Portfolio: Experiment #2

PORTFOLIO #2 Feedback on Worksheets

 Q1)
*You do not need to know the details of the reactions to make styrene and vinyl chloride but you do need to know the reactants – they are in our notes.

*Styrene is NOT used for insulation (or esky’s, CD cases etc…). However polystyrene is. So you need to say that styrene is used as the monomer for polystyrene and that polystyrene is used for insulation… i.e., is near enough good enough for Chemistry? – see below

Q3)
*It is good that we understand the connection between

Production conditions (which determines)
=> structure (which determines)
=> properties (which determines)
=> uses.

But when explaining one of these features - e.g. properties – you must primarily relate it to the factor that directly influences it. Eg properties are determined by structure;  uses are determined by properties. SO - when explaining why LDPE is non-crystalline, explain it in terms of its branched structure (if required you can then go and relate this back to production conditions, but the main focus of your explanation should be the connection between structure and properties).

* Cellulose is not water soluble. Paper does break up in water but the cellulose itself is not dissolving. The term that people were looking for is biodegradable (basically able to be eaten by bacteria) cellulose (paper) is but polyethylene is not.

Q4)
Similar to Q3, these are questions about properties so you relate the answers to their structure. It is important that you understand that the further apart chains are, the weaker their inter-chain bonding (intermolecular weak dispersion forces) is. Thus strength and melting points are lower

Q5)
For the last two columns it is important that you link an appropriate PROPERTY to the use. It is no point saying that polystyrene is used for packaging because it is a thermal insulator. Say it is used for thermos insulation because it is a thermal insulator OR say it is low density and tough so used for packaging. It is also important to distinguish between non-expanded and expanded polystyrene when discussing its properties and used (ditto for plasticised and non-plasticised PVC).

PORTFOLIO #2 Feedback on Summaries
Again – very well done – just that I think everyone is still trying to use too many words. I’ll try and give some tips below to help.

NOTE – please use the term ethylene NOT ethene (ethene is the systematic name but the IUPAC name is ethylene)

(A) With the safety you need to say the danger AND specifically how to avoid the danger – ie things you should and shouldn’t do.

(B) In the method the dice rolling modelled the chaotic nature of the addition polymerisation process. You do not need to record the dice roll numbers used. You do need to say that ‘different’ dice rolls resulted in initiation, propagation, termination and backbiting (for LDPE models only).

(C) A free radical is a chemical species that has an unpaired electron (and is thus very reactive). Technically a free radical is a chemical species with an unpaired electron that could be formed by splitting a molecule.

(D) It is important to note that initiation in LDPE is started when the organic peroxide REACTS with the ethylene monomer by breaking the double bond and forming a free radical. HDPE is initiated by the ethylene monomer forming a temporary bond with the catalyst (which could be metallocene or Ziegler Natta), which breaks the double bond and forms a free radical.

(E) Diagrams have to at least be big enough to see. If you got an (E) code they need to increase in size.

(F) To explain the distribution of chain lengths the best phrase I have come across is “The chaotic nature of the polymerisation process means activated chains of different length collide and terminate. Thus producing a polymer with a range of chain lengths”.

(G) Question 6 & 7 need you to EXPLAIN the differences and similarities – I think this is where you can express your understanding more succinctly. Eg Q6 “LDPE and HDPE are both covalent molecular and thus they have no free electrons to conduct electricity. HDPE has linear chains allowing for close crystalline packing and high density. The close packing means there is strong inter-chain bonding and thus HDPE is strong and rigid. LDPE…”
For Q7 you can choose your words carefully to be thorough yet concise. Eg Q7 “LDPE’s branched chains and non-crystalline low density packing mean it is flexible and transparent, making it suitable for cling wrap and plastic bags…”
Remember you DON’T need to detail EVERY application, just a few illustrative examples.

(H) When assessing whether model kits can effectively illustrate formation you need to consider whether they were able to show initiation, propagation and termination. It does not matter whether you think they can or can’t do this effectively as long as you say which and provide a reason.

(I) In general, pictures are useful in chemistry for effective communication. When dealing with complex formulae or concepts, diagram are quicker and easier to prepare (presenter) and understand (audience).

