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Wednesday, July 22, 2020
Metallurgy- Extraction of elements, and purification methods:
Tuesday, July 21, 2020
Decomposition of H2O2 follows a first order reaction. In fifty minutes the concentration of H2O2 decreases from 0.5 to 0.125 M in one such decomposition. When the concentration of H2O2 reaches 0.05 M, the rate of formation of O2 will be : [JEE MAINS 2016]
Monday, July 20, 2020
What are Zeeman and Stark effects? Were they explained by the Bohr’s theory?
Ionization energy of Boron is smaller than Beryllium even though effective nuclear charge is higher?
The
electronic configurations of Boron and Beryllium are (5B=1S2,2S2,2p1)
and (4Be =1S2,2S2).
In Boron the
outermost electron is present in the 2p orbital (low penetration power) and is
less strongly bound than the electron present in a 2S orbital of Beryllium (Have
more penetration power), which will has a higher Zeff. It is easier to ionize
the Boron atom.
(1) What are the Amphoteric metals ? gives Examples.
(2) Name of total metalloids present in periodic table ?
(3) Total numbers of elements which are liquid at normal temperature is ?
(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.
(5) What is atomic density ? give the periodicity of atomic density in periods and groups.
(6) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?
(7) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.
(8) In alkali metal group which is the strongest reducing agent in aqueous solution and why?
(9) The electron affinity of sulphur is greater than oxygen. Why?
(10) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.
(11) The electronegativities of B, Al, Ga are 2.0, 1.5, 1.6 respectively. The trend is not regular. Explain.
(12) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.
(13) Of all noble metals, gold has got a relatively high electron affinity. Explain.
(14) What are the increasing order of ioni radii of first group elements in water ?
(15) What are the increasing order of molar conductivity of first group elements in water ?
The complex formation Tendency of NH3 is wisher than PH3.
What happens if two deactivating and one activating group is present on a benzene ring?
What is bromoform reaction?
Is Methanal an aldehyde?
Wednesday, July 8, 2020
Which is a better nucleophile, among halides ions ( fluoride, Chloride, bromide and iodide)? and Why?
(2) F⁻ is a better nucleophile than Br⁻ in polar aprotic solvents.
We know that a protic solvent has an H atom bound to more electronegative elements like F, O or N. It can use its H atom to formed H-bonding with a nucleophile. Which accumulate around nucleophilic and creates a shell around the nucleophile. So that it becomes more difficult to attack the positive carbon bearing the leaving group.
F⁻ is a small ion with a high charge density. It is tightly solvated.
I⁻ is a large ion with a low charge density. It is loosely solvated. There are only a few solvent molecules to push out of the way.
Hence over all order of nucleophilicity in polar protic solvents is given as :
[ I⁻ > Br⁻ > Cl⁻ > F⁻ ]
We know that a polar aprotic solvent does not have a hydrogen atom that can formed hydrogen bond.
But in all of them, the negative ends of the dipoles directedaway from the molecule. So that It is easy for them to solvate cations.
The positive ends of the dipoles are closer to the middle of the molecule. It is difficult for them to get close to the anions.
As the result the nucleophile has few molecules in its solvent shell. The nucleophile can more easily attack on positive carbon (electrophilic center).
Hence F⁻ becomes a much better nucleophile than chloride,
Hence over all order of nucleophilicity in polar aprotic solvents is just reverse of that given in polar protic solvent :
[ F⁻ > Cl⁻ > Br⁻ > I⁻ ]