Syntactic and Syndiotactic are NOT Synonymous

 

Question 20 from paper 1 of the QCAA chemistry exam 2022 is shown below. Can you answer it?

 

 You can if you make a couple of assumptions first:

1/ The 3D structure isn't given, so you have to assume (given the possible answers) that methyl groups above the chain are in fact coming out of the plane, while methyl groups below the chain are behind the plane.

2/ You have to assume that "syntactic" is a misprint of "syndiotactic" since there was no mention of this being a composite material.

Then you can choose (A) as the answer, and according to the answer sheet you would be correct.

 

However, here is an excerpt from the draft new Queensland Chemistry syllabus (for implementation in 2025 I believe),

      "Describe the structure features of

           -polyethene (LDPE and HDPE), polypropene (syntactic, isotactic and atactic) and                                             polytetrafluorethene."

(Cross my heart, this is what is says, the syllabus writers seem to have difficulties with adjectives as well as chemical nomenclature, where are the round brackets around tetrafluoroethene?)

 

So, it appears that students will study tacticity of polymers but only isotactic and atactic not syndiotactic, then they will look at composite materials in the form of syntactic foams.

Really?

 

Dear Queensland Chemistry syllabus and exam writers, the 3D structure of a polymer results in an isotactic, syndiotactic or atactic polymer.

A syntactic foam refers to a composite material in which hollow spheres are bound together by a polymer.

Making it harder to cheat

Here is the problem: teachers want to engage their students with interesting demonstrations and activities to motivate them to think about  a scientific concept. Students, on the other hand, just need a good mark on the tests and assignments so they can become a doctor, or a lawyer, a cobbler or a candlestick maker, etc.

As the technology available to students to help them answer their assignment questions gets better, teachers need to think about how to structure questions to make students think, rather than just google the answer.

Here is an example of a pretty standard sort of test/assignment question; What properties of aluminium make it suitable for use in cooking pots.  Give a disadvantage of using aluminium for pots.

If you copy and paste that into google, there are 2,090,000 results, and the top of the page will read, "Aluminum is lightweight, cheap and very good at distributing heat. It doesn't retain heat particularly well though, so the temperature will fluctuate as food is added to a hot pan. It's also the softest metal on our list, so it will scratch and dent pretty easily."

Assignment done! No thought required!

So we need to re-structure the question. How about this...

On the planet P42da, the element potsnpanium is used to make large pots in which the P42daians heat soup to above the boiling point of liquid water at 1 atmosphere. What properties of potsnpanium make it suitable for this purpose. Give an example of a safety precaution the P42daians should take when handling potsnpanium pots. Describe a way to reduce this hazard.

Copied and pasted into google this yields 0 results and a heap of useful suggestions:

"

• Make sure that all words are spelled correctly.
• Try different keywords.
• Try more general keywords.
• Try fewer keywords.

"

Might force some students to have a think about it.

How to study for Chemistry exams

As your chemistry exam gets closer, I'm sure you've been "studying" hard, probably reading through your notes, making summaries, summarizing the summaries, putting important concepts on flash cards... and a whole lot more. But will any of that help you achieve a good result on a chemistry exam?

Probably not. So, put your notes away and read on.

Chemistry examiners are not interested in whether you have memorized the "facts" (definitions, formulae etc). It is most unlikely that the following question will appear on a chemistry exam paper,

Question 1: "State Le Chatelier's Principle"

Chemistry examiners are interested in how you apply chemical principles to solve problems. So the following question is much more likely to be found on a chemistry exam paper,

Question 2: "A student dissolves some solid FeSCN²⁺ in water in a test tube at room temperature and pressure, producing a mixture of reddish-brown FeSCN²⁺(aq), pale yellow Fe³⁺(aq), and colourless SCN^-(aq). The student observes that the test tube feels cooler as the solute dissolves.

(a) Write an equation to describe the process.