(J) When assessing whether model kits can effectively illustrate properties you need to consider whether they were able to show the (similar and different) physical and chemical properties of the polymers (strength, flexibility, mpt, bpt, conductivity etc).

(K) Not only did you have to say how pictures are useful for communicating chemistry concepts in general – but you also needed to give an example of where they were useful in this experiment (including the summary – perhaps read (L) below for an idea).

(L) You do not need to spend time (and use valuable space) describing initiation, propagation and termination in the text as long as you have properly labelled diagrams (ie see (I) and (K) above).

(M) You cannot explain backbiting properly unless you have four pictures.

(N) Remember – the rules of the assessment are size 10 Arial narrow, single spacing with 1cm margins. You would not want to have a summary inadmissible because of a formatting ‘error’.

(O) You must be specific about which properties are controlled by which bonding. You are not demonstrating understanding if you list a whole lot of properties: eg "They are insulating, insoluble, low mpt, .... this is because they are covalent molecular and have weak dispersion bonds". in such an answer it is not clear which type of bonding controls which property and why. Also NB they are insoluble because they are non polar CM but also because the long chains are tangled together (hard to separate) - this (and the large molecule size) also keeps their mpt and bpt higher than other CM substances as well.

Oil and Ethanol

These videos are all do do with the global oil supply and the potential of ethanol.

1) 300 years of fossil fuels

2) ABC Catalyst Peak Oil Report

3) Brazil & ethanol

4) Ethanol's future

5) TEDx - The Physics of renewable energy - is it possible?

6) TED - Transition to a world without oil

7) Arguments against ethanol

8) & this song is about ethanol and is one of the most awesome songs ever - it is a shame that learning to sing this is not part of the HSC Chemistry course

Portfolio: Experiment #1

Notes from today's lesson here

Experiment results

a) The chemicals before mixing - note the colours

Br-water

                                                                   

Cyclohexane

Cyclohexene

b) The chemicals immediately after mixing - are there any differences?

Cyclohexane and Br-water (immediate)

Cyclohexene and Br-water (immediate)

c) The mixtures after 10, 15 and 20 minutes

Cyclohexane (a) &
Cyclohexene (e)
10 min after mixing with Br-water

Cyclohexane (a) &
Cyclohexene (e)
15 min after mixing with Br-water

Cyclohexane (a) &
Cyclohexene (e)
20 min after mixing with Br-water

Things to ponder

i) Which chemical reacted more rapidly with the Br-water and what evidence led you to that conclusion

ii) Why were two layers formed when the chemicals were mixed (ie why were they immiscible)?

iii) Which layer was on the bottom and why?

iv) The cyclohexane layer got browner over time suggesting that the bromine was dissolving into it - why is bromine soluble in cyclohexane?

v) For the same reason as (iv) bromine should also be soluble in cyclohexene - why didn't the cyclohexene turn brown?
vi) For the chemical that reacted with bromine water - can you name and draw a structural diagram of the product?



Using a control
In the fume cupboard were three extra test tubes:
*One with just cyclohexane
*One with just cyclohexene and
*One with just Br-water

They just sat there and weren't mixed with anything. Throughout the whole time the Br-water stayed brown and the cyclohexene and cyclohexane stayed clear.

Thus, by comparing our results to the control, we can be sure that the change in colour was due to the reaction between the cyclohexene and the Br-water, ie not just due to some other environmental effect or because the Br-water naturally changes colour.

Reliability
We repeated the experiment with consistent results AND we can use other secondary sources to check the reliability of our results. See the clips below

PORTFOLIO #1 Feedback on Worksheets

MOST IMPORTANT TIP – DO NOT EVER leave any of these questions blank. They are a compulsory part of the coursework and are a prerequisite for getting your draft summary marked. IF you cannot do a question you need to:

• Look up the answer in your notes/text
• Ask a classmate
• Ask Dr Burg

Then you need to do the question

 Q2)

When a question states structural formula and names you have to give structural formula AND names - amazing! Also – unless you have finished you HSC exam you are obligated to put ALL the hydrogens on ALL your carbon chains. Seeing students take shortcuts in these practise questions makes me want to use octane, nonane and decane for ALL hydrocarbon questions in your exams. You have been warned.

