A level chemistry :Organic
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After 2 days struggling with Maths,now, I came back to chemistry.
Still not understand your solution in transformation excercise. Can you write in that style? For example : Ankaline + cl => Halogen deravetives... etc
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Originally posted by UltimaOnline:
For such dual-purpose, the following book is unrivalled :
For the complete list of textbooks and guidebooks I recommend for Singapore-Cambridge A Levels H2 Chemistry, see my webpage :
http://infinity.usanethosting.com/Tuition/#Books_for_H2_Chemistry
Hi ultima,
This book you recommended, are you aware if it provides solutions for the "My Tutorial" questions found at the end of each chapter?
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Originally posted by atomos:
Hi ultima,
This book you recommended, are you aware if it provides solutions for the "My Tutorial" questions found at the end of each chapter?
Hi Atomos, no, the end-of-chapter "My Tutorial" questions do not come with solutions. This is because the authors intended to use these questions for their own RJC tutorials, assignments, tests and exams. The authors are no longer at RJC; both of them are now currently teaching at another (two different) JCs.Just tell your students to skip the end-of-chapter "My Tutorial" questions; even without these questions, these two books come with a wealth of Practice Qns that do come with Worked Solutions, within each chapter.
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Originally posted by Theplayfulgirl brainy:
After 2 days struggling with Maths,now, I came back to chemistry.
Still not understand your solution in transformation excercise. Can you write in that style? For example : Ankaline + cl => Halogen deravetives... etc
No sorry, I only give brief guidelines, I do not give complete worked solutions. Ideally, you should hire a personal tutor to help you in the few weeks you have left before your NTU entrance exam.But if you're on a tight budget, I recommend you just focus on the worked examples in CS Toh's A level practice questions (both MCQ and Structured), which are very cheaply available, even if you're on a tight budget. Links to buy them from CS Toh's website are given on my website :
http://infinity.usanethosting.com/Tuition/#Books_for_H2_ChemistryIt's true that your NTU exam does cover a little beyond the A levels, but it would be prudent and practical for you to just focus on the A level syllabus : if you do well enough in the A level syllabus, you can skip the beyond-A-levels part of your NTU exam, and perform more than sufficiently well to clear your NTU entrance exam.
and
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Can you help me to draw VSEPR of IF3
P/s: Is it now in Singapore the Lunar New Year.
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Originally posted by Theplayfulgirl brainy:
Can you help me to draw VSEPR of IF3
P/s: Is it now in Singapore the Lunar New Year.
Chinese Lunar New Year celebrations/traditions/activities span over several days, with pre-celebrations beginning as early as today (for some people/schools/organizations/businesses), and (non-holiday) celebrations/traditions/activities continuing on for over a weeks (for some people/schools/organizations/businesses).Chinese New Year falls on Sunday 10 February 2013 and Monday 11 February 2013, the next day, Tuesday 12 February 2013, will be a public holiday.
IF3 molecule has central I atom with 2 lone pairs, 3 bond pairs; since ionic charge (which is "sum of formal charges") for a neutral molecule is 0, and safely taking the F atoms to have 3 lone pairs 1 bond pair and thus having 0 formal charge, accordingly the I atom, already having 3 bond pairs with the F atoms, must have 2 lone pairs in order to satisfy having a formal charge of 0.
The correct technique for drawing structures in chemistry is all about understanding formal charges.
Hence electron geometry with 2 + 3 = 5 electron charge clouds = trigonal bipyramidal.
Since 2 of the electron charge clouds are lone pairs, which prioritically occupy the equatorial positions (to maximize stability by minimizing lone pair - lone pair repulsions), hence the molecular geometry of IF3 is T-shaped.
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How about its Lewis structure?
P/S: Happy Lunar New Year. It is the same in my country now -
Originally posted by Theplayfulgirl brainy:
How about its Lewis structure?
P/S: Happy Lunar New Year. It is the same in my country now
Strictly speaking,Displayed Structural Formula (as opposed to empirical, molecular, skeletal or condensed structural formulae) may be drawn in the form of :
a Lewis diagram = Dot and Dot structure
a Kekule diagram = Line and Dot structure
a Dot and Cross diagram = Dot and Cross structure
Many people, including teachers in Singapore JCs, are confused about the difference between these terms, and often use the term "Lewis structure" when they mean "Kekule structure"; Cambridge uses the term "Displayed Structural Formula".
For 'A' level purposes, Cambridge will accept any of the above, or even hybrid variants between.
So the Lewis or Kekule or Dot & Cross structure is simply (any of the following, but the left-most diagram is preferred) :
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Hm. I want the Lewis structure of IF3 because I wonder that whether F can borrow only 1 e from I ? Can you draw it in dot-dot Lewiss
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Originally posted by Theplayfulgirl brainy:
Hm. I want the Lewis structure of IF3 because I wonder that whether F can borrow only 1 e from I ? Can you draw it in dot-dot Lewiss
In terms of formal charge, F didn't 'borrow' any electrons. Its 3 lone pairs are its own, and half of its bond pair belongs to F, the other half belongs to I. For formal charge, 3 lone pairs and 1 bond pair = 7 valence electrons, thus F has no formal charge.In terms of stable octet, F and I share both electrons in the bond pair, so the F atoms have a stable octet, while the I atom has an expanded octet. For stable octet, 3 lone pairs and 1 bond pair = 8 valence electrons for F, and 2 lone pairs and 3 bond pairs = 10 valence electrons for I, which has vacant, energetically accesible orbitals to accomodate an expanded octet.