(b) Describe what colour change, if any, would occur if the test tube was placed in an ice-bath. Explain your answer"

Question 2 is asking you to apply Le Chatelier's Principle to a given chemical process.

The best way to study for your chemistry exam is to answer a variety of questions. AUS-e-TUTE Members have access to thousands of problems (with worked solutions and tutorials if you need some help). If you are not an AUS-e-TUTE member you can often find books of problems for a given course, and you probably have access to "past papers". 

Here's another question you might like to try,

Question 3: One step in the Ostwald process for manufacturing nitric acid from ammonia involves the production of nitrogen dioxide as shown in the chemical equation below:

2NO(g) + O₂(g) ⇋ 2NO₂(g)

A 10.00 L reaction vessel initially contained 2.50 mol NO(g) and 1.20 mol O₂(g).

0.50 mol NO(g) remained in the vessel after equilibrium was established.

(a) Calculate the equilibrium constant for this reaction.

(b) A second experiment was conducted using the same initial amounts of NO(g) and O₂(g) but in a reaction vessel of about half the volume. What affect would this have on the value of the equilibrium constant? Explain your answer. 

If you find these questions a bit tricky, then AUS-e-TUTE might help you become more familiar with exam-type questions and how to answer them. Join AUS-e-TUTE today

How to Maximise Marks in Your Chemistry Exam

Are you ready for your chemistry exam?
The Sydney Morning Herald provided 8 dot points to help you answer Chemistry exam questions, which we have expanded out below:

• Write correctly balanced equations.(Include state, or phase, of matter)
• Structure your answers to ensure they are logical. Written calculations should be neatly organised and sequential.
  • If you dilute an acid with water at 25°C, the pH of the solution will not rise above 7
  • If you dilute a base with water at 25°C, the pH of the solution will not fall below 7
• Clearly label your graphs (plots, scale, axis, line of best fit).
• Use relevant scientific terminology.
  • Check your spelling! Ethane is NOT the same as ethene! Molarity is NOT the same as morality! Calorimetry is NOT the same as colorimetry!
  • If the question is about physical properties, think about intermolecular forces.
  • If the question is about chemical properties, think about intramolecular forces, and think about types of chemical reactions for inorganic chemicals and for organic chemicals (combustion, addition, substitution, elimination, condensation, polymerisation)
• Explain the underlying chemistry and provide relevant chemical equations.
  • Is it a gas question? Ideal Gas Law? Molar Volume? 
  • Precipitation question? Solubility Rules? Solubility Product? Gravimetric Analysis? Conductometric Analysis?  Argentimetric Analysis?
  • Equilibrium question? Equilibrium concepts? Le Chatelier's Principle? Equilibrium law?
  • Acid/base question? Definitions? Properties? Acid strength? Acid-dissociation constant? Neutralisation reaction? Titration techniques? Titration calculations?
  • Chemical kinetics question? Reaction rate? Maxwell-Boltzmann distribution?
  • Determination of organic structure? C-13 NMR, Mass Spectroscopy? IR Sopectroscopy?
• Use subscripts and superscripts where appropriate.
  • Formula of ions, superscript to right of symbol (number first followed by sign)
  • Formula of isotopes, mass number superscript to left of symbol, atomic number subscript to left of symbol 
  • Molecular formula or empirical formula, number of atoms of each element shown as a subscript to the right of the element's symbol
  • "States" or "phases" of matter are sometimes written as a subscript to the right of a molecular formula, eg, CO_2(g), but are usually written in line with with formula, eg, CO₂(g)
• Use stimulus materials to answer the question.
• Use clear labels when continuing responses in a different booklet.

ALWAYS check that you have answered the question that was asked, and not provided an answer to a question that you wish had been on the paper!

IUPAC Nomenclature and Organic Compounds

Imagine you are sitting a Chemistry exam.
The first question on the exam paper reads,

"Name the molecule shown below:"

How would you answer this question?

