h2 a level chem p3

Z een SG

hm, i know its late, but im just curious to the ans to this question in chem p3.

methylbenzene requires conc sulfuric and nitric acid and 30 degrees celsius to undergo nitration whereas phenol only requires dilute nitric acid.

Give a reason for the difference in conditions and reagents.

Thank you! :)

UltimaOnline SG

2009 ‘A’ Level Exam Qn.

Methylbenzene requires concentrated sulfuric(VI) and nitric(V) acids and 30 degrees celsius to undergo nitration whereas phenol only requires dilute nitric acid. Give a reason for the difference in conditions and reagents.

Solution :

Phenolic hydroxy group is electron donating by resonance and is hence a strong activator, enriching the pi electron density of the benzene ring, making it a much stronger nucleophile (than ubsubstituted benzene). Hence only dilute nitric(V) acid is required for electrophilic aromatic substitution and nitration to occur.

Methyl group is electron donating by induction (and hyperconjugation) and is hence a weak activator, only slightly enriching the pi electron density of the benzene ring, making it only a slightly stronger nucleophile (than ubsubstituted benzene). Hence a nitrating mixture of concentrated nitric(V) and sulfuric(VI) acids are required to generate the nitronium cation (NO2+) for electrophilic aromatic substitution and nitration to occur.

arxoz SG

Generally, why do u all think abt the paper 3?

I think it was kinda easy compared to last year's paper 3. Nevertheless, there were some tricky qns.

absol SG

last yr paper 3 easier T.T

sian.

tut4nkh4m3n SG

question 5 was v easy. the rest were average.

i didn't do question 3, apparently the last part was difficult.

Sputnik159 SG

question 3 last part just take 1 divided by the time lor to get the rate. The rate is 1 1 0 something like that

Barani SG

H2 Chemistry A lvl 2009 question...

Zn(OH)2 plus excess NH3...dissolves to form a complex...write an equation

can the eq be like this?---Zn(OH)2 + 6NH3 --->> [Zn(NH3)6]2+ + 2OH minus

I dun think it's in our syllabus that we need to know how many of the NH3 ligands will be binded to the central transition metal cation...Do you think well be penalised for writing the products as [Zn(NH3)6]2+ instead of the real answer (researched from the net) [Zn(NH3)4] ???

Also, can I define co-ordination no. this way?

Co-ordination no. is the no. of ionic bonds an ion in the lattice structure forms with its surrounding ions..

arxoz SG

Your defn of coordination no. is right. http://en.wikipedia.org/wiki/Coordination_number

And i dun think you will be penalised for writing the complex as [Zn(NH3)6]2+ instead of [Zn(NH3)4] cos its not in our syll to noe it.