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• Flying grenade

  26 Nov 15, 12:26

  Aren't  SO2 and NO harmful gases?

• UltimaOnline

  26 Nov 15, 12:33

  Originally posted by Light5:

  Q: http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w09_qp_42.pdf

  ^Q5 part (a) of the above paper.

  I simply dont know how to solve this part....i do understand that in benzene, all carbons are arranged in trigonal planar compared to cyclohexane but i cant understand how methylpropane is not planar while butane can be planar

  A detailed explanation of how to solve this question would be very helpful. Thank You

  Mark Scheme : http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w09_ms_42.pdf

  
  For the purpose of this question, look only at the C atoms (ignore the H atoms), and bear in mind all single bonds can freely rotate.
• UltimaOnline

  26 Nov 15, 12:34

  Originally posted by Flying grenade:

  Is the cj acid and cj base of H2O, H3O+ and OH- respectively?

  Is the cj base of H3O+, H2O? What would it be its cj acid then?

  
  H4O2+, which doesn't exist due to thermodynamic infeasibility due to excessive instability.
• UltimaOnline

  26 Nov 15, 12:36

  Originally posted by Flying grenade:

  Why higher pressure means less of the species, and

  on the side with greater number of moles of gas?

  Is it because greater number of moles of gas in a fixed vessel volume , there is higher pressure, and since there are greater no. moles of gas, the mole fraction of the gas we're interested in, is smaller, and hence less of the species??

  
  There are 2 ways of looking at this, by Le Chatelier's principle (recommended for A levels) and mathematically (not recommended for A levels). As predicted by Le Chatelier's principle, the system will oppose the change (eg. increased pressure) by shifting to the appropriate side of the equation (eg. less moles of gas).
• UltimaOnline

  26 Nov 15, 12:37

  Originally posted by Flying grenade:

  Aren't  SO2 and NO harmful gases?

  
  Yes. Not replying any more qns liao, until after today's P1 is over.
• ArJoe

  26 Dec 15, 22:36

  Hi, regarding 2007 p3 q3d tys question on asking how to differentiate the 3 carbonyl compounds, can i write 1)add alkaline aqueous iodine to each of the 3 compounds and warm. Methanal will not form a yellow precipitate whereas propanone and ethanal will. 2) to distinguish between ethanal and propanone, add tollen reagent to each compound sepaeately and silver mirror will be observed for ethanal but not for propanone? Thanks! The tys answer wrote add tollen reagent first then use alkaline aqueous i2 to differentiate between methanal and ethanal. So is my answer acceptable?
• ArJoe

  26 Dec 15, 22:39

  And for tys 2008 p2 q1c is it alright to just write amine, alcohol and phenol imstead of spedifying primary amine secondary alcohol?
• UltimaOnline

  26 Dec 15, 22:51

  Yes, acceptable. No, you must specify pri vs sec vs tert.
• ArJoe

  26 Dec 15, 22:54

  Hi,just asking if the cs toh a level study guide is sufficient for the h2 chem syllabus? Because some stuff like sn1 and sn2 mechanism are missing...
• UltimaOnline

  27 Dec 15, 01:02

  Originally posted by ArJoe:

  Hi,just asking if the cs toh a level study guide is sufficient for the h2 chem syllabus? Because some stuff like sn1 and sn2 mechanism are missing…

  
  SN1 and SN2 are included in CS Toh's updated A level study guide. How many years back did you buy your A level study guide?
• ArJoe

  27 Dec 15, 12:16

  Tys 2013 paper 2 qn 2a) the part asking the effect of increasing temp and pressure on partial pressure of co equilibrium My answer is: le chatelier principle state that when a system in equilibrium is subjected to a change, the system wil attempt to counteract the change and to reestablish its equilibrium state. According to lcp, when temperatuee increases, the system will attemptto reduce the overall temperature by favouring the endothermic reaction. Since forward reaction is endothermic, forward reaction is favoured and position of equilibrium shifts to the right, producing more co and hence amount of co increases at equilibrium. Since partial pressure of co is proportional to the amount of co, partial pressure of co increases. according to lcp, when pressure increases, the system will attempt to decrease the overall pressure of the system by favouring the reaction that produces less gaseous molecules. since reverse reaction produces less gaseous molecules, reverse reaction is favoured , decreasing the amount of co produced at equilibrium. since partial pressure of co is proportional to amount of co, partial pressure of co decreases at equilibrium. Is my answer correct? Thanks!
• ArJoe

  27 Dec 15, 12:18

  And yes i accidentally borrowed the 2007 cs toh a level guide from my jc library... so it is not updated
• ArJoe

  27 Dec 15, 12:27

  And does acid base neutralisation of phenol/ carboxylic acid and na+phenol/carboxylic acid/ alcohol requires heat? Or does room temperature works also
• UltimaOnline

  27 Dec 15, 15:45

  Originally posted by ArJoe:

  Tys 2013 paper 2 qn 2a) the part asking the effect of increasing temp and pressure on partial pressure of co equilibrium

  My answer is: le chatelier principle state that when a system in equilibrium is subjected to a change, the system wil attempt to counteract the change and to reestablish its equilibrium state. According to lcp, when temperatuee increases, the system will attemptto reduce the overall temperature by favouring the endothermic reaction. Since forward reaction is endothermic, forward reaction is favoured and position of equilibrium shifts to the right, producing more co and hence amount of co increases at equilibrium. Since partial pressure of co is proportional to the amount of co, partial pressure of co increases.

  according to lcp, when pressure increases, the system will attempt to decrease the overall pressure of the system by favouring the reaction that produces less gaseous molecules. since reverse reaction produces less gaseous molecules, reverse reaction is favoured , decreasing the amount of co produced at equilibrium. since partial pressure of co is proportional to amount of co, partial pressure of co decreases at equilibrium.
  Is my answer correct? Thanks!

