Preparing for IB Chemistry Paper 3

Written by Chris; Chris is available for private tutoring.

In this post we are going to look at Paper 3 in IB chemistry and some good ways to prepare yourself for sitting it. I will mainly be focusing on Section A of the paper but will talk you through a few things you can do regarding the Option.

How important is Paper 3?

One of the first things is to be aware that depending on whether you are doing SL or HL, Paper 3 is worth a different amount of your total mark.

Standard LevelHigher Level
Paper 3 as % of overall mark2024
Paper 2 as % of overall mark4036
Ratio Paper 3-to-Paper 21:22:3
Paper 3 marks on Option20 out of 35 (57%)30 out of 45 (67%)
Marks on Option as % of overall11.416.0
Hours teaching on Option15 out of 110 (13.6%)25 out of 180 (13.9%)

The 1:2 ratio of marks (paper 3-to-paper 2) for SL versus the 2:3 ratio for HL is important to bear in mind when deciding how much time to give over to each exam in preparation.

On a similar note, the emphasis on the Option is different for SL and HL. The Option forms a much smaller fraction of the overall mark if you are studying it at SL. It is also worth noting that the Option takes about the same amount of recommended teaching time in both SL and HL (about 13.5-14%). However, for HL students, the Option is significantly more important and so preparation should be very thorough.

Paper 3 – The Breakdown

Paper 3 comprises two sections; Section A is compulsory and you will most likely have two questions of which one will be data-based and the second will be based on at least one of the prescribed practicals you should have carried out during your taught course. Irrespective of level, this section is worth 15 marks of the total for paper 3; it is therefore more significant for SL students. Section B contains questions on each of the four available Options: Materials, Biochemistry, Energy and Medicinal Chemistry. You must choose a single Option and answer all the questions on it.

Do not fall for the false belief that Paper 3 is “The Option Paper” as many students do. Yes, it forms the major part of the paper but the questions in Section A are equally important. The danger of this belief as a student is that you spend too long preparing for the Option and, perhaps, only the Option before sitting the paper whilst neglecting preparation for Section A. Additionally, in my professional capacity I have seen a worrying number of students completely miss out Section A and go straight to the Option. Fortunately, this has mainly happened during mock exam periods when the consequences are minimal but don’t make the same mistake.

Preparing for Section A – Practical Work

This is where I want to focus as, in my experience, this is the single most challenging series of questions for students across all three Chemistry papers. The reason this section appears as difficult as it does is, principally, due to the lack of focus on the types of questions it contains during the teaching of the course coupled with the general attitude of students towards practical work and its importance.

Whilst you may not have any influence on how often you are exposed to Section A-type questions, you can certainly make a big difference in the way you approach practical work and what information and understanding you can gain from it. My advice is:

“TAKE PRACTICAL WORK SERIOUSLY AND MAKE NOTES”

The IB has ten prescribed practicals that all IB students must complete as part of the course. These practicals are given as:

Topic 1.2 Obtaining and using experimental data for deriving empirical formulas from reactions involving mass changes.
Topic 1.3 Use of the experimental method of titration to calculate the concentration of a solution by reference to a standard solution.
Topic 1.3 Obtaining and using experimental values to calculate the molar mass of a gas from the ideal gas equation.
Topic 5.1 A calorimetry experiment for an enthalpy of reaction should be covered and the results evaluated.
Topic 6.1 Investigation of rates of reaction experimentally and evaluation of results.
Topic 8.2 Candidates should have experience of acid–base titrations with different indicators.
Topic 8.3 Students should be familiar with the use of a pH meter and universal indicator.
Topic 9.2 Performance of laboratory experiments involving a typical voltaic cell using two metal/metal–ion half-cells.
Topic 10.1 Construction of 3D models (real or virtual) of organic molecules.
Topic 19.1 Perform lab experiments which could include single replacement reactions in aqueous solutions.

These entries are suitably vague to allow schools some freedom of choice when it comes to designing even the compulsory sections of their practical schemes of work. However, these ten items form the basis for questions in Section A and so it is crucial that you are aware of what practical work might be examined as well as when to take extra notes in class.

Based on information in the table, there are some fairly obvious experiments that might end up on your exam. Clear favourites would include:

  • Making a standard solution using volumetric glassware
  • Performing a simple titration, e.g., between HCl and NaOH
  • Determining the Mr of butane using a gas canister
  • Determining the empirical formula of an oxide of magnesium
  • Clock reactions, e.g., the iodine clock
  • Effects on the rates of:
    • decomposition of hydrogen peroxide
    • reaction between HCl and Na2S2O3
    • reaction between HCl and CaCO3 or Mg ribbon
  • Determining the enthalpy change of:
    • combustion of a fuel
    • solution of a salt
    • a single displacement reaction such as Zn + CuSO4
  • Making a voltaic cell.

This list is far from exhaustive; you may have done some of these experiments yourself or have done something similar. The key thing is to recognise that the focus on these experiments in Paper 3 is not going to be on the calculations but more on the methodology adopted. This is the bit students don’t pay enough attention to during practical lessons.