In terms of oxidation state, which is formal charge + electronegativity consideration, for every I-F bond present, the I atom loses 1 electron, and each F atom gains 1 electron. Afterall, that's the definition of electronegativity, the capacity to attract electrons due to effective nuclear charge. I has 0 formal charge, but 3 bond pairs with more electronegative F atoms, and hence the OS of the I atom is 0 + +3 = +3. The OS of each F atom is 0 (formal charge) + -1 (electronegativity consideration) = -1.
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Hm. But a element can borrow only 1 electron or they have to borrow 2
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In terms of stable octet, or formal charge, or oxidation state?
If you don't understand what these terms mean, it's difficult to help you further on this qn online.
Tuition would be an ideal learning environment for teaching such concepts properly. An online forum is not.
Google out these terms online, and re-read my previous post, see if you can understand them better after googling out these terms.
If anyone reading this thread would like to reply to the TS with your own way of explaining, feel free to do so.
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Hi!
I am back. Well. Now, i have problem with the term" disproportional reaction''. Could you explain for me?
Btw, in my book. they mention about the reaction of CH3CO- or CH3CH(OH)- with I2/NaOH but they only give me the example about CH3CHO and CH3CH2OH, which make me hard to understand rationally. I cannot find any rule from it. What is the reaction between CH3COCH3 with I2/NaOH
Thank you
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Originally posted by Theplayfulgirl brainy:
Hi!
I am back. Well. Now, i have problem with the term" disproportional reaction''. Could you explain for me?
Btw, in my book. they mention about the reaction of CH3CO- or CH3CH(OH)- with I2/NaOH but they only give me the example about CH3CHO and CH3CH2OH, which make me hard to understand rationally. I cannot find any rule from it. What is the reaction between CH3COCH3 with I2/NaOH
Thank you
http://en.wikipedia.org/wiki/Disproportionation---------------------------------------------
http://www.chemguide.co.uk/organicprops/carbonyls/iodoform.html
http://en.wikipedia.org/wiki/Iodoform
http://en.wikipedia.org/wiki/Haloform_reaction
The key to understanding any organic chemistry reaction, is its mechanism :
http://www.organicchem.org/oc2web/lab/exp/oxid/iodoform.pdf
http://www.organic-chemistry.org/namedreactions/haloform-reaction.shtm
http://www.demochem.de/D-Iodof-e.htm
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ah ha. How about the reaction between Halides and Ch3COOH. It isn't mentioned in Step by step but in your link so I want to know it.
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Originally posted by Theplayfulgirl brainy:
ah ha. How about the reaction between Halides and CH3COOH. It isn't mentioned in Step by step but in your link so I want to know it.
No iodoform generated. Under alkaline conditions, carboxylic acids are deprotonated, generating carboxylate ions, which are thus anionic, rendering the alpha C's protons non-acidic.The first step of the iodoform mechanism (for methyl ketones; for methyl alcohols there is an additonal prior step which oxidizes the methyl alcohol to methyl ketone) involves alpha deprotonation of the methyl ketone's alpha protons (by the OH- base) to generate the enolate ion nucleophile, which subsequently attacks the diiodine electrophile.
This substitution of the alpha protons with iodine atoms repeats itself until the CH3 group becomes the CI3 group, which is a far better leaving group because CI3- anion has a much lower charge density compared to the CH3- anion.
The penultimate step involves the OH- nucleophile attacking the methyl ketone's acyl/carbonyl C atom, eliminating CI3 as CI3-. The final step involves a proton transfer from the (newly generated) carboxylic acid, to the CI3-, generating the yellow precipitate of triiodomethane (aka iodoform).
However (considering the first step of deprotonation), if you were to use a methyl carboxylic acid (instead of a methyl alcohol or a methyl ketone), a dinegative anionic charge on the conjugate base is simply too destabilizing. Hence methyl carboxylate ions cannot be further deprotonated, and therefore the iodoform reaction cannot proceed with methyl carboxylic acids.
Methyl amides and esters, also do not undergo the iodoform reaction, because the carbonyl O atom already bears additional electron density by resonance (as the O atom of the ester, or N atom of the amide, already donates its lone pair by resonance to the carbonyl group). Hence methyl esters and amides also (like carboxylate ions), are unable to be further deprotonated, and therefore unable to undergo the iodoform reaction.
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What do you think about this question:
Find Hf of AgI, explain why Hf Br2 is positive
AgI + 1/2Br2=> AgBr +1/2 I2 delta H =a
Hf AgBr =a
Hf Br2 =b
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Originally posted by Theplayfulgirl brainy:
What do you think about this question:
Find Hf of AgI, explain why Hf Br2 is positive
AgI + 1/2Br2=> AgBr +1/2 I2 delta H =a
Hf AgBr =a
Hf Br2 =b
I think this question is poorly set, you should skip it.Standard enthalpy of formation of any element under standard conditions is defined as zero.
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Yes, the zero stuff is the only thing I need