9.4.4 HSC Question Feedback

This set of questions was a perfect example of why it is so important to be thorough with your Chemistry. Most people for most extended response questions lost a mark for a small error or because thye didn’t use an important Chemistry term in their answer. As a one off it does not really matter but across the whole paper it counts for approximately 25% of the available marks.

But generally the answers were very good and you should feel proud that you have completed so many HSC questions this early in the course. There are many students who wont even start doing this sort of work until stuvac. We have a whole 6 months to clarify any misconceptions, reinforce the depth of out understanding and fine-tune our exam technique.

 Specific feeback

2001

Q27) This was a tricky question to navigate because the source was unusual. It was a diagamatic graph. But because it was a graph it contained data and that measn you need to specifically refer to it. Eg “Ozone is mostly found in the stratosphere (up to 4.7ppm), while it is a maximum of 0.9ppm in the troposphere”. You then needed to describe its effects ‘nearby’ and ‘ip high’, which we did well BUT you need to sue the correct terms. Don’t call it the lower atmosphere  - call it the troposphere. Don’t say the ozone is in the upper atmosphere – say the stratosphere.

2002

Q25) b) This should have been an easy two marks but you need to be able to draw Lewis dot diagrams correctly (dots or lines – NOT both lines and dots for the bonds). You should always label the coordinate covalent bond.

Q25) c) Remember the dot next to the free radical. Also a phrase you need to work into ALL of your answers about CFC’s impacting ozone is “Cl free radicals catalyse ozone decomposition”.

2003

Q12) Because the graph showed the breakdown of one mole, you could just read off the graph C:F:Cl = 2:4:2 and remember wee don’t simplify covalent compounds (only ionic).

2004

Q12) We will cover this in the Acidic Environment topic

Q27) Answered really well but you need to refer to the data in the table. You need to describe CFC’s impacts (another opportunity to write: “Cl free radicals catalyse ozone decomposition”), refer to HCFC and HFC’s. You need to say the + and – of each and assess. which is most suitable. Also – 7 marks is a LOT – you MUST use chemical equations in all answers >3 marks

2006)

Q5) These isomer Q can be tricky – but I just draw myself some diagrams and eliminate the impossible multiple choice answers as I go.

Q28) The image shows a global analysis of ozone – thus they must have used a satellite system. BUT  - you MUST know that TOMS is not longer being used. They are using the OMPS (Ozone mapper profiler suite) on the AURA NPP Satellite. Finally –when it says discuss the ozone hole over Antarctica you must mention general depletion by CFC’s and the ozone hole that forms in Spring. But also NB that there have been some recent signs that the annual hole-size is not getting bigger.

2007

Q15) – I’ve said it enough times above ‘“Cl free radicals catalyse ozone decomposition”…

Q16) b) Once again an extended response question greater than three marks – You must use at least one balanced chemical equation (Eg ozone absorbing UV)

2008)

Q18) b) Apart from drawing a correct diagram of both, the other key things are to:

i)                    Note that ozone is bent and has a dipole, thus it is more soluble in water than oxygen (like dissolves like)

ii)                   Ozone greater size means it takes greater energy to vibrate – thus higher mpt and bpt

iii)                 Note that the single bond in ozone is easier to break then the double bond in oxygen – thus it is more reactive

It is very important to note that it is NOT the polarity or the coordinate covalent bond that makes ozone reactive. Once formed the coordinate covalent bond acts as a regular covalent bond.

Q21) A lot of students skipped this but really – it would have ten 30 seconds to look up the BOS and download a copy. I also wrote a description of the graph in the ‘graph space’ to help you out.

2009) – 2010)

Q12 & Q4 on the topic of naming – please don’t forget all the tricky rules (include hyphens, 2 – di, 4 = buta etc)

9.2.3 HSC Question Feedback

Generally very good.

I was impressed with your mathematical answers. The only concern here was converting between heat per gram and heat per mole (molar heat of combustion).

We have derived the equations for converting these in our notes but you don’t need to derive them I your answers, you can just rely on this equation:

Heat per mole = heat per gram x Molar mass

D_cH = J/g x M  (and obviously this means J/g = D_cH / M)

So the equations you need for heat of combustion are (and you should know most of these without needing to ‘memorise’ them):

q = mCDT

J/g = q/m_fuel

D_cH = q/n_fuel

n_fuel = m_fuel/M_fuel

D_cH = J/g x M_fuel

In the written responses the answers were generally thorough and demonstrated a dee understanding. One major point is that in 9.2.3 we are focussing on the ‘real’ world – ie humans ARE using glucose (from sugarcane) to make ethanol. This is different from 9.2.2 where the focus was on the POTENTIAL to convert cellulose into fuels (ethanol) and materials (ie via ethene) – ie not something that humans are actually doing. So when it comes to discussing ethanol you don’t need to start the process at cellulose (biomass) unless specifically asked.