  

Q3) & Q5)

For combustions make sure you balance the carbon , then hydrogen, then oxygen (CHO)

Q4)

Remember that in substitution reactions (for alkanes) only ONE species is added to the chain in the place of ONE hydrogen (i.e. the hydrogen is substituted for something else)

  

Q6)

Alkenes undergo addition reactions. TWO species are added to the alkene AT THE SITE OF THE DOUBLE BOND. Thus, if the double bond is between the first and second carbon, the species added will be on the first and second carbon. In addition reactions (unlike substitution reactions) only one product is produced.

  

E.g. if chlorine gas is added to 1-pentene the product will be 1,2-dichloropentane.

NOTE: there is commas between numbers and hyphen between letters and numbers when naming

  

E.g. if water is added to hex-2-ene (with a sulfuric acid catalyst) we are adding a H and a OH group to a hexene chain with a double bond between the second and third carbon. Thus the OH will go on either the second or third carbon. So the product could be hexan-2-ol or hexan-3-ol.

NOTE: When adding asymmetrical molecules (water, HCl, HBr etc) to alkenes bigger than ethylene there are always two possible products

  

Q7)

 *It is important to include any necessary catalysts for these reactions.

  

* Sometimes there will be more than one way to make the chemical.

  

* You need to make sure your equations are balanced. It is easier to do this if you draw and think about the structures.

  

E.g. If I want to make 1-bromobutane (CH2BrCH2CH2CH3) from but-1-ene (CH2CHCH2CH3) I need to add an extra hydrogen and a bromine atom. Thus I have to react the but-1-ene with HBr!

Q8)

Where the table says ‘Burns’ it means ‘Combusts’ – so most people still need to write the combustion equations for pentane, hexane and ethanol. Balancing combustion reactions is something we all need to practise (CHO!)

PORTFOLIO #1 – Feedback on Summary Sheets

Note – these summaries were very well done. The addition (lol, that’s very punny Dr Burg!) of skills to this experiment summary made it quite challenging and you all did very well. I had to increase difficulty of the marking scheme to distinguish between you.

NOTE – in this experiment decoloured (which means REMOVE colour) is a better term to use than discoloured (which just means CHANGE colour).

(A) There is something in Engineering (and Science) called the KIS principle (Keep It Simple). Don’t say more than you need to. Answer the question and that is it. You only had to explain why alkenes are more reactive than alkanes. Eg “Unlike single-bonded alkanes, alkenes have a carbon-carbon double bond that allows them to undergo addition reactions. Thus, alkenes are more reactive than alkanes.”

(B) The dependent variable is the factor that is measured in order to determine how it responds to changes made to the independent variable (i.e. the value of the dependent variable DEPENDS on the independent variable) . In this experiment the dependent variable is the reactivity of the molecules (which we measured by the rate at which they decoloured bromine water).

(C) We need to control all variables other than the DV and IV to make the experiment valid – ie so that measured changes to the DV are ONLY due to the changes made to the IV. Some examples from this experiment include temperature, time of measurement, light intensity, and the fact that we used corresponding molecules (same # of carbons with the same shape).

(D) A control is a sample that is left unchanged so that all other results can be compared to it (ie to determine if the IV really had any effect on the DV). In this case we left samples of bromine water, cyclohexene and cyclohexane unmixed over the same time period as the experiment. The fact that they did not change colour indicates that the observed colour changes in the experiment were due to the reaction between cyclohexene and bromine water.

(E) Make sure you name the reactants and products. Remember that when naming hydrocarbons there are commas between numbers and hyphens between letters and numbers. Eg CCl3-CClF2 is called 1,1,1,2-tetrachloro-2,2-difluoroethane. Also - bromine (the element) is a liquid but bromine water is a aqueous solution of bromine – ie Br2 (aq)

(F) Even though cyclohexane was the only chemical identified as being dangerous for the environment, we should never tip harmful chemicals down the sink if we can avoid it. All three were stored for proper disposal.