A few ideas of things to think about when doing these prescribed practicals are:

  • Why am I using these particular pieces of apparatus or chemicals?
    • Can I explain why a volumetric flask is crucial for making precise concentrations of solutions?
    • Can I explain why my calorimeter is made of this particular material?
    • Why can I not use sulfuric acid in the reaction between and acid and calcium carbonate?
  • What difference would it make if I used different pieces of apparatus?
    • What is the difference between using a pipette, burette, measuring cylinder or beaker to measure out a volume of solution?
    • How could I make my data more precise?
  • Is the order and manner in which the steps are carried out important?
    • Why is this particular reactant in excess? What might happen if I changed the limiting reactant?
  • What are the main sources of random and systematic error?
    • Random errors are unavoidable and present every time you take a measurement.
    • Systematic errors are caused by method failures and can be eliminated.
  • What assumptions, approximations or errors have I made in my data processing?
    • Is the density and specific heat capacity of my solution the same as those for water?
    • Have I converted my data into the correct units for the calculation?

As you can imagine, there are simply hundreds of possible things to think about when doing a practical, but the main thing is that you make some effort to do so. Don’t just follow the instructions blindly or ignore them and do your own thing. Think about “why you are doing what you are doing”.

Looking back over the small number of available past papers (link provided at bottom of page) the IB has examined:

  • acid-base titration and preparation of a standard solution
  • Determining the moles of water of crystallisation in a hydrated salt.
  • Determining the Mr of butane using a gas cylinder.

Familiarising yourself with these questions and the sorts of thing that we asked is an essential part of any preparation and can give you some idea of what to focus on during practical classes.

Preparing for Paper 3 – Data-based Questions

This is, arguably, the hardest part of the three exams to prepare for as the examiners could pick data related to literally any part of the taught course. Since exam questions for the new syllabus first appeared in May 2016, the IB has mainly used environmental or atmospheric chemistry contexts. These aspects of Chemistry are only briefly mentioned in the specification but are perfect for data-based questions. You should expect to have to interpret one or more sets of graphical and/or tabulated data. Questions may involve describing, explaining or calculating based on the data provided.

Again, although the IB has used mainly environmental chemistry as a context, do not anticipate this. You could easily be given data on bond angles, enthalpy changes, polarity, pKa and pKb, electrode potentials, etc. However, remember that the subject matter will be something you are likely to have revised for already and, with luck, some of the questions will require descriptions or calculations.

There are some simple guidelines to follow when trying to interpret unfamiliar data:

  • Read absolutely everything in the question, including any rubric or small print.
  • Take careful note of the column headings, units used, axis labels, etc.
  • Is there a trend within the data? Don’t think that all data presented must have a clear trend. Sometimes there is no obviously link between variables. Don’t be afraid to say this if the data don’t support a strong correlation.
  • Look for the obvious. Don’t try to do complicated or detailed analysis right away.
  • Read all the questions before doing any analysis. This will help you to focus on what is required and which data are superfluous.

Do make sure you know the difference between the command terms used by IB examiners in the questions. Are you sure you know the difference between: describe, explain, outline, summarise, deduce, etc.? I often find myself marking students down for not answering the question posed but a slightly different one, e.g., they describe a trend rather than explain it.

Preparing for Paper 3 – The Option

I am only going to give some brief advice here; we have already looked at the relative weighting of the Option in both HL and SL courses. Depending on the school you are enrolled in and the resources it has available you may find yourself well supported or on your own when it comes to the Option. If you fall into the latter category then make sure you collect as many resources as possible to help you. I would advise obtaining some published materials rather than only those provided by your school (links provided at bottom of page). The Options are varied and contain multiple subtopics and it is unlikely that any single teacher is an expert in all of them.

If you have any say in which Option you study you might want to consider these thoughts. I have taught and written about the Options many times in the past few years and my honest belief is that the Medicinal Chemistry option is the simplest and most sensible to study unless you have a clear strength in Physics or interest in another topic. The Medicinal Chemistry option contains many aspects that are simply slight extensions to the core material you will have covered elsewhere in your course. In the other topics you will find yourself learning completely new material without prior basis.

That said, if you are studying IB Physics you may wish to choose the Energy option as there is some overlap. Similarly, if you take IB Biology, then the Biochemistry option contains some material you will be familiar with already.

I would urge you to think very carefully before studying the Materials option. This looks to be the most challenging Option based on both content and difficulty of exam question.

One problem you may face when it comes to preparation for the Option, is a lack of practice questions. However, there is still quite a lot of similar content between the new syllabus and the old one. This means that some questions from older past papers (link provided at bottom of page) are just as relevant to the course you are taking. Options A and C (Materials and Energy) share content with the previous Options of Chemistry in Industry and Technology and Environmental Chemistry, Option B (Human Biochemistry) unsurprisingly has shared content with the old Biochemistry option and Option D (Medicinal Chemistry) has shared content with the old Medicines and Drugs option. If you are careful, you can select (or ask a teacher to help you select) those questions relevant to the current syllabus from papers going back over a decade.

Available Past Papers can be found here: Past Papers

Be sure to give us a shout if you have any questions!

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