Tips for specific questions

2002

Q1) Anything above 36^oC starts to harm the yeast (its enzymes don’t function as efficiently)

2003

Q6) This is converting between J/g and D_cH. However, you need to think: Is it easier to convert all four J/g data values to D_cH to find the right one OR just convert the single DcH value to J/g to find the right one?...

2003

Q16) In this questions and ALL fermentation experiment questions – the focus is on i) Did you specify the correct chemicals (glucose, water, yeast) ii) was it an open container & iii) did you specify that you measured the mass before AND after fermenting (ie to measure mass loss). You do NOT need to go into detail about our airlock system UNLESS it asks about how you prevented oxygen entering and proved CO₂ was produced. All you need to say (at the very most) is that “an airlock system was used to allow CO₂ to escape but no air to enter”.

2004

Q25) Whenever you are given a graph (with numerical axes) or a table with numerical data YOU MUST REFER SPECIFICALLY TO THE DATA (ie numbers) in your answer. Eg “ethanol’s heat of combustion is 29.7 kJ/mol compared to octane’s 47.9 kJ/mol…”

2005

Q20) You should be able to do from Glucose to pure ethanol BUT do not start from cellulose (see notes above) – in addition the Q specified for the process in the flow chart and there is no cellulose in the flow chart.

2006

Q2) You need to know that concentrated sulfuric acid is a dehydrating agent (thus used for dehydration of ethanol into ethene). Dilute sulfuric acid is used for hydrating ethene into ethanol (this was the whole focus of our Experiment #3)

Q18) Just be careful to read the question and use your mole ratios correctly – many students were mixing up and finding masses of ethanol rather then glucose.

2007

Q24) a) If you are asked to plot a graph with molar mass or molecular weight as the axid you have to calculate and plot it correctly.

Q24) b) When determining values from a graph you should mark the value on your graph with lines to the axis.

2008

Q22) for this Q I would show the chemical reasons why ethanol is theoretically CO₂ neutral. But then discuss the reasons why it does produce some net CO₂, then I would MAKE A JUDGEMENT on the article. If you do not put a judgement on an assess or evaluate question you will lose 1-2 marks.

Q24) An excellent combination of moles J/g and D_cH. I strongly recommend that you do this question again if you made a mistake. Knowing how to answer this question will greatly increase your understanding of these sort of calculations.

2009

Q17) If you read the question carefully you will see that you have to explain the similarities AND differences between water and ethanol solubility. You need to draw a diagram of both with the polarity labelled. You need to make a statement about like dissolves like. You need to state why both can dissolve polar and hydrogen-bonded substances. But then you need to say why ethanol can dissolve non-polar substances BUT WATER CANNOT – without this last statement you have not explained the differences.

Q20) a) When heat is lost to the surroundings the questions can be tricky. If calculating the heat of combustion this means that the heat you measured will be half what is produced so you need to double the calculated heat of combustion. But if calculating the amount of fuel that must be burned you need to double the theoretical amount of  fuel as half the heat is being lost. This is a question to do again for study.

Q20) b) A real sneaky question – most of the time the two ERRORS are heat loss and incomplete combustion BUT this question wanted two methods to reduce heat loss (only) – e insulate the container and move the flame as close as possible to the container.

2010

Q11) To answer this question you had to think – what chemical decolorises Br-water (alkene) & what chemical is dehydrated by sulfuric acid to make an alkene (alkanol)…

Q23) b) A nasty question. Similar to 2003 Q6 – I would convert the D_cH value to a J/g to figure out which fuel. You should get 36 kJ/g which does not match any of the results. BUT this is the results of a STUDENTS experiment. Thus all the values are going to be UNDERESTIMATES. Thus the student would have always got a number LOWER than the theoretical value – ie lower then 36. So the correct sample must be…

2011

Q17) This is a DEMONSAUD Question - HINT - you have ben given q and DcH for propan-1-ol...what can you find the number of moles of...?

2012

Q30bii) Why might we add ethanol to a solution when trying to dissolve something in water?