(G) Reliability is a measure of whether the results are reproducible. This requires the experiment to be repeated with consistent results. Validity is a measure of whether the investigation was able to measure what was intended. The most important way to ensure a valid experiment is to ensure that all variables are controlled so that the only thing affecting the DV is the chnages made to the IV (but it also requires accurate measurement and reliability).

(H) Don’t forget that we did the experiment in a fume cupboard!

(I) A cause is a REASON for something happening. An effect is what happens as a RESULT of the cause. A great ay to explain a cause-and-effect situation is this awesome word: ‘because’ (it introduces a cause). Eg “Because alkenes have a reactive double bond (the cause), they undergo an addition reaction with bromine water (the effect)”.

(J) To explain reliability we need to consider whether we repeated the experiment with consistent results. Even though no individual in the class repeated the experiment, each group did the same experiment and all groups obtained the same result.

(K) You have been asked to write four different conclusion sentences (from slightly different perspectives). You need to treat each as if it was a stand-alone conclusion. So each needs to say (somehow) that the cyclohexene reacted faster than cyclohexane with bromine water and thus that alkenes are more reactive than alkanes.

(L) Quantitative results involve measured numerical values (quantities, eg mass, time, volume). Qualitative results involve descriptive measurements of observations (eg colour, shape, size, identity).

(M) You need to include labels on your diagrams. If your diagrams are not coloured you need to label the colours. You should label that the bottom layer was always the aqueous (bromine water) layer. It is important to note that the hydrocarbon layer NEVER mixed with the aqueous layer (remember ‘like dissolves like’). Even when the bromine water was completely decoloured there were still two layers: a clear cyclohexene mixture on top and a clear aqueous mixture below.

(N) It is a good idea to make your safety section concise by combining all the similar risks together but be careful not to make erroneous statements. Eg you cannot say that the bromine water risks and precautions are identical to cyclohexene, as cyclohexene is flammable and bromine water is not.

(O) All hydrocarbon reaction equations (apart from combustion, photosynthesis and fermentation should be structural equations - with states.

(P) You need to make your statements generalised - ie we studied this one simple system of cyclohexene and cyclohexane (ignore the hexane) so we know that the only thing affecting the rate of reaction is the double bond. Thus, we can conclude more than just cyclohexene reacts faster than cyclohexane - we can make the generalisation that alkenes are more reactive than...

(Q) Specify what your controlled variables were

Physicists: Q: What now for the LHC?

A: AWESOME STUFF!

It has already proven the existence of the Higgs boson but now the focus is on even more amazing things:

* Is gravity weak because it is acting in more than 4 dimensions?
* What are the extra dimensions and how big are they and how many are there (String theory suggests 11 in our universe - but who knows?)
*Can we make mini-black-holes?

All this in awesome PhD comics animated style below

M&G with the American DoD

I stumbled upon these videos today.

While they are old they are very good.

They start from the basics and make their way through the 'syllabus' and beyond.

This one between 9:35 and 14:35 is excellent for explaining AC induction motors (3, 2 and 1-phase AC):

AC MOTORS AND GENERATORS

These are also good:

DC MOTORS AND GENERATORS

MODULATION (from Prelim Physics)

BTW - Borderlands 2 is AWESOME!!!!!!

 

Yellow is a Creative Colour

VSauce actually has some good stuff mixed into its videos (but sometimes tries to do too much) – this video below a good example (VERY good for Physics 9.4.1 TV’s) – and it shows how yellow IS a creative colour

BUT before you watch – make sure you have the chance to play the game associated with the picture below(the video gives it away without you having the fun of figuring it out)

Some of you may have seen it already but if you haven’t it is an interesting challenge. The picture shows images of eight sets of famous 'objects'– built from Lego in a very minimalist way. The fun is figuring out what they are!

