InThinking Subject Sites
Subscription websites for IB teachers & their classes
Disclaimer: InThinking subject sites are neither endorsed by nor connected with the International Baccalaureate Organisation.
IB Approved Workshops
Chemistry (New Syllabus)
IB DP Category 2
Stockholm, Sweden, 3 - 5 May 2024
Find out more
Chemistry (New Syllabus)
IB DP Category 2
Berlin, Germany, 23 - 25 August 2024
Find out more
Find all InThinking Workshops at www.inthinking.net
Subscriber comments
- Thank you for the detailed explanation and for giving your time,
- hello Geoff. I just want to ask you. Do particles stop moving at absolute zero? Because we are having a dialogue with physics teachers about it. They are saying that particles sill have motion and kinetic energy.
- Hello Fulya,Ethanal (acetaldehyde) gives two signals (with an integration trace of 3:1) in its low-resolution 1H NMR spectrum as it contains protons in two different chemical environments. The splitting of these two signals will be shown in...
- Hi,I have a question about Question 6, I wonder how ethanal will have a doublet in its H NMR spectrum,Many thanks
- Hello Leonie, I think that delivering the new syllabus by placing the emphasis more on the underlying concepts is a great idea and compared to past syllabuses I think you will find that you have more time to do this as the content is definitely...
- Hello Charmaine,The problem with producing a list of chemical substances that are forbidden for use in schools is that different rules and regulations apply in different countries and often even within different regions of the same country....
- Thank you!
- Hi Geoff, Hope you are well. Thank you for sharing the resources. I am after a bit of advice. We are trying to deliver our new chemistry curriculum in a more conceptual approach and have designed a 'Fuels' unit which will...
- Hi Geoff, I'm curious if IB provides a list of prohibited chemicals for student use? I've read the whole guide, but found no mention of it. Of course, I prioritize safety and wouldn't permit any experiments posing explosion risks or potential...
- Hello Michelle, Maybe it might have been better if James had titled his video “These ideas for IAs are unlikely to score well”. The research question does not have to be over complicated, what matters is that it can address all the criteria....
- Maybe it is me, but I feel like the video "Not Awesome ideas for IA" seems overly harsh. We are an IB for All unscreened public HS and getting students to even replicate a simple kinetics experiment on their own is challenging as the first...
- Right Anthi.
- Hello, Enthalpy change of hydration and enthalpy change of solution are also absent in the new HL syllabus, right?
- Ana, You can give your students direct access to these practice papers simply by signing them up (for free) to Student Access.
- Hi Ana, See my answer to your other comment on the Grade Boundary page.
- Hi Ana, The simple answer is no as the boundaries are not determined until after the exams have been taken. In the past when there has been a change of syllabus the boundaries have not changed dramatically so using the past boundaries is probably...
- Hi Geoffrey,I saw your comment re he MC being available, but are these Practice paper 1 MC available to print?Thank you,Ana
- Hi,And grade boundaries for the new course?Thank you,Ana
- Hi,Do we have any idea re grade boundaries or just use previous years? Just planning for our end of year exams for current Year 12.Thank you !Ana
- Hello Tammie, I'm not sure why you want this as the IB operates on a 7-point scale and from the subject reports (which you can download from My IB) you can see what marks out of 24 for the IA correspond to the grades out of 7. I suspect the...
- Is there a conversion chart for converting the IA score to a traditional 10-point grading scale?
- Thank you Geoff. Yes nothing is stated on specimen papers or in the guide about reading time of Paper 1.
- Hi Leena,Look at the specimen papers for the 2023 programme (first exams May 2025) on My IB to see how they will be presented and marked.
- Paper 1 Section B Will it have both data based and experimental based questions?I there any weightage on them separately?
- Hello Renuka, As before there will be 5 minutes reading time for Paper 2. My understanding is that there will also be 5 minutes reading time for Paper 1 (this includes Section A and Section B) but, as far as I am aware, the IB has not announced...
- Dear Prof,Do we allow reading time 5 minutes to both Paper 1B and Paper 2 of the new curriculum? (First exam in May 2025)
- Thanks Mr. Geoffrey - I had this confusion because of the observation at the cathode - the appearance of Grey metal at cathode ( during Pb Br2)or pinkish metallic solid ( during CuCl2). So the metal ions...
- Hi Vinaya, I assume you mean the products of the electrolysis of molten sodium chloride? Sodium chloride melts at 801 oC. The melting point of sodium is 97.79 oC and the boiling point of sodium is 882.9 oC (see Section 8 of the 2023 IB data...
- Hello Mr.Geofrey, I have a confusion : The product of molten NaCl- will it be Na(s) or Na(l) ?