9.2.2 HSC Question Feedback

Generally good but some serious misinterpretation of questions and misconceptions

1) We learned two main things in 9.2.2.

a) That biomass (cellulose) has the potential to be converted into glucose, then ethanol (which can be used as an alternative fuel) then ethene (which can be used as a raw material for chemicals). Many people ignored the fact that this cellulose derived ethene was a source of future chemicals

b) That biopolymers (derived from bacteria or biomass nutrients) – eg PHB have been developed over time (ie A. Eutrophus to GM E.coli to GM plants), are biodegradeable, have some limited applications but there are still many obstacles for them to replace petrochemical polymers

2) Biopolymers are not replacement fuels. They are replacement plastics. Technically burning wood (cellulose) is burning a biopolymer for energy but that is not the point of our studies in the Chemistry course.

3) Many students did not ANSWER THE QUESTION. If the question mentions a biopolymer you must talk about PHB, if it mentions biomass you must talk about cellulose, if it mentions current developments you must talk about PHB’s move from A. Eutrophus to GM E.coli to GM plants. If it mentions USES you must talk about specific applications. If it gives you a stimulus (eg a Blog quote) you MUST refer to it in your answer.

4) Make sure you include the CHEMISTRY. You need to demonstrate you are a better Chemistry students than the next person. If you only give a general answer (that any non-Chemistry trained person could write) you will only get (approx) half the available marks. That means write chemical equations, use chemical terms, whrever you can include descriptions of specific chemical compounds and processes.

2002 
Q18) Assess means +, - and judgement. This Q is about developments in a biopolymer thus you need to name the biopolymer (PHB) say how it was originally produced and how advances have increased production rates (ie A. Eutrophus to GM E.coli to GM plants). You should say its applications (and advantages eg biodegradable) and disadvantages ie limited uses and production and a judgement – ie developments have allowed more to be produced but applications are still limited (especially compared to petrochemical polymers)

2003 
Q20) You must note that cellulose if the main component of biomass. You must say how cellulose can be converted into ethanol and how this is a replacement fuel (ie eqn for combustion). You must say how ethanol can be converted to ethene and thus can replace chemicals (eqn good). You must say the advantages – ie renewable, less polluting and disadvantages (eg land use, expense, energy concerns) and then make a judgement (especially in light of crude oil ‘running out’)

2005 
Q18) Again the Q says development so a little on developments (ie making more and using more because we have gone from A. Eutrophus to GM E.coli to GM plants) You then need to say the advantages on the environment compared to traditional (ie renewable and biodegradable) and then the applications and impact on society – but don’t oversell – being used for razor handles etc has not ‘changed the world’ – you could use this as a negative and note its limitations (properties and production) have meant only limited applications. Then give a judgement (ie has potential…)

2006
Q6) we did this Q in class – don’t forget that for condensation polymerisation if you have (n) monomers you lose (n-1) water molecules …

2010 
Q30a) You must show the full equation (reactants and products – with correct formulae) and must label them as condensation or addition

Q30b) We have done this a number of times : to answer this question you need to describe the structure and link this to properties and link this to uses. Also when you name the polymer you must specify which monomer it comes from. VERY IMPORTANT – the bonds between chains are NOT covalent. They are intermolecular bonds and are usually weak dispersion bonds (but because the chains are so long these bonds are quite strong overall), but can be H-bonds when there are OH groups in the chains (eg cellulose).

You need to choose three different polymers but at least one needs to be from ethene and one from glucose.So, what polymer comes directly from glucose? Then I would choose two of the polymers that start with ethene - you could possibly get away with ldpe and hdpe but BOS might count them as the 'same' polymer...

2011
Q27) Be careful to read the Q – you had to include USES (2nd word of question) of a NAMED biopolymer (ie you had to say PHB) you had to mention the properties of both polymers (eg biodegradable vs non-biodegradable) and refer to the blog. Better answers noted polystyrenes properties and uses and noted that they were short term uses but because they were non-biodegradable they had specific impacts on living systems (ie relate to blog quote). They then contrasted this to PHB’s properties and applications and biodegradability noting the possibility of less environmental impact.

9.2.1 HSC Q Feedback

Generally very good and thorough answers.

Most lost marks were due to misreading the question, not fully interpreting the question or through not giving enough critical Chemistry details.

Tips on how to improve your answers are below as well as details about some misconceptions (critical that these are overcome ASAP).

2002
Q16c) Equations for alkene reactions MUST be full structural equations (see here). BUT – be careful – you can use the completely summarised structure without drawing in all the C’s and H’s BUT if you draw in the carbons you must also draw in all the hydrogen. In addition it is very important to get states correct. Just ONE state missing or incorrect can lose you a mark. HINT: the cyclohexene is liquid, the bromine is aqueous, if you have 1,2-dibromocyclohexane as a product it is liquid (it cannot form H-bonds thus will not readily dissolve in water) BUT if you have 2-bromocyclohexanol as a product then it will be aqueous.