Hence have a go before watching he video (BTW the 6th one is a little obscure – maybe especially so for your generation – and the 5th one is from a VERY obscure/foreign source (I had no idea))

 

& a LOL moment

 

Physics & Chem - Journals Vs Media

Below is what I use for Chemistry re accuracy of scientific data presented in mass-media vs scientific - the general idea is the same for Physics - peer reviewed journal articles focus on factual statements, supported by evidence, reporting of error and uncertainty, all sources referenced, Mass media articles usually have a more speculative, sensationalist? approach with little referencing.

For Physics:
Just browse (I don't expect you to read) the following articles (here) and note the differences between the scientific journal articles (these are preprint versions not the final published article on (1) the 'faster-than-light-neutrinos' (2) the paper that suggests that neutrinos are not 'faster-than-light') and the mass media article.

From Chem:
12.4f - Check out the following files. This one is a peer-reviewed journal article. You do not need to read the whole article but note how all statements are supported by evidence, each claim is annotated with a reference (so the reader can check the accuracy of the information and do further research). Note the impartial/factual style of writing and information presented.
Then read this article from a newspaper on a similar topic. Note the style of writing, the lack of references, sensationalist approach. Also note the use of mixed units (ppm and mg/kg). This should always ring alarm bells. They state that the Australian standard for lead is 250mg/kg. They then make a fuss that the Dior lipstick has 0.21ppm lead. Perhaps you should convert 250mg/kg to ppm. Is there need for worry? Why do you think the journalist conveniently decided to change units in the article? For this skill what can you conclude about the accuracy of scientific data presented in mass-media vs scientific journals?

Flight of the Conchords = Awesome

If you didn't already know how awesome they were - now is the time to find out.

Pure genius.

(If you didn't watch the TV show the first 3-4 min might be a bit weird but stay tuned - it is worth it!)

The Reactions to Know

These are the equations you need in your toolbox to support your answers in the HSC. Some are handy to push for the high marks in extended response questions. Some are VITAL to know (eg 3, 4, 7, 8, 10, 11, 12, 14, 17, 18, 19) to achieve the basics of the course.

If you are having trouble remembering them – try to think of them in context. Eg remember what happened in your fermentation experiment, remember how we decarbonated soft drink, remember how ozone blocks UV rays and why CFC’s decompose ozone etc

 

Click on the images for a larger version.

1) Addition polymerisation  eg PVC

HINT
Show 2n monomers so you can show the repeating structure of the polymer chain. NB the square brackets to signify the repeating unit

2) Polymerisation of glucose to form cellulose
HINTS

1)      If you need help remembering the structure of glucose – let me know – I’ve taken a few people through it and it is (for the most part) working

2)      Every second glucose is inverted.

3)      Being a condensation polymerisation there is a water molecule produced for each link – there is always one less link than monomers (think about why) thus there is always one less water molecule than monomers.

4)      Showing four glucose monomers is ideal to illustrate the above but under time pressure two would suffice as long as you note that every second one is inverted.

3) Addition of bromine water to cyclohexene

HINTS

1)      use the carbon chemistry shorthand – ie don’t bother drawing the C and H atoms

2)      Bromine water is an aqueous solution, but cyclohexene and 1,2-dibromocyclohexane are non-soluble in water so are liquids.

4) Fermentation

HINTS

1)      you *SHOULD*  know that ethanol and carbon dioxide are products, that the glucose needs to be aqueous and yeast is required. We do the experiments (and you learned all about ethanol production) so you don’t need to think about these things – you should just remember.

2)      If you know the products then it is just a simple case of remembering that there are TWO of each product.

3)      This is one of the only reactions involving carbon compounds where you don’t need to use structural equations

 

5) Combustion of an alkanol  eg ethanol

HINTS

1)      For all hydrocarbon combustions – balance carbon, then hydrogen, then oxygen (CHO)

2)      Remember that there is an oxygen in the alkanol so you need one less oxygen than normal (ie one of the reasons why ethanol has such complete combustion)

 

6) Incomplete combustion  eg ethanol
HINTS

1)      The simplest incomplete combustion is where C_(s) is the only product

2)      Use CHO

 

7) Dry cell reactions
HINTS

1)      Never hate mangoes watery monkey nuts

2)      You should know that ammonium has a charge of +1 (it is the ‘t’ in hate)

