Acidity and Basicity in Benzene based compounds

Whilst trawling through your notes you may have noticed a similarity between the explanation why phenol is a little bit acidic and why phenylamine is a little bit basic.

The explanation is effectively the same but the effect it almost the opposite.

Let's first compare the acidity and basicity of their alkyl chained compatriots

• Butanol is neutral, phenol is slightly acidic.

• Butylamine is basic, phenylamine is much less basic

So the presence of a benzene ring as opposed to an alkyl chain makes...

• a hydroxyl functional more acidic 

• an amine functional group less basic 

Before we go any further, remind yourself as to the definitions of an acid and a base.

• Acids are proton donors, so anything that makes a molecule more likely to give away a proton makes it more acidic. 

• Bases are proton acceptors, and to do this they need a lone pair, so anything that makes a molecule less likely to accept a proton would make it less basic.

So. let's answer the questions

• Why is phenol acidic when butanol isn't?

          and

• Why is phenylamine less basic than butylamine?

The answer to both questions comes down to the lone pairs.

If an atom with a lone pair on it is attached to a benzene ring then this lone pair becomes part of benzene's delocalised system. This delocalisation means the negative charge doesn't just sit there on the atom, it moves around the molecule. This fact can be used to explain both the questions above.

So, to explain phenol's slight acidity (compared to butanol's neutrality)...

Phenol is acidic because the phenoxide ion formed is stabilised to some extent. The negative charge on the oxygen atom is delocalised around the ring. The more stable the ion is, the more likely it is to form. So Phenol is acidic because the ring draws the lone pair away from the ion

and, to explain phenylamine's reduced alkalinity (compared to butylamine's alkalinity)...

Phenylamine is not that basic because the lone pair is no longer fully available to join to hydrogen ions. Nitrogen is still the most electronegative atom in the molecule so the lone pairs of electrons will still be attracted towards it, but the intensity of charge around the nitrogen is nothing like what it is in butylamine. So phenylamine is a not so good base because the ring draws the lone pair away from the nitrogen.

Notice how the two diagrams are almost identical

Make sense? 

Two effects, one reason.

Azo-Dyes

What is there to say on this self contained little topic.

If you have a benzene interconversion map you should have it all on there.

Here is a little summary of the topic just to make sure you know what is going on.

I am not going to go through the pathway from benzene to benzenediazonium chloride.. .oh, OK then I will

1. Benzene with Conc H2SO4 and Conc HNO3 (at about 50C) makes Nitrobenzene
2. Nitrobenzene with Tin and Conc HCl makes Phenylamine
3. Phenylamine with Sodium Nitrite and Conc HCl - Nitrous Acid (below 5C) makes Benzenediazonium chloride

Happy now?

This is benzenediazonium chloride

Benzenediazonium chloride and nitrous acid are unstable above 5C so you have to keep it cool when this stuff is around.

If you let things get a bit hot you get phenol and some bubbles of nitrogen gas given off (that sounds like a test to me).

Benzenediazonium chloride can be added to loads of molecules with benzene rings to make dyes. The three examples you need to know are with...

1. Phenol

2. Napthalen-2-ol

3. Phenylamine

Pretty repetitive really