17) Be very careful to fully answer the question. Because it asked you to explain why the physical properties were similar but the chemical properties were different you had to do both. Both alkenes and alkanes are covalent molecular hydrocarbons thus they both have similar physical properties are non-conductors with low mpt and bpt. However, alkenes C=C double bond allows it to undergo addition reactions making them more chemically reactive then alkanes which only have single C-C bonds. NB the emphasis on the key chemistry facts: alkenes, C=C, reactive (addition) & alkanes, C-C, less reactive

2003
17b) Describe means you need to give some chemical detail. Identifying it is addition polymerisation is one mark. For the full marks you need to specify the process of how addition polymerisation works, give an equation for the reaction and or the specific details of LDPE vs HDPE manufacture

17c) We went over the phrasing of this in our notes and Experiment #2 “The chaotic natur of addition polymerisation means activated chains of different length collide and terminate, thus resulting in a polymer with a distribution of molecular weights”

2004
17a) If the question asks for ONE answer give one answer. Also if it asks for the common name and you give BOTH the common name and systematic name you will get zero as it shows that you do not know which is which. For the record (common/systematic): vinyl chloride / chloroethene & styrene / ethenylbenzene

17b) Because it said ‘discuss’ you need to give a little more then just a link between property and use. For the three marks: name the polymer (eg polystyrene), identify a property (when expanded it is tough and lightweight), link it to a use (thus used for packaging to protect goods), contrast to a different application (but when non –expanded it is clear and rigid so used for CD cases).

17c) i) READ THE QUESTION – draw the POLYMER (ie at least two repeating units). ii) polymers are so long that they form tangled chains with LOTS of interchain bonds. They are solids, not gases.

2005
16c) Be specific when referring to the method. We used 2ml of each chemical ONLY for safety reasons. You must say that we used identical volumes (for validity) so say the exact amount “we used 2ml each of cyclohexene and cyclohexane”, is better and quicker than writing “we used equal volumes of of cyclohexene and cyclohexane”.

2006
20) A 7 mark question will likely be the biggest question in the paper. This is the sort of Q where the band 5’s are separated from the band 6’s. So in these Q you have to do whatever you can to distinguish your answer from the rest of the state. The Q had four main parts

i) Why ethylene is important – ie telling you must have an intro describing what ethylene is (structure) noting the double bond, noting it is reactive and can undergo addition reactions

ii) Describe new materials – ie NB that addition reactions can make a range of chemicals eg halogenated hydrocarbonds (refrigeration), but the big focus should be on addition polymerisation (ie making the monomers styrene, vinyl chloride) and the polymers PS, PVC , LDPE and HDPE

iii) Making fuels – we know that ethanol for fuels comes from fermentation BUT - do what the question asks – details how ethylene can be turned into ethanol

iv) Use equations (and because the Q specified equations they must be balanced HAVE states and there must be more then one)– eg hydration of ethylene to ethanol (with states and catalyst), addition polymerisation of ethylene into polyethylene.

2007
26) polyethylene and polystyrene come in two different structural types with different properties and applications. Thus link the structure to properties to uses for EACH of LDPE, HDPE, rigid PS and expanded PS = 4 marks. Misconception alert. The benzene ring makes the polystyrene chains lock together making non-expanded PS quite rigid. BUT when expanded the properties are dominated by the air bubbles in the structure (it is effectively a composite of air and PS). You do not need to know the explaantion for why the properties change so dramatically when expanded (beyond having the air make it less dense) but it is important that you understand that the air does NOT act as a plasticiser and make the chains slide easier.

2008
16b) You had to mention the three chemicals you used and the alkene and alkane had to be corresponding (eg cyclohexene and cyclohexane), you had to say what you would OBSERVE to distinguish them (ie in cyclohexene the colour of the bromine water went brown to clear) and you had to include a fully balanced, structural equation with correct states (see 2002 Q16c above).

2009
6) Read the question carefully. Unsaturated means it has double (or triple bonds) and thus there will be an ADDITION reaction!

19) Read the question i) ‘physical and chemical processes’ & ii) ‘from a raw material’. Raw material means something found in nature. Some interpreted this to mean cellulose and they did the whole cellulose to glucose to ethanol to ethylene description – this is fine but the problem is that we don’t make ethylene that way (yet). So you had to start from CRUDE OIL. From there you had to describe each of these processes i) fractional distillation (P), ii) cracking (C), iii) addition polymerisation (C), iv) shaping/moulding into a bottle (P). NB LDPE & HDPE are thermoplastics so they can be molten and shaped. BIG MARKS = USE AT LEAST ONE CHEMICAL EQUATION

2010
Q24b) Whenever you get a question about distinguishing alkenes vs. alkanes you should ALWAYS use the Br water experiment. Why not bubble the gas through Br water and if it turns clear that means some ethylene is still present. If it stays brown that means only ethane is present….

