The Student Room Group

Scroll to see replies

is everyones in the afternoon?
Reply 2161
Original post by reneetaylor
You're right! I'll include that definitely, thanks :smile:

You can just say propene.
Reply 2162
Can I have some predictions please guys?


Posted from TSR Mobile
Original post by mari_lynne
hey guys could anyone help explaining to me bond enthalpy questions? when you have to work out the bond enthalpy of a molecule knowing normally the products and △H, would be so appreciated! :smile:


Do you have an example of a question?
Reply 2164
Original post by ii-mohsin-ii
is everyones in the afternoon?



I am assuming so. :smile:


Posted from TSR Mobile
Original post by greenmind
Help urgently needed on how to answer question 6 from the Jan'12 paper
Untitledfdsf.png
Untitledfadfdf.png

Link to the markscheme is http://www.ocr.org.uk/Images/59185-mark-scheme-unit-f322-chains-energy-and-resources-january.pdf


46
CH2OH+
C3H7O

(63x72.2) + (65x27.8)
__________________ = 63.6 which is CU
100
Reply 2166
Original post by simifeltham
ch3ch2ch2oh ---->
h2so4 reflux

ch3ch2ch2oh + 2[o] -----> ch3ch2cooh + h2o

CH3CH2CH2I + KOH------->
(edited 10 years ago)
Say if you are given the molecular formula, how do you find the empirical formula from this? Thanks in advance :smile:
Original post by greenmind
Help urgently needed on how to answer question 6 from the Jan'12 paper
Untitledfdsf.png
Untitledfadfdf.png

Link to the markscheme is http://www.ocr.org.uk/Images/59185-mark-scheme-unit-f322-chains-energy-and-resources-january.pdf


i) m/z value of the peak furthest to the right
ii) a formula which Mr adds up to 31, then just add + to end of that fragment (due to loss of electron)
iii) compound containing C, H, O which Mr adds up to 46 (molecular ion value)
b) (63x72.2)+(65x27.8)/100
Reply 2169
can someone help meee... I just wanna know I get confused when it comes to curly arrows how do I know if its an nucleophile substitution or electrophilic.....please help thanks
Original post by Hello...
ch3ch2ch2oh + 2[o] -----> ch3ch2cooh + h2o


that would be k2cr2o7/h+

with h2so4 and reflux it's dehydration so its CH3CH=CH2 + H2O
Reply 2171
Original post by geekD96
can someone help meee... I just wanna know I get confused when it comes to curly arrows how do I know if its an nucleophile substitution or electrophilic.....please help thanks


If it involves adding things to a double bond to break the double bond, it's electrophillic
It's nucleophillic if it involves swapping OH for a Halogen
Original post by geekD96
can someone help meee... I just wanna know I get confused when it comes to curly arrows how do I know if its an nucleophile substitution or electrophilic.....please help thanks


nucleophile is an electron rich species that can donate a lone pair of electrons such as OH-
Electrophilic is the one such as the addition of HBr or Br2 across a double bond
Reply 2173
Original post by Ché.
Well!?
113 would be around the mid/high 70s...
120 is for an A; that will be around 80 or so...
:biggrin:


Posted from TSR Mobile

Okay that's doable, thanks
Reply 2174
Original post by simifeltham
that would be k2cr2o7/h+

with h2so4 and reflux it's dehydration so its CH3CH=CH2 + H2O

Damn, just made the connection because H2SO4 is used in oxidising alcohols as well as K2Cr2O7
State four ways in which polymers are disposed?
Reply 2176
Original post by simifeltham
nucleophile is an electron rich species that can donate a lone pair of electrons such as OH-
Electrophilic is the one such as the addition of HBr or Br2 across a double bond


oh so if it gives us something like this (this is completely made up) ...................... c4h7I reacting with OH- to give C4H7OH+I- is electrophilic?
Original post by Hello...
Damn, just made the connection because H2SO4 is used in oxidising alcohols as well as K2Cr2O7


yeah that's why I always use just H+ on K2Cr2O7 so I don't get confused with other reactions
Original post by CA$H KRAZE
Say if you are given the molecular formula, how do you find the empirical formula from this? Thanks in advance :smile:


Empirical formula is just the simplest whole number ratio of the molecular formula... so an example of molecular formula... C3H6 simplifies down to CH2 but numbers that dont simplify down... C3H7 the molecular formula for this is the same as the empirical because it wont simplify without creating decimals :smile:
Original post by geekD96
oh so if it gives us something like this (this is completely made up) ...................... c4h7I reacting with OH- to give C4H7OH+I- is electrophilic?


C4H7I + OH- ---> C4H7OH + I- and it's nucleophilic because the OH- is an electron rich species due to the minus sign. it's negatively charged because it can donate a pair of electrons.

Latest