• We need your support!

    We are currently struggling to cover the operational costs of Xtremepapers, as a result we might have to shut this website down. Please donate if we have helped you and help make a difference in other students' lives!
    Click here to Donate Now (View Announcement)

AS Chemistry P2 Prep.

Messages
532
Reaction score
151
Points
53
sorry but either u understood it wrong or u wrote it wrong. reflux, i simple words means heating under pressure. for oxidation of alcohol, reflux produces ann ACID!! for aldehyde u have to heat it and distill off the product as soon as it is formed.
this is the definition:
my teacher told me reflux means strong heating....
 
Messages
5
Reaction score
2
Points
3
Did I just read reflux means really strong heating? Guyz, no!

Reflux is when you have to distill something off before the reaction proceeds. FOr instance, while oxidizing an alcohol to get an aldehyde and not an acid,
one should reflux the aldehyde as it is formed so that it doesn't stay in there with the agent and get oxidized further.
Similarly, here, for conversion of nitriles to -COOH acids, you gotta reflux the acid as it's formed!
I'm happy that you noticed that the meaning of reflux as strong heating was wrong, but it's sad to know that even you haven't got it right... Your exam is true to the fact that when you distill , aldehydes form rather then then carboxylic acids. But reflux aids the formation of carboxylic acids ! Basically reflux is the exact opposite of distillation where a condenser is attached on top of the reacting mixture to prevent volatile mixtures from escaping.
 
Messages
211
Reaction score
175
Points
53
Orange or yellow... preferably orange. beware of red; I haven't seen it being used by the Examiners. In book Cambridge-endorsed books and Mark Schemes, they've used orange, or in rarer cases yellow. We have to be careful to use the terms they like; orange is the safest.
nah, orange is safest to write if ur not sure, but i've seen in many mark schemes that u can write orange-red as well. NOT just red, but orange-red.
 
Messages
211
Reaction score
175
Points
53
condition and reagent for hydrolysis of ester?
there are 2 conditions, acid hydrolysis and basic hydrolysis. In acid hydrolysis with HCl for example, after hydrolysis, simply the corresponding carboxyllic acid and alcohol are formed.
But in basic hydrolysis, initially sodium salt and alcohol are formed, but after you reflux it, the sodium salt is also converted to the corresponding carboxyllic acid.
 
Messages
532
Reaction score
151
Points
53
there r 2 diff. hydrolysis of esters...acid hydrolysis...eg warm with acid catalyst, produces alcoholes and -cooh...
but alkaline hydrolysis forms propane-1,2,3-triol and the salts of fatty acids...
 
Messages
99
Reaction score
23
Points
8
I'm happy that you noticed that the meaning of reflux as strong heating was wrong, but it's sad to know that even you haven't got it right... Your exam is true to the fact that when you distill , aldehydes form rather then then carboxylic acids. But reflux aids the formation of carboxylic acids ! Basically reflux is the exact opposite of distillation where a condenser is attached on top of the reacting mixture to prevent volatile mixtures from escaping.
Okay, first, I KNOW that for acids to form u need to reflux.
And a condenser is attached anyhoo (distillation or Reflux!). And no reflux is not the exact opposite of distillation. Here, check this image
http://en.wikipedia.org/wiki/File:Fractional_distillation_lab_apparatus.svg

And see what it reads "Laboratory apparatus using reflux to supply energy to chemical reactions. An Erlenmeyer flask is used as a receiving flask. Here the distillation head and fractionating column are combined in one piece."
 
Messages
99
Reaction score
23
Points
8
"Heating under reflux means heating with a condenser placed vertically in the flask to prevent loss of volatile substances from the mixture"

Thats what it means. More or less, similar to distillation.
 
Messages
532
Reaction score
151
Points
53
"Heating under reflux means heating with a condenser placed vertically in the flask to prevent loss of volatile substances from the mixture"

Thats what it means. More or less, similar to distillation.
then y sometimes even if the condition is to supply heat...ms just write heat/reflux/warm
 
Messages
99
Reaction score
23
Points
8
Because placing the condenser above doesn't matter a difference if the liquids are not volatile. So the student won't be penalized for writing reflux because heating is accompanied with reflux.
 
Messages
438
Reaction score
106
Points
53
then y sometimes even if the condition is to supply heat...ms just write heat/reflux/warm
because heating and reflux heating is not the same thing. Reflux is important when you're tryna make sure, no gases and stuff are lost... but sometimes it's just heating.. providing heat... isn't the process of heat refluxing... so don't think of them the same at all.
 
Messages
13
Reaction score
1
Points
3
"Heating under reflux means heating with a condenser placed vertically in the flask to prevent loss of volatile substances from the mixture"

Thats what it means. More or less, similar to distillation.

Preventing loss of volatile substances would be reflux. Distillation would be something you do after the reaction is complete to separate the reactants and products. No? At least that's what I thought.

I'm asking not telling btw. I'm pretty confused right now.
 
Messages
532
Reaction score
151
Points
53
because heating and reflux heating is not the same thing. Reflux is important when you're tryna make sure, no gases and stuff are lost... but sometimes it's just heating.. providing heat... isn't the process of heat refluxing... so don't think of them the same at all.
so if u just write reflux... then wat does it mean?
 
Messages
532
Reaction score
151
Points
53
Preventing loss of volatile substances would be reflux. Distillation would be something you do after the reaction is complete to separate the reactants and products. No? At least that's what I thought.

I'm asking not telling btw. I'm pretty confused right now.
same here...i never thought that it will become this much confusing?:)
 
Top