2011
1) READ THE QUESTION CAREFULLY!

Intro to Radioactivity

Welcome back everyone.

Here is a nice little video from TED ED - should watch before Week 2

This video below also caught m eye on TED ED. It is pretty amazing that a parasite can actually CONTROL THE BRAIN of its host and make it do its bidding!!!

But while the video below is great this list is what blew me away - the degree of control that parasites can have over their hosts is incredible. My favorite is the fungus that controls the minds of ants...

Merry Christmas Everybody

Enjoy 'The best Christmas song ever. Period.'

9.4.4 Feedback

PART 1  - THE ATMOSPHERE

1)   9.4.4.1.1 Describe the composition and layered structure of the atmosphere

 (A) Of all the ozone in the atmosphere, 10% is found in the troposphere. This is not the same as saying ‘10% of the troposphere is ozone’ (it would be hard to squeeze in that 10% considering that ~80% of the troposphere is N₂ and ~20% is O₂)

(P) Be careful with your diagrams, the layers of the atmosphere get thicker (in km) as you head toward space – your diagrams don’t have to be to scale but they should reflect this. Also, make sure the ozone layer is IN the stratosphere, it does not take up the whole stratosphere.

2)    9.4.4.1.2  Identify the main pollutants found in the lower atmosphere and their sources

3)     9.4.4.1.3   Describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant

(Q) Always include the ^● for free radicals (even O^●)

(R) When discussing the dangers of UV, it is important to mention both its effect on plant photosynthesis and on animal cells (e.g. sunburn, DNA damage, skin cancer).

PART 2 – THE OZONE MOLECULE

4)   9.4.4.1.4  Describe the formation of a coordinate covalent bond

(B) Remember from yr 11 – All atoms ‘want’ to get a ‘full outer shell’ of electrons (ie a ‘noble gas configuration’). Non metals can obtain this stable full outer shell by gaining electrons or by sharing them with other non-metals (ie forming a covalent bond).

(C) Always draw ozone with its bent shape. It is an important structural feature. It is also important to draw all the electrons in their correct positions around each atom.

5)     9.4.4.1.5   Demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures

(S) Be careful, a single covalent bond has a PAIR of electrons being shared (ie one from each atom). This means there are four shared electrons in an…

(X) Lewis dot diagrams need the square brackets [ ] around ions with the charge specified e.g. a sodium ion is [Na]⁺. For clarity it can help to draw the electrons for each atom with different symbols (eg x, o, ●) and it is advisable to label the coordinate covalent bond. See here for the correct way to illustrate the fomation of a polyatomic ion with a coordinate covalent bond).

6) 9.4.4.1.6     Compare the properties of the oxygen allotropes O₂ and O₃ and account for them on the basis of molecular structure and bonding

(D) It is vital to define all Chemistry terms properly. You need to know the correct (thorough) definition of allotrope.

(E) There is nothing wrong with putting the actual values for O₂ and O₃ desnity, solubility, mpt and bpt in your table but you DO NOT need to know these values – just that O₃ has higher values than O₂.

(F) O₂ and O₃ have a low mpt BECAUSE they are covalent molecular ie they HAVE have weak intermolecular bonds which require LITTLE energy to break allowing the molecules to separate. ALSO - because thye have low bpt they are gases - because they are gases they have low density.

(G) You need to explain the differences in mpt, bpt and water solubility for O₂ and O₃. Firstly, O₃ is slightly polar (ie has dipole-dipole intermolecular bonding as well as weak dispersion) due to the uneven distribution of electrons in the molecule – thus it forms slightly stronger bonds with water molecules (a polar solvent, like dissolves like) and thus has higher solubility). This stronger intermolecular bonding, AND because it is a larger molecule requiring more energy to vibrate, means it takes more energy to separate the molecules giving it a higher mpt and bpt.

(H) The single covalent bond in ozone is easier (take less energy) to break than the O=O double bond. Thus O₂ which only has the O=O double bond is less reactive then O₃.

(T) It is vital to know the difference between intermolecular and intramolecular bonds. Clearly, these terms only apply to covalent molecular substances (the only substances that are ‘molecules’, not ‘lattices’) – so the strong intramolecular bonds are the covalent bonds between atoms and the intermolecular bonds are the weaker forces (bond) between molecules (eg hydrogen bonding… & …).