  
  Yes, your answer is fine. But the statement "since partial pressure of co is proportional to amount of CO, partial pressure of co decreases at equilibrium" is redundant. You could have simply said, "... since reverse reaction produces less gaseous molecules, reverse reaction is favoured, hence decreasing the amount and partial pressure of CO produced at equilibrium".
• UltimaOnline

  27 Dec 15, 15:48

  Originally posted by ArJoe:

  And does acid base neutralisation of phenol/ carboxylic acid and na+phenol/carboxylic acid/ alcohol requires heat? Or does room temperature works also

  
  Room temperature for all aqueous Bronsted-Lowry acid-base reactions, as Ea is very low for proton transfers to occur.
  
  In Inorganic Chem, SiO2(s) requires strong heating with concentrated or liquid alkalis to react, due to very high Ea as a result of the giant covalent lattice structure of SiO2(s).
• ArJoe

  27 Dec 15, 21:30

  Thanks for the replies. Really appreciate it. I have another question. Whenever a question ask you to name and describe the mechanism, for example electrophilic substitution, is it necessary for you to write things like generation of electrophile, electrophile attack electron rich benzene ring to form xarbocation intermediate etc, instead of just drawing the mechanism( like show the arrows pointing from electron rich benezene ring to the elecrrophile etc) because my teacher told me that drawing the mechanism is sufficient, and it is redundant to describe the mechanism. like no need to say generation of electrophile, formation of carbocation etc
• UltimaOnline

  28 Dec 15, 06:18

  Originally posted by ArJoe:

  Thanks for the replies. Really appreciate it.
  I have another question. Whenever a question ask you to name and describe the mechanism, for example electrophilic substitution, is it necessary for you to write things like generation of electrophile, electrophile attack electron rich benzene ring to form xarbocation intermediate etc, instead of just drawing the mechanism( like show the arrows pointing from electron rich benezene ring to the elecrrophile etc) because my teacher told me that drawing the mechanism is sufficient, and it is redundant to describe the mechanism. like no need to say generation of electrophile, formation of carbocation etc

  
  Correct. Just draw the full mechanism, is what Cambridge requires. If they require you to write something in words, the question will ask for it separately.
• ArJoe

  29 Dec 15, 10:53

  Hi, for h2 chem, is it alright to just write heat for all the organic reactions that require heating instead of heat under reflux. Because the tys answers wrote heat under reflux, whereas my school notes write heat or reflux. thanks!
• Kinnagao

  29 Dec 15, 11:14

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• ArJoe

  29 Dec 15, 11:33

  Originally posted by Kinnagao:

  Hello    

  I am Kinna from Shenzhen Xinwangyuan Technology Co., Ltd

  We produce and sale all kinds of precision fasteners include bolts & nuts, standoffs, rivets, studs, screws; precision lathe parts; machining parts, PEM nuts ;cabinets, and sheet metal products, etc.

  Can custom as customers drawing desgin or samples.  Can do ODM OEM Service. ☆SUNWAND☆

   

  If you are interested in  ,weclome to contact me do business or become friends .  

   

   

  
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• UltimaOnline

  29 Dec 15, 13:12

  Originally posted by ArJoe:

  Hi, for h2 chem, is it alright to just write heat for all the organic reactions that require heating instead of heat under reflux. Because the tys answers wrote heat under reflux, whereas my school notes write heat or reflux. thanks!

  
  Some cases, either alone is acceptable. Some cases, only heat is acceptable. Some cases, heating under reflux is required.
  
  Any of these books are reliable (ie. you can safely follow what they write) : CS Toh, Chan Kim Seng & Jeanne Tan, George Chong. Better yet, you should get and use all 3 books (total of 5 books, since other than CS Toh, the other books come in 2 parts : Phy/Inorg and Org).
• ArJoe

  29 Dec 15, 13:53

  Is the organic and inorganic chemistry summary book by pang peng cheong and sam lee reliable? They wrote heat
• ArJoe

  29 Dec 15, 13:55

  Cs toh guide book wrote heat or reflux too
• ArJoe

  29 Dec 15, 14:12

  So basically according to cs toh guide book, 24dnph and iodoform test write warm, esterification using alcohol and carboxylic acid write heat under reflux, acid hydroysis of esters and nitrile group write heat under reflux... so follow this?
• UltimaOnline

  29 Dec 15, 15:48

  Originally posted by ArJoe:

  So basically according to cs toh guide book, 24dnph and iodoform test write warm, esterification using alcohol and carboxylic acid write heat under reflux, acid hydroysis of esters and nitrile group write heat under reflux… so follow this?

  
  Yes, just follow CS Toh is safe.