- Right! The question! That's what I missed :) I was actually looking at the answer only because of the example in the textbook, giving it other way around, so...anyway, it makes sense that gaseous state standard bond enthalpies should be used...
- Hi Demet, I guess it is all to do with answering the question. The question starts, "Use the bond enthalpies and average bond enthalpies...." rather than "Use the enthalpies of formation....". If you just use enthalpies of formation all you...
- Hi, Slide 14 Q2 ; why don't we use formation enthalpies of CO, O2 and CO2 for delta H1 and H2? Am I missing something?Thanks!
- Hello again Renuka,This IB multiple choice question on M2021HLP1TZ1 asks which solution has a pH of 9. Response A is 1.0 x 10-9 mol dm-3 HCl (aq) and response B to is 1.0 x 10-5 mol dm-3 KOH (aq). The pH of 1.0 x 10-9 mol dm-3 HCl (aq)...
- Dear Prof,May 20 21 Paper 1 TZ1 Question 25According to the making scheme answer is B and I am agree but why answer A is not correct?pH value in both answer A and B are the same and it is 9.Renuka
- Thank you so much.
- Oh! now I understand the problem. I extracted the question from the question bank but the question provided in the question bank is incomplete and section A and B are missing.
- Hello Renuka,You don't need the half-life of 228Ac to solve c(ii) although you do have it, as part (b) in the same question tells you that a sample of 228Ac decreases to 1/8 of its original value in about 18 hours and then asks you to estimate...
- The question 17N.3.hl.TZ0.18, tFrom the section Ci the mass loss for 0.00100 mol and energy produce were calculated as «E = mc2 = 1.86 x 10–9 kg x (3.00 x 108 m s–1)2 =» 1.67 x 108 «J»The section Cii, askedDetermine...
- Thank you so much for your valuable input. I will also go through the TSM.
- Hello Vinaya,I suggest you look at page 81 (and the pages around there) in the Teachers Support Material (downloadable from My IB) as that has quite a good section on what the IB expects and gives an example using the difference in two temperatures...
- Hello Mr. Geoffrey,I have a query regrading significant numbers/decimal places in burette reading. So the burette has +-0.05 uncertainty .If the initial reading is 10.00ml +- 0.05 and final reading...
- Hi Geoff,Thank you for your quick reply. Yes, indeed, this is for the new syllabus (first exams May 2025). Your feedback confirms my own feelings on the matter, but perhaps I will follow up with my coordinator or an IB forum to further confirm...
- Hello Pete, Your question might have been a bit easier to answer if your students were following the 2014 syllabus but as it is an EE I guess they are following the new 2023 syllabus for the first exams in May next year. There is now no biochemistry...
- Hi Geoff, I have some extended essay students. Their ideas are biochemistry in nature, and my concern is about which subject to put them into.For example: A student looking at lactic acid fermentation, and how the starting pH of the fermentation...
- Hi Demet, Just to add to what Paul has written. The enthalpies of formation are both exothermic, so although liquid water has the lowest negative value it gives out more heat during its formation. Less heat is given out when steam is formed...
- Hi DemetYes, extra heat energy is released as the water vapour condenses to liquid water (latent heat); energy that moves from the system to the surroundings as bonds, in this case hydrogen bonds, are formed. When you mention Hf values, I assume...
- Hello Paul,Thank you very much for the reply.Nitha
- Hi,Slide 11, Q3; answer says; burn from the steam is worse than boiling water. It's because steam condenses to water when hits the skin therefore more energy released. Correct? A student mentioned that if one focuses on the Hf values it might...
- Hello, NithaGeoff is in the wilds of Pembrokeshire at the moment. As I understand it, for the new course, both papers 1 and 2 will have 5 minutes of reading time when they are first examined in 2025.Paul
- Hello Mr. NeussIs there possibly a 5-minute reading time allowed for both papers or only for Paper 2 like in the old syllabus? I seem not to have found any information on this in the guide or PRC. Thank you.
- Hi Boopathy, 1 mole of MS2 would contain 64.0 g of S. 26.0 g of MS2 contains 16.0 g of S and 10.0 g of M so mass of M combining with 64.0 g of S = 4 x 10.0 = 40.0 g so relative atomic mass of M = 40.0.
- How to solve this questionMetal M reacts with 16.0g of sulfur to produce 26.0g of the compound MS2. What is the relative atomic mass of M?
- Hi Geoffrey, thank you for the prompt reply. It was just the pandemic year when all IAs were marked externally that was the exception. Your work with this Thinkib website is excellent, thank you for sharing all your experience and knowledge...