(Y) Oxygen free radicals don't have a measured bpt and mpt etc because to measure these values you need to have a number of them together - but as soon as you out these reactive molecules together they react to form O₂ preventing the properties of O^● being measured.

(Z) To compare the strucutre of O^●, O₂ and O₃ you need to detail their # atoms, intermolecular bonds, types of intramolecular bonds (v. imp!) and draw a Lewis dot diagram. NB - sometimes you will see ozone drawn with two single bonds and a 'dotted arch'. The dotted arch is called a ‘resonance bond’ – we don’t worry about that in yr 12 HSC Chem – just draw it with the bent shape and with ONE double bond and ONE single coordinate covalent bond.



7)     9.4.4.1.7   Compare the properties of the gaseous forms of oxygen and the oxygen free radical

PART 3 – CHLOROFLUOROCARBONS & IMPACT

9)     9.4.4.1.8      Identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere

10)      9.4.4.1.10   Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems

(I) The ozone hole is a seasonal (Spring) event in the Antarctic where there is rapid depletion of O₃, forming the ozone ‘hole'.** Ozone depletion refers to the general decrease is global O₃ concentrations that have occurred over the last 40 years.
** NB when the ozone hole 'breaks up' in late Spring, severly ozone depleted air can spread north to Southern Australia.

(J) The cold dark Antarctic winter results in ‘ice’ crystals forming in the stratosphere. These ice crystals catalyse the reaction between chlorine nitrate and hydrogen chloride to form hydrogen nitrate and chlorine gas. It is this chlorine gas that decomposes to produce the chlorine free radicals when the sunlight returns in spring (the large amount of Cl^●  results in rapid ozone depletion and the ozone hole)

(U) You must mention (along with your series of equations) that the Cl^● CATALYSES ozone destruction (ie it takes part in the reaction, providing a reaction path with low activation energy and thus increasing the rate of reaction, but it is reformed and not consumed in the reaction)

11)    9.4.4.2.1     Present information from secondary sources to write the equations to show the reactions involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere

12)      9.4.4.1.11    Analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained

(K) Dobson spectrometers monitor a wavelength that O₃ does and a wavelength that O3 does not absorb – by comparing their relative intensities the concentration of O₃ can be calculated. Similarly satellite systems monitor wavelength of light that ozone does and does not scatter to determine O₃ concentrations. There is a nifty little video about this here: http://www.youtube.com/watch?v=BCAQR-4ue0U

(L) You need to know at least one advantages and one disadvantage of balloons, Dobson spectrometers and satellite-based spectrometers. Also: Nimbus, Aura and Suomi-NPP are satellites, TOMS, AURA and OMPS are the ozone monitoring instruments they carried (respectively). The one being used now is OMPS. If you talk about TOMS you sound outdated and will be penalised for not using reliable (ie current) resources). There is a nifty little video about this here: http://www.youtube.com/watch?v=BCAQR-4ue0U

13)    9.4.4.2.3     Present information from secondary sources to identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs

(M) When comparing CFC’s, HCFC’s and HFC’s:

a) Say what atoms they contain

b) Note that Cl is the halogen that damages ozone

c) NB that HCFC’s decompose in the troposphere (so little reaches the stratosphere) but NB they have some ODP (and define this the first time you use it) because thye still contain Cl

d) NB that HFC’s have no ODP because…

(N) When writing a criteria, be smart and be specific. Rather then saying that “One criteria to be examined is the ODP”. Say “To be a successful replacement, the chemical must have low to no ODP to overcome the problems produced by CFC’s” – after that, if you say that HFC’s have no ODP you have addressed the criteria and it is clear that HFC’s are a good option.

(O) When assessing the Montreal protocol, you should consider the fact that it has been followed worldwide, and that CFC’s use and productions rates have dropped and that Cl concentration in the atmosphere has started decreasing and that O₃ concentrations are currently relatively steady.

(V) When you state that CFC’s continue to be released into the atmosphere  despite the Montreal Protocol (and thus the recovery will be slow), you need to specify that this is from old disposed CFC’s containing equipment in landfill

14) EXTRA – you DO need to know ppm and ppb in the HSC course

(W) – Oops, the answer to (a) should be 0.2 GRAMS, and (d) should be 0.013 ppb (read the Q Dr Blurg!)

Goodbye again. Goodbye for now, class of 2012

It was great to see the Chemists and Physicists of the class of 2012 again today.

As I said to those who I managed to speak to -  I was made to feel so welcome and had such a great time teaching you this year – thank you for making the year so special.

