Topics 10 & 20

IB Chemistry: Topics 10 & 20

Organic chemistry is one of the bigger topics in terms of time and content. It takes up 11 of the 95 hours of Core time and 23 of the 155 hours allotted to the Core and AHL for Higher Level students. You will need to plan carefully how and when you intend to teach it. There are several different approaches that teachers have used successfully in the past. Some just plough through it as it is set out in the programme....

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Comments 10

Bill Chia 20 February 2018 - 23:34

Hi Geoffrey,

Can I check if the 2,4DNPH test for carbonyls and Tollen's reagent for aldehydes need to be taught for redox reactions in Org. Chemistry? It is not stated clearly in the curriculum.


Paul Lloyd 21 February 2018 - 07:37

Hi Bill
Geoff is away in the Himalayas, beyond wifi for a while. I'm a friend of Geoff's and an IB Chemistry workshop leader, helping out on the website while he's away. 2,4DNPH and Tollen's are not required to be taught. I think that students only need to know about suitable reducing agents (e.g. lithium aluminium hydride and sodium borohydride) and suitable oxidising agents (e.g. potassium dichromate) in relation to aldehydes and ketones. Best wishes

Bill Chia 22 February 2018 - 01:37

Thanks Paul!

SHALINI SHARMA 3 March 2018 - 04:42

Dear Geoffrey,
With our students ready for the final battle, all of us are as anxious as them.
A student asked this question, to which my answer is a 'tentative' no but I wish to clarify from you.
Can [H2O] be ignored while calculating Kc of esterification reaction? My co-teacher feels it can be if the acid and alcohols used are dilute. If yes, then how do we define the extent of dilution?
Can you please shed some light?
Warm regards,

Paul Lloyd 4 March 2018 - 16:31

Dear Shalini
Geoff is away in the Himalayas, beyond wifi for a while. I'm a friend of Geoff's and an IB Chemistry workshop leader, helping out on the website while he's away.
My feeling is that [H2O] cannot be ignored; it is included in the Kc expression, and so should be included in calculating Kc. However, if the organic acid and the alcohol are both in dilute aqueous solution then it may be that we could consider the [H2O] to effectively be a constant (like we do with Ka) in the expression; the 'concentration' of pure water is approx 55.5 mol dm-3. However, I wouldn't recommend to the students to ignore [H2O]; could get themselves into problems!
Hope that helps; Geoff is back in a couple of days, and I'll ask if he agrees!

SHALINI SHARMA 5 March 2018 - 08:42

Dear Paul,
Thanks a billion. That surely helps.

Geoffrey Neuss 8 March 2018 - 00:30

Hi Shalini, I do agree with Paul. Normally in IB questions on esterification it is assumed that pure acid and pure alcohol are used as the reagents and water is a product (not a solvent) and therefore must be included in the calculation.

Puja Goyal 11 April 2018 - 16:48

yes sir i was initially confused but then i realized that water is a product in the reaction and not a solvent so it cant be ignored and has to be included.

Xiaodan Wang 22 March 2018 - 05:34

Dear Geoffery,
Here is a question from IB online question bank.
Which conditions are used to convert ethanol to ethanal?
A. Excess oxidizing agent and reflux
B. Excess oxidizing agent and distillation
C. Excess ethanol and reflux
D. Excess ethanol and distillation
I think the correct answer is B but IB says the answer is D. What do you think? [The reference code of this question is]

Geoffrey Neuss 22 March 2018 - 09:38

Hi Xiaodan, In order to minimise further oxidation to ethanoic acid, the oxidising agent should be the limiting reagent and the ethanal should be removed from the reaction mixture by distillation as soon as it is formed. So to me D is the best answer.

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