IIT-JEE problems

[Jaskanwar Singh]

guys shouldnt there be a thread where we can discuss several questions sometimes with each other? we can try to solve each others problems.

when replying to questions put answers in spolier tags. so that others dont want to see it.

 

[Ishu Gupta]

Sure.
Include AIEEE too.

 

[Jaskanwar Singh]

yes yes sure. all problems of different levels.

some questions i dont know -
1. alkali metals are paramagnetic but their salts are diamagnetic. explain.
2. why ammonia has higher melting point than phosphine?

answer them fast please. my XI chemistry exam on monday.

 

[abhijangda]

alkali metals are paramagnetic
They are paramagnetic because they have one unpaired electron.
Take the case of Sodium, it's atomic number is 11. so its configuration is [Ne] 3s1. Hence one unpaired electron will make it paramagnetic.
And their compounds are diamagnetic because they have no unpaired electron in their compounds.
And for last question
Dipole moment of Ammonia is greater than that of Phosphine or you can say that as Nitrogen is more electronegative than Phosphorus so Nitrogen-Hydrogen bond is more polar than Phosphorus-Hydrogen bond which increases the forces between two atoms.

Best of Luck for exams, also feel free to ask!!

 

[Jaskanwar Singh]

Thanks buddy. Also for 2nd one hydrogen bonding can be considered then i suppose?

 

[pauldmps]

^^ Both NH3 & PH3 have polar molecules. But N is much more electronegative than P. Hence NH3 has intermolecular hydrogen bonding while PH3 has only dipole-dipole forces.

 

[abhijangda]

Thanks buddy. Also for 2nd one hydrogen bonding can be considered then i suppose?

Yes why not!!

 

[Jaskanwar Singh]

thanks everyone.

BTW what will be the structure of NNO. N'triplebond'N'coordinatebond'O?

 

[ssk_the_gr8]

god..... how i hated all of this....
best of luck ... all of you'll

 

[pauldmps]

^^ Actually, there are two resonating stuctures: One you mentioned while another is N=N=O

 

[Jaskanwar Singh]

ok thanks.

why is there + overlap hybrid orbitals? i mean why + lobes overlap?

 

[abhijangda]

ok thanks.

why is there + overlap hybrid orbitals? i mean why + lobes overlap?

sorry, but i cant understand your question. Did you mean why is there positive overlap hybrid orbitals or anything else??

 

[Jaskanwar Singh]

Like why +ve lobes of hybrid orbitals are large and overlap with other elements' p or s orbitals etc? Why -ve lobes are small?

 

[abhijangda]

Like why +ve lobes of hybrid orbitals are large and overlap with other elements' p or s orbitals etc? Why -ve lobes are small?

See, you know that lobes represents electron density or probability of finding an electron around nucleus. Lets take example of CH4 it has 4Hydrogen and one Carbon. This Carbon has 2p orbitals which has +ve and -ve lobes. When s-orbital is attached with +ve lobe then the final hybrid orbital lobe becomes large because probability of finding electron there increase and when s orbital combines with -ve lobe then it decreases because probability of finding electron there decreases.

 

[Jaskanwar Singh]

paper went good. thank you. now english

 

[Zangetsu]

all r students here?

study hard.

 

[Jaskanwar Singh]

Btw solubility of alkaline earth metal carbonates decreases down the group?

And why is KO2 paramagnetic?

 

[pauldmps]

^^ 1. Size of cations & hydration enthalpy increases down the group, hence solubility decreases.

2. It has one or more unpaired electrons (duh!)

 

[Jaskanwar Singh]

^^i know it will be beacuse of unpaired electrons!!. but i am asking for electronic config or some explanation to write in exam.

 

[abhijangda]

all r students here?

study hard.

i m not a 12th or 11th student.

@jaskanwar: KO2 contains super oxide ion. Write configuration of super oxide ion according to Molecular orbital Theory and u will get an unpaired electron