BUT – I was startled by the revelation that “..I enjoyed your jokes and your sometimes inappropriate humour…”
Firstly - Thank you. (I was touched by this and the whole message).
Secondly - Woah! - I had gone to great lengths to walk on the right side of clean this year. I can’t think of anything that wasn’t …However, if this is what was being referred to:

I can assure you that anything I said was completely innocent and that any double entendre was a construction of YOUR imaginations!

But on that topic of inappropriate humour, I have recently decided that Bill Burr is one of the funniest comedians I have heard in a long time. The audio track to this video (YouTube link to 'Bill Burr : Let It Go' removed due to inappropriate humour)  is great for a car trip (though make sure everyone in the car is over 18 and not easily offended) – and no, there is no way I would post the actual video to the Blurg.

What made me laugh the most was the bit between  7:35 and 7:55 (this is how I felt trying to field some of your questions this year - but I'm not complaining - you have helped me become a better teacher/chemist/physicist).

Best wishes, please keep in touch – I’d love to hear what you are studying and where your career path takes you.

Merry Christmas,

Dr Blurg

Portfolio Experiment #20

Worksheet Feedback

Q1) When you are asked to compare two things in Chemistry you need to communicate the meaning (definition) of both things AND the similarities & differences between them. Considering that CFC’s are a special subset of haloalkanes it would be easier to define what a haloalkane is and then the comparative definition of the CFC. Eg “Haloalkanes are alkanes (single bonded hydrocarbon chains) that have…. However, CFCS….”

Q2) Don’t forget: you need to use di, tri, tetra etc if there are multiple of a halogen; you need to give the lowest numbers to the FIRST ALPHABETICAL halogen IF there are two equivalent numbering systems; & you need to always name the halogens in alphabetical order.

Eg for the compound below, numbering from either end gives the same set of numbers. So we give the first alphabetical halogen (chlorine) the smallest number - BUT - we still name it in alphabetical order.

So the name is...(highlight the space below to check your answer)

2-chloro-3-fluorobutane

BTW - there is currently a lot of controversy about this at the moment - the above explanation is correct according to IUPAC and RACI but this WAS NOT one of the provided answers to a MC question in the 2012 HSC Chemistry paper. Dr Blurg (& I imagine a lot of other teachers) contacted the BOS about this and they released a statement the essentially admitted their error in early 2013. Go Dr Blurg!
Q3) Yes you need to use the correct chemical symbols and include all the hydrogens.

Q4) Make sure you read the question (ie name…) and also see the tips for Q2 above.

Q5) See tips for Q2 and Q4 above.

Q6a) See (general) tips for Q1 above

Q7) The whole 9.4.4 focus area is about how Cl free radicals catalyse ozone decomposition. Thus, when it asks why HCFC’s are being phased out and why HFC’s are preferred you need to make sure that your answer clearly explains this in terms of Cl.


Summary Feedback

A) When presenting your rules you need to be thorough. Eg don’t forget to:

* Say what needs to be named alphabetically.
* Define the prefixes to use (up to five min).
* Define what is meant by ‘lowest total’ numbers.
* Specify what has to be done if there are two equivalent numbering systems - Hint it is NOT to give preference to the most electronegative halogen!
* Identify where commas and hyphens are needed.

B) In the risk assessment you need to consider why you need to pick up dropped pieces and why you should not use your mouth to separate the models.

C) Make sure you use correct naming when naming your examples and isomers. Don't make it difficult for yourself. Put all the halogens down one end so there is no confusion about the end to name from.

D) Be careful to be exact with your definitions. Eg you need to indicate that in CFC’s chlorine AND fluorine have replaced ALL hydrogen atoms (ie they contain chlorine, fluorine and carbon atoms only). Make sure your example chemical matches the definition.

E) All required structural diagrams must be submitted (hand drawn).

F) For the last question of the Theory section you needed to draw AND name THREE isomers AND the original haloalkane.

G) Isomers have to have exactly the same number of each atom in the molecule.

H) Don't forget to include a specific application of the CFC you chose.

This summary and worksheet was done very well - AND the class got its first 'full-mark' draft - impressive. Just like the comics below!

And as this is the last 'official' post before Christmas - "MERRY CHRISTMAS BLURGLINGS"

Enjoy this little game and the pics below

Portfolio: Experiment #3

Modelling in Modern Chemistry

Last year, scientists in Mexico have used microscopic polystyrene spheres to model how atoms bond (ie 3D shapes) AND model the polymerisation process. The video below shows the particles behaviour in the modelling experiments and the article found here has a good discussion about the advantages of this type of modelling in Chemistry - ie it relates to Skill 14.1f that we are studying in this experiment.