- OK, the Penny Dropped for me at last. thank you Geoff for thinking up such a stimulating question!!
- I should say that I'm comparing experiments 1 and 3, where nothing is changing apart from the Iodine concentration which is being halved, and the rate, which appears to double...
- agreed Geoff, but the rate is changing in the question; the rate is actually doubling, as the time taken is halved...just not what I was expecting if it were zero order...I must be having a Senior Moment today... :(
- It is a good point Adrian but it is more a question of the use of language than precise terminology, i.e. what the IB uses at this level. In the guide (R3.3.1) it identifies radicals with a dot. The dot represents an unpaired electron. Oxygen...
- Hi Ian, I am absolutely sure. the rate does not change when the concentration of iodine is halved. You need to consider what rate you are actually measuring. When the amount of iodine present is halved the time for the iodine to disappear is...
- Hi Geoff, Thank you for the useful set of slides. One of my students brought up the problem of representing oxygen atoms as radicals. Many sources present them as such when in fact they have an even pair of electrons which suggests we...
- Are you sure 16 can be solved? the rate seems to double while the iodine concentration is halved... :) the logic in the answers doesn't make sense to me either! If the concentration changes, and the rate changes in some way, surely the...
- HI Douglas,The answer to your question is stated clearly in the Teacher's Support Material published by the IB on page 88. "It is strongly recommended that comments are made on the work". It goes on to explain that this helps examiners understand...
- Hello, do you advise we submit annotated copies of the student's IA when called for external moderation, or just submit a clean draft along with the document that has the table for each criterion and the justification comment? I understand...
- Hello Kate,"Define" is not listed by the IB as a command term, as the IB places more emphasis on understanding the underlying principles. The lattice enthalpy of sodium chloride is 790 kJ mol−1. This can be defined either as the energy given...
- Hello GeoffIs there any chance of commenting on the below before Friday 10th please - I would like to set questions as test Monday 11th - Many thanks, R1 First test number 13 and R1 Second test number 13 Has lattice enthalpy definition...
- Hello Mona,Since it refers to the enthalpy diagram it means they are more thermodynamically stable (not necessarily more kinetically stable), i.e. the bonds in the products are stronger than the bonds in the reactants. This is the case for...
- Hello Geoff, In reference to slide 3, when we say that products are more stable than reactants in exothermic reactions, what do we mean here by stability - what is it reflecting? And how do we relate it to the bond enthalpies in the substances...
- thank you Mr.Geoffrey
- Thank you for your prompt reply Geoffrey,Yes, I am asking mainly in regards to aligning the marking of our own internal unit tests and mock exams to the marking of the actual exams. I understand that you cannot give an official IB answer,...
- Hello Vinaya, 1. Students will not be penalised if they use ml in their EE or IA but it is much better to train them to use cm3 as that is the unit that will be used in examination questions.2. It depends. It is not a bad generalisation...
- Hello Mr. Geoffrey,I have three questions: 1) I have one confusion regarding cm3 and mL. Is it ok to use mL instead of cm3 in IA/EE ? 2) In Chemistry , we usually tell students to keep to 3 significant numbers in the calculations....
- Hello Seth,Even though I've got many years of experience setting external IB chemistry papers (and their markschemes) and acting as the principal examiner for both Papers 2 and 3 (Paper 1 is marked electronically) please remember that my answer...
- Hello, I don't know if anyone at InThinking or any reading this who have moderated exams could help with the following, or where I might go to obtain an answer to two general questions I had about marking short answer questions 1) If the...
- Hello Geoffrey, It's very kind of you to have sent me this example and the ressources, thank you ! I purposefully did not mention Nernst equation, I understand that it's more about the concentrations (but it is validating to see it...
- Thanks Geoff, yes, you're correct... this came from the Hess's Law experiment. I guess my issue therefore comes from definitions. Thanks for your detailed explanation; the inclusion of enthalpy of solution will be helpful when discussing...
- An interesting question Gareth! I guess to some extent it depends upon how neutralisation is defined. Some definitions only effectively cover the reaction between H+(aq) and OH−(aq) to form water so they will always be exothermic. Other...
- Hi Geoff,Are all neutralisation reactions actually exothermic? For example, I would consider the reaction between potassium hydrogencarbonate and hydrochloric acid to be a neutralisation reaction, yet this is an endothermic reaction. I...
- Hello John,I hope I am understanding your point correctly. The lines converge towards the high energy end of the spectrum. The first line in the visible region (where electrons drop down to the n =2 level) must be the line with the lowest...
- Hello Geoffrey,S1.3 Electron configuration the question states - " ....give the third line in the visible series" The answer key states that this is the 5-2 transition. I have always thought this was clear, but I had...
