous state but diamagnetic in liq. and solid states . why ?
ans - NO has odd number of electrons (15) in the gaseous state .but in the solid and liq . states , it forms a dimer and doesn't contain unpaired electrons.
21 Feb 2009 22:17:58 IST
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Okay few more....
**Only in OF2(i.e.with fluorine).....O.S. of oxygen is +ve ;rest always -ve...
**[AlF6]- is formed but [BF6]- is not formed...
coz Boron does not hav d orbital 2 expand its octet...
**Same way PCl5 is formed but NCl5 isn't.....
**Distinctive properties in size...
Ga > Al & Tl > In (due 2 poor shieldind effect of d & f-orb. electorns..)
**Solution of borax in H2O is BASIC....why??
brks into.... NaOH + H3BO3 (As NaOH is strong electrolyte..it dissociates completely forming Na+ & OH- 2 give basic sol.n)
21 Feb 2009 22:43:24 IST
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**When NaBr is treated with concentrated H2SO4 ,gives Br2 gas but when NaCl is heated with concentrated H2SO4, HCl is produced. Why?coz Br- is better reducing agent than Cl-.....& it can easily reduce H2SO4 to SO2 & get oxidised itself...bul Cl- can't...(same fr iodide also i.e they r gud reducing agents) **Graphite is the most stable form of carbon.....Its enthalpy of formation is thus ZERO.... **BH3 exists as a dimer (B2H6) but BCl3 does not....why??coz of the backdonation property in BCl3 which is not +nt in BH3.... **Why bond angle decreases....... NH3 > PH3 ...etc..??coz N is more electro-ve than P....their is gr8ter bond pair-bond pair repulsion in NH3 thus gr8ter angle...This trend continues dwn the group... **What is Caro's acid..??H2SO5 is called caro's acid...here O.s of sulphur is +6 & not +8 as might seem frm the mol. formula....It depends on the structure....
23 Feb 2009 17:37:10 IST
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I didn't mean only "OF2"..... i meant 2 say compounds "like" OF2 where Oxygen is with fluorine...show Positive Oxidation states of oxygen....
With other elemnts O always has -ve Oxid. states.....as only Fluorine is more electro-ve than oxygen....
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3) B-X bond length in BX3 is shorter than theoretically expected . why ?
4) on moving down a group , size is expected to increase. then why radius of Ga < Al ?
Ans - this is due to filling of electrons in d-orbitals. in between Al and Ga there are 10 elements having electrons in d orbitals . as d orbitals are large in
5) why boron has a high m.p ???
6) B doesn't form ionic compounds . why ?
7) boron halides do not form dimers . why ?
8) trihalides of grp 13 fume in moist air . why ?
MX3 + 3H20 -> M(OH)3 + 3HX
9)TlCl is more stable than TlCl3 in aqueous solution .why ?
ans - due to inert pair effect