From our modelling

HYDRATION

 

From our modelling

DEHYDRATION

 

 

Worksheet Feedback

These tips should help you to correct your worksheet. Relevant number codes are written on your booklet.

Q2 & Q3) The hydroxyl group has its free electron on the oxygen ato so be careful to show the bond between the carbon and hydroxyl actually connecting the C to the O, not the H.

Q4) Boiling and melting are physical changes. They do not involve chemical bonds breaking. They involve INTERMOELCULAR bonds breaking – ie the bonds between molecules. Thus substances that form very strong intermolecular bonds have higher mpt and bpt than substances that form weak intermolecular bonds. In order of strength of intermolecular bonds: Hydrogen bonds > dipole-dipole>weak dispersion. ALSO to compare alkanols and alkanes properly you need to outline the different intermolecular bonding that both can form.

Q5 & Q6)
* When talking about solubility you should always say like-dissolves-like, & say whether the solute and solvent are polar or non-polar and then say whether they are soluble or insoluble. For alkanols as the C-chain length increases the hydroxyl group becomes less significant thus the chain is less polar…

* Ethanol has a polar component (OH) and a non-polar component (the alkyl group).

Q6)
* Answer the whole question. It is OK to say why ethanol is miscible in water and hexane, but you have to explain why hexane and water are not miscible. NB molecules CAN FORM intermolecular bonds, they cannot ‘have’ or ‘contain’ them.

* There is a big difference between a hydroxide ion and a hydroxyl group. See the first page of our 9.2.3 notes.

Q7 & Q8)
* Always draw structural diagrams for carbon compounds (including addition and dehydration reactions) and always include required catalysts and states. The only reactions you DON'T need structural equations for are fermentation  & combustion.

Q8)
*For alkanes, alkenes and alkynes for 1-4 carbons atoms they are gas, above that they are liquids (eventually solids but we don’t need to worry about that transition). However, because alkanols have hydrogen bonding between their molecules they are liquids (ie methanol, ethanol… are liquids)

* The naming on that sheet was very bad. 8d should have been PROPENE (there is only one isomer = no need for numbers).

* For dehydration you need a concentrated sulfuric acid catalyst, for hydration you need dilute sulfuric acid. Also note that many hydrations and dehydrations can result in two different products. Eg hydration of propene could produce propan-1-ol or propan-2-ol.

* Dehydration will only convert an alkanol to an alkene with the same number of carbons. It will not crack it into ethylene molecules. Eg pentan-1-ol will dehydrate to pent-1-ene.

* Include names remembering the correct naming has the number before the –ol or –ene NOT at the start of the name.


Summary Feedback
A) The catalyst for ethanol dehydration is CONCENTRATED sulfuric acid. Hydration of ethylene requires heating it and water in the presence of a DILUTE sulfuric acid catalyst.

B) For the explanations make sure you say why using ethylene to produce ethanol is non sustainable AND why we need renewable sources of ethylene (i.e. why we need ethylene and why making it from ethanol is sustainable). In addition - you must show how ethanol is renewable - ie it is made by fermenting ??? which comes from ??? during ???.

C) Using colours to highlight the species that change positions make it easier to see where the bonds are being broken and remade (i.e. especially the H, OH that are involved in bonding). - BUT YOU MUST USE SOME SORT OF KEY. Eg you might use a circle to indicate hydrogen, but for one that takes part in the reaction you might put a pink mark next to, the other a blue. Thus you can see exactly where these two H atoms go in the reaction.

D) You need to show all the intermediate steps to show how the catalyst reacts to make intermediate products and then reforms. Using arrows (and colours as described in C) will help make this clear.

E) You need to include TWO advantages and TWO disadvantages You must refer to BTH the Molymod and the computer animations. A big advantage of this modelling as that it enabled you to see how the catalyst played a role in the reaction! Hints for disadvantage: did it react spontaneously as in real life. Were you bale to model the individual electrons, did the models really show the correct size and position of atoms and bonds…

F) Catalysts increase reaction rate BY reacting with the reactants to produce… At the end of these intermediate steps the catalyst is…

G) It is not enough to say that using HX was simpler. You need to say WHY it was valid to simplify it as HX – you must relate it to what happened in the reaction.

H) Use structural equations & states. NB the ethanol dehydrated starts off as pure ethanol. The ethylene is a gas and being non-polar will not dissolve in the water (ie cannot be aq).

I) Hydration of ethylene does not involve cracking. However, cracking of crude oil fractions was used to produce the ethylene which was then hydrated (in an addition reaction with water) to produce ethanol.