 

8) Silver cell reactions

HINTS

1)      The silver and zinc reactions are basically opposites of each other

2)      The oxide and hydroxide must be on opposite sides of the equations

3)      Hydroxide is consumed at the anode and produced at the cathode

 

9) Radioactive decay
HINTS

1)      RULE 1 – If Z > 82 = alpha emitter

2)      RULE 2 – If n/p is too high = beta emitter

            Z < 20 : n/p = 1:1

            Z ~ 50 : n/p = 1.3:1

Z ~ 80 : n/p = 1.5:1

Eg 1) C-14

C has 6 protons

Thus there are 14-6 = 8 neutrons

n/p = 1.33:1 – too high s it should be 1:1 – thus it is a beta emitter

Eg 2) Hg-210

Hg has 80 protons

Thus there are 210-80 = 130 neutrons

n/p = 1.625:1 – too high should be 1.5:1 – thus it is a beta emitter

Eg 3) Sn-115

Sn has 50 protons

Thus there are 115-50 = 65 neutrons

n/p = 1.3:1 – just right = stable

Eg 4) At-217

At has 85 protons – thus it is an alpha emitter

 

10) Acid rain

HINT

All you have to show is that it forms an acid – thus if you can show sulphur dioxide forming sulfurous acid or nitrogen dioxide forming its mixture of nitric and nitrous acid you can stop

11) CO₂ solubility

HINTS

1)      Generally, non-polar covalent molecular compounds do not dissolve in water. Carbon dioxide is an exception because it REACTS with water

2)      The reaction is as simple as just adding the atoms of carbon dioxide and water together – remembering to use an equilibrium sign!

 

12) Citric acid
HINTS

1)      Remember that it is the oxygen of the hydroxyl group that bonds to the carbon

2)      Carboxylic acid groups have a double bonded oxygen and a hydroxyl group

 

13) Esterification  eg pentyl ethanoate
HINTS

1)      Remember it is EQUILIBRIUM

2)      Remember that it needs a concentrated sulfuric acid catalyst

3)      Remember that is produces water

4)      Remember that primary alkanols from propanol onward need to end with ‘…an-1-ol’

 

14) Haber equilibrium
HINTS

1)      Know the formula of ammonia

2)      Know that it comes from hydrogen and nitrogen gas

3)      Balance the equation

4)      Know that it is in equilibrium

15) Ozone

HINTS

1)      When writing the ozone equilibrium always show O3 absorbing UV – this is so you can explain how the ozone layer absorbs UV

2)      It is good practise to label the coordinate covalent bond for ozone (distinguishing the electrons from each oxygen is also useful)

 

16) CFC’s decomposing ozone
HINT – to show that it is a catalyst for ozone decomposition you must show them reforming (ie catalysts provide a reaction pathway that lower the activation energy but are not consumed in the reaction).

 

17) Rusting
HINT – if you want to do well in the shipwrecks option you need to know these four equations. They can be used to explain just about everything about the factors that effect rusting and rust protection systems

 

18) Sulfate reducing bacteria
HINT – Soloh ate his two sneakers for water. Need I say more?

 

19) Precipitation
HINTS – This is as simple as I can make the solubility rules for the HSC

1)      All Group 1 metal, ammonium, nitrate, acetate (and phosphate in acidic conditions) compounds are SOLUBLE

2)      All other carbonates and phosphates are INSOLUBLE

3)      Chlorides are soluble except lead and silver

4)      Hydroxides are soluble except lead, silver, iron and copper

5)      Sulfates are soluble except for lead, silver, barium and calcium

6)      Carbonates bubble in acid

7)      Flame tests – barium = apple green, calcium = brick red, copper = emerald green

 

 

Accelerators

Here are some interesting clips of accelerators

1) I couldn't find a good one of a linac - but here is something 'similar'

2) Here are some cyclotron videos - despite the strange voice, the first one is pretty good



3) I couldn't find a good synchrotron clip that was short enough - check here for some previous good CERN videos and if you can stomach it - there is a documentary by Brian Cox about CERN below



4) And here is something that I haven't been able to do in 34 years