My first response is to name it Molly, short for molecule ofcourse. Not a very useful name, especially if I'm asked to name another molecule later on. It might get a bit confusing if I name every molecule Molly, even when the molecules are very different from each other.

So, the International Union of Pure and Applied Chemistry (IUPAC) has developed systems for naming compounds.
For this reason, you probably won't be asked to "name" the molecule, but you might be asked to "systematically name" the molecule, or to give the "systematic IUPAC name" for the molecule.

Even for the relatively simple molecule shown above, there is more than one way to systematically name the molecule using IUPAC nomenclature rules!

You could give a systematic IUPAC name based on the functional class of the compound. This molecule belongs to the functional class known as ketones (non-terminal C=O), two methyl (CH₃) groups are attached to the carbonyl carbon atom, so, according to the IUPAC rules for functional class nomenclature, I could systematically name it as dimethyl ketone.

I could give the same molecule a different systematic IUPAC name by applying the rules of substitutive nomenclature. In this case I name the parent hydride, propane, drop the final "e" and add a suffix denoting the non-terminal C=O functional group so that I get propanone, then I add in an infix which locates the functional group along the carbon chain, with the final name propan-2-one.

Because this is a simple molecule with just one functional group, I could use the infix as a prefix, so that the systematic IUPAC name would become 2-propanone. Or, because there is only one position for the C=O functional group to be in if this molecule is to be a ketone, I could drop the infix altogether and just systematically name the molecule as propanone.

So, some of the possible systematic IUPAC names for this molecule are:

• dimethyl ketone
• propan-2-one
• 2-propanone
• propanone

Because molecules can be named systematically in more than one way, there is a recommendation to adopt "preferred IUPAC names", or PINs. Usually the Preferred IUPAC Name is arrived at by using one of the recognized IUPAC systems for nomenclature, but not always.

If you were asked to give the Preferred IUPAC Name for the molecule shown above, the correct answer would be acetone ("Preferred names in the nomenclature of organic compounds" (Draft 7 October 2004) page 9), or, possibly propan-2-one ("Preferred names in the nomenclature of organic compounds" (Draft 7 October 2004) page 374). Acetone is the traditional name for this compound, literally meaning 'derived from acetic acid', and has been in use for more than 200 years, which is probably why the IUPAC would consider retaining the name "acetone" as the Preferred IUPAC Name for this compound.

Further Reading:
Introduction to Naming Organic Compounds

60 Second Chemistry Quiz Challenge

Over the past few years AUS-e-TUTE has received a lot of feedback.
One of the things that we hear a lot from teachers who are part of an AUS-e-TUTE Class or School Group Membership is that the students love to do the drills. They love to see how many questions they can get done quickly.
Well ..... we thought we could turn some basic chemistry concepts into timed challenges.
And ..... we've just uploaded the very first of these. We've called it the 60 Second Chemistry Quiz Challenge because you have just 60 seconds to answer as many questions correctly as you can.
This 60 Second Chemistry Quiz Challenge is called "It's Elementary", so I'm sure you can already guess what the questions are about :)

You can have a go yourself at:
http://www.ausetute.com.au/challenge.html

and let us know what you think by emailing us at

Spelling Mistakes vs Incorrect Science

It's that time of year in Australia when tens of thousands of students get ready to sit their final exams.
For many of these students it will be the first time they have sat an external assessment, that is, these exams will not be marked by teachers who know them. This time there will be no kindly teacher marking the exam paper and thinking, "oh dear, well I know what Chris really meant ....", this time a complete stranger will be sitting in front of your paper, and not only that, a complete stranger who has by now had to try to read and mark thousands of papers, and this stranger is only going to give you a mark based on exactly what you did write NOT on what he/she thinks you might have meant!

Which brings me to the subject of this discussion. 
When is a spelling mistake (typo) going to be marked as wrong on a Chemistry exam paper?
A spelling mistake will be marked wrong if it introduces ambiguity into your answer or if it makes what you are saying scientifically incorrect.

