Chemistry: MCQs!

[abcde]

AOA!
I need help with this MCQ.
When an animal fat is boiled with aqueous sodium hydroxide, a soap and glycerol are formed. This reaction is an example of
A Esterification
B Fermentation
C Hydrolysis
D Polymerisation

What is the correct option and why? I'm sure that this is neither esterification nor fermentation but the last two options confuse me.

 

[XPFMember]

Re: Chemistry: Macromolecules

Waalaikumassalam!!

It's C....alkaline hydrolysis of fats give the produccts stated

 

[abcde]

Re: Chemistry: Macromolecules

Another MCQ though it's not related to macromolecules:
A student carries out 3 tests on a gas X
1. Damp red litmus paper: stays red
2. Aqueous bromine: stays brown
3. Lighted splint: gas burns
Which gas is X ?
A Ammonia
B Ethene
C Methane
D Oxygen

Again, I'm very sure that X ain't ammonia or ethene. But I don't know whether it's methane or oxygen :?

 

[XPFMember]

Re: Chemistry: Macromolecules

Assalamoalaikum!!

i think it's D...cuz of the result in test 3...but i'm nt sure...so ppl correct me if im wrong!

 

[abcde]

Re: Chemistry: Macromolecules

I also think it's D because oxygen relights a glowing splint but then methane is a fuel and could also do that :S Ethene and Ammonia are out of the question because ethene would decolourise bromine and ammonia would turn the litmus paper blue.

 

[XPFMember]

Re: Chemistry: Macromolecules

yeah!!

 

[leosco1995]

Re: Chemistry: Macromolecules

Waalaikumassalam!

Actually, I think C would be the answer since a glowing splint would have been used rather than a lighted one for oxygen. Also, I'm fairly sure oxygen can't burn on its own. I'm not so sure, but that's what I think..

Well, this question is apparently from June 2004 (Q38) and the marking scheme says it's C.

 

[abcde]

Re: Chemistry: Macromolecules

Oh I think I got it. Thank you very much leosco1995
But what exactly is the difference between a lighted splint and a glowing splint?

 

[Nibz]

Re: Chemistry: Macromolecules

For the first MCQ.. it's saponification (hydrolysis of fats).. and the products of saponification are fatty acids; and three OH alcohol gropus, i.e, Glycerol! So its C!

and the second MCQ would definitely be "Methane".. as it will surely burn in a lighted splint!!
Who says that oxygen itself burns in a lighted splint? :ugeek:

 

[Nibz]

Re: Chemistry: Macromolecules

Oh I think I got it. Thank you very much leosco1995
But what exactly is the difference between a lighted splint and a glowing splint?

"A burning splint has a visible flame at the end while a glowing splint has a glowing ember at its end - (leosco1995)"

Oxygen only rekindles the splint, that is, it brightens its light! The splint would become more intense, not that the gas would burn in it.

 

[abcde]

Re: Chemistry: Macromolecules

So Nibz, soap actually consists of fatty acids?

 

[Nibz]

^ Yes (in a way). The main constituents of soap are Salts of the component fatty acids!

 

[abcde]

Okay

 

[leosco1995]

Re: Chemistry: Macromolecules

But what exactly is the difference between a lighted splint and a glowing splint?

It's very common how these things get muddled up. The test for oxygen is that it relights a glowing splint, while hyrdogen produces a 'pop' sound on a lighted splint. If you write "hydrogen produces a 'pop' sound on a glowing splint" you'll get the answer wrong! A burning splint has a visible flame at the end while a glowing splint has a glowing ember at its end.

 

[CaptainDanger]

Thanks people...

 

[abcde]

I also want to ask why is the displacement of water the first choice for collecting gases? I mean why is a gas's solubility in water considered before its relative density to air?

 

[joelynn]

can pls help me to solve this question ?? paper 9701/1/0/n/02... thx... i stared at dat question... dunno hw 2 start... HELP!!

 

[insomniac]

bcoz there is a high possibility that gas can escape if it is collcted in gas jar . but if the gas aint soluble in water and is a lighter gas it can be collected without impurities by over water delivery .. and gasses like ammonia highly soluble in water method of downward delivery is used as it is a lighter gas and the heavier gases are collected by upward displacement of air ...
(heavier and lighter gases are stated so bcoz of being heavier or lighter than air)

 

[insomniac]

can pls help me to solve this question ?? paper 9701/1/0/n/02... thx... i stared at dat question... dunno hw 2 start... HELP!!

can you please post the link

 

[CaptainDanger]

can pls help me to solve this question ?? paper 9701/1/0/n/02... thx... i stared at dat question... dunno hw 2 start... HELP!!

can you please post the link

I would have.. But I don't get this (9701/1/0/n/02)... Apart from 9701...