- Hi Jenny,Students often do try to investigate the relationship between temperature and cell potential but with varying degrees of success. However, the relationship is not simple as it depends upon several different factors. You have not...
- Good evening Geoffrey, One of my student decided to explore the effect of temperature on a Zn/Cu cell voltage. He was using 1 M concentrations and just warming up the electrolytes (in 5 K increments from room temp to 318 K) before taking...
- Hello Mia and Geoff. Having a well-trained and proactive lab technitian is very necessary.
- Dear Dr Neuss,Splendid!! Thanks for the swift response and update. Cheers :).
- Hello Yussuf, Many thanks for your kind comments. You are quite correct, it should be sodium hydroxide, not methanoic acid - thank you for pointing it out. I have corrected it now.
- Dear Dr Neuss,Firstly, thanks for the comprehensive resources :).In the response to Question 3 of the task, it was mentioned that 10cm3 of the 0.120 M methanoic must be added. I'll just like to clarify if this is an error, and if yes should...
- Thank you. I appreciate your perspective. I definitely will go over the basics of the concept but I think, due to time, I will omit a huge inquiry lab I normally did on the topic so I can focus more on some other calorimetry labs....
- Hi Angie, Enthalpy of solution has disappeared from the syllabus and the 2023 data booklet no longer contains the sections on Enthalpies of aqueous solutions and Enthalpies of hydration (Sections 19 and 20 in the 2016 data booklet). I do still...
- I have not seen anything in the guide regarding enthalpy of solution and I don't see anything in your notes. Is this something that no longer should be taught for the 2025 assessment? I am nervous to leave out of the curriculum...
- Hi again Harprit, Try using the van Arkel-Ketelaar diagram to determine whether or not BF3, CCl4 and CO2 are polar. You will not get very far, as the diagram is for determining the type of bonding within a substance. It does not take...
- Syed, Students need to choose the best answer. Students should be able to convert between molar amounts and mass. There is no reason why responses with different units cannot be given. In fact, this question reinforces the importance of units....
- I think I failed to explain my concern. There concentration of both solutions is given in mol/dm3. But answer is in g/dm3. Which is misleading as one of the option is close to the concentration mol/dm3.
- Thanks Geoff. Maybe, I'm trying to impose too much order on the IB guide but... I traditionally say to students that we deem the polarity of the C-H bond to be so low that we essentially treat at it as being non-polar. There's nothing explicit...
- thanks for the quick response. I know the kinetics of that reaction well so couldn't work out why so many of my students were giving the wrong answer
- Thanks a lot Geoffrey
- Hello Harprit, Since they are not specifically mentioned in the syllabus, the IB should not require students to state whether they are polar or not. However, a good question might be to ask students to discuss how the shape of the molecule...
- Hi Soumitri, If each reading on the burette you are using has an uncertainty of 0.05 cm3, then if the initial reading is 0.00 cm3 and the final reading is 45.00 cm3, the measured volume lies between 44.90 cm3 and 45.10 cm3 so giving the final...
- Hi Geoff. I have a question about molecular polarity. Things like PH3 and NCl3 have electronegtaivity differences that are small and generally considered non polar. The pyramidal shape though does give an overall dipole and these molecules...
- Hi Geoffrey, I have a doubt in error propagation. For burette, uncertainty is + or - 0.05cm3 for each reading right, initial volume is 0.00cm3, and final volume is 45.00cm3, so for the final titer value uncertainty should...
- Hi Syed, No, there is no mistake. Concentrations can be expressed in mol dm−3 or in g dm−3. In S1.4.3 it states, "Students should be able to solve problems involving the relationships between the number of particles, the amount of substance...
- Hi Angelique, No there is no mistake. The rate is being followed by measuring the time taken for the colour of the iodine to disappear. If you only put half as much iodine in a fixed volume of the mixture without altering the overall volume...
- Hi Dea, Thank you for reporting this. You are quite right. It should be − 147 (kJ), not + 147 (kJ). I've corrected it now.
- Hi Geof: In question 2, you ask for the resultant concentration after mixing two solutions but the answer is in g/dm3. To me, it is misleading as both concentrations are mol/dm3. Could you please clarify if there is a mistake or if I misunderstood...
- Is there a mistake in question 16. should propanone's conc be 0.8 for reaction 3?
- R.1 Firsty test number 18: The hess law is correctly used but the math after that is incorrect. My calculation shows the answer is in negative sign.
- Minor point - University of Toronto not Toronto University.
- Hello Mara,In the past, I did not usually include the answers to the questions on the practicals as many of them depend upon the data collected by the student so will be different for different students and I also assumed teachers would be...