Spelling mistakes that will be probably not be marked as wrong include misplaced apostrophes, for example it's instead of its, or misspelling non-science-specific-words like using 'their' instead of 'there', as long as this does not alter the scientific meaning of what you have written.

Spelling mistakes that will definitely be marked wrong are those that make your answer scientifically "wrong".
In chemistry, changing just one letter in a word can have an enormous impact!
For example, ethane has the molecular formula C₂H₆ and is a saturated, and not very reactive, hydrocarbon. On the other hand, ethyne has the molecular formula C₂H₂ and is an unsaturated, and very reactive, hydrocarbon. Changing one letter, an a to a y, has a huge impact on the formula and properties of the compound! If you start writing about the addition of bromine to ethane instead of ethyne you will, and certainly should be, marked wrong.
Then there is the problem of capitalization, which is very important when writing chemical formula.
If you write Co then you have given the chemical symbol for the transition metal cobalt, but if you write CO you have given the molecular formula for the covalent compound carbon monoxide. Just using a lowercase letter instead of a capital (uppercase) letter  has changed the substance from a metallic element to a covalent compound! So, if you start talking about the metallic bonding of CO in the solid state at room temperature and pressure, you will be marked wrong.

After you have written an answer to an exam question, read the question again. Then read your answer. Make sure you have written an answer to the question that was asked, and, make sure that your answer says what you meant it to say! Be on the look-out for those spelling mistakes (typos) that could lose you marks.

Exam Technique 1

I've never written a blog post about exam technique before, but after reading the following question on an exam paper, I felt the time had come to broach the subject.

Imagine being a High School Chemistry student who is confronted by the following scenario on an exam paper:

• Written information that tells you that the diagram refers to an experiment to model a process and observe the colour change of crystals.
  
• A diagram of a dessicator (labelled as a sealed container) containing a watch glass of copper(II) sulphate pentahydrate (no indication of colour) and a beaker labelled Liquid X.
• And the instruction that the student must identify Liquid X and explain the colour change of the crystals.

So, where do you start, given that you have so very little information to go on?

You might start with the dessicator (assuming you have recognized it as a dessicator and that you know what it is used for). This would suggest that, whatever this 'process' is, it is effected by water.

That copper(II) sulphate pentahydrate could also be a clue. It is copper(II) sulfate that is hydrated, CuSO₄.5H₂O, so if you are taking the trouble to keep moisture out of the dessicator, then maybe Liquid X in the beaker is a dessicant, something that will remove water from the air, and hence from the copper(II) sulphate pentahydrate.

Now, you would need to know, or infer from the question, that there is a colour change involved. Copper(II) sulphate pentahydrate is actually blue, while anhydrous copper(II) sulphate is off-white in colour.

But you still haven't answered the first part of the question, you must identify Liquid X. And this is where it becomes very, very, difficult. If you are sensible at this point, you might just call Liquid X a dessicant, and hope the exam markers will accept that. Otherwise you are going to come up against the nasty problem of naming a dessicant that is a liquid (not a solution, not a gel, but a liquid). So, is there such a dessicant?

Silica gel is a commonly used dessicant, but it is not a liquid, it is a very solid-like gel.

Lots of solids are commonly used as dessicants, including activated carbon, calcium sulphate, calcium chloride, and swelling-clay minerals like bentonite. You can even use sodium hydroxide as a dessicant.

Strangely enough, the term "liquid dessicant" is used in the air-conditioning industry, but the dessicant is not a liquid, it is usually solid lithium chloride.

Well, I haven't had any luck coming up with the name of a liquid dessicant.

Clearly, we have started off in the wrong direction. The resemblance of the vessel to a dessicator is probably a red-herring, something put into the question in order to get you to think along the wrong lines. Is the use of hydrated copper(II) sulphate also a red-herring?

Well, I'll keep working on the problem, but, if I was a student trying to complete the exam within the time-limit, I would have realized that this question was only worth 3 marks, and I couldn't afford to spend more than about 5 minutes on it....

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