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Thursday, October 4, 2007

Chemistry Questions - Organic Chemistry

Halo,

Came across the following question with my student today and thought you will be interested to give it a try:

Q) Which statement is true for both propene and polypropene?
A) They have identical empirical formulae
B) They are insoluble in organic solvents
C) They have identical molecular formulae
D) They decolourise liquid bromine solution rapidly

Come on O Level students, give it a shot.I understand that lots of you are checking out on this blog. The best way to learn is to Just Do It (like NIKE)! Nothing to be shy about, just share your answer. It is alright if you got it wrong. Failure is the mother of success, still rmbr that?

PS: Thank you "C" for letting me this chance to share the above question.

Cheers
Sean
SimpleChemConcepts

Qn answered and explained under comments

5 comments:

zhengning said...

Heythere, Glad I've got the previous 2 questions right, haha, i will definitely share this site with the rest, really helpful.

I decided to try doing this question too.

The options and how i feel:
A) They have identical empirical formulae

This could be the answer.. Polypropene is formed from propene as a monomer.
The empirical formulae is CH2.

B) They are insoluble in organic solvents

I was taught in school that the first 4 members of alkenes are soluble, hence upon seeing this option, i eliminated it.

C) They have identical molecular formulae

Propene and Polypropene do not have identical molecular formuale.

Propene is given C3H6, while Polypropene is (C3H6)x.


D) They decolourise liquid bromine solution rapidly

Propene has a C=C double bond in it's structure, hence it will decolourise bromine(aq).
However, Polypropene, do not have C=C double bond, as it polymerizes and the bonds 'open up'.

My answer to this question is thus, (A).

Yes/No? :X

Anonymous said...

D!

robobooga said...

i think its also (A)... my reasoning is the same as zhengning... ^_^ hope its correct...

lijun(: said...

i think it's A too..
same reasons as zhengning.

Sean Chua said...

Answer is (A). I will add on some key concepts using Zhengning's answer:

A) They have identical empirical formulae

Polypropene is formed from propene as a monomer.The empirical formulae is CH2.

"Polypropene is an Additional Polymer. For Additional Polymer, not atoms are added or lost. In fact, the double bonds only unfolds, open up and accept other monomer. Thus, addional polymer has same empirical formulae as their monomer. Condesation polymers will be different."

B) They are insoluble in organic solvents

I was taught in school that the first 4 members of alkenes are soluble, hence upon seeing this option, i eliminated it.

"Not sure what your school teacher said, but In fact, all hydrocarbon molecules will be soluble in ORGANIC solvents. This is bcos ORGANIC solvents are also Hydrocarbon in nature. In JC,POLY n UNI - they say "Like dissolves Like""

C) They have identical molecular formulae

Propene and Polypropene do not have identical molecular formuale.
Propene is given C3H6, while Polypropene is (C3H6)x.

"Polypropene is represented as:
CC3H6)n where n represents a large number. I am tying to say that we use n instead of x for representing molecular formulae for polymer."

D) They decolourise liquid bromine solution rapidly

Propene has a C=C double bond in it's structure, hence it will decolourise bromine(aq).
However, Polypropene, do not have C=C double bond, as it polymerizes and the bonds 'open up'.

"Well Done. Good explaination"

Hope this gets you to understand further.

Cheers
Sean
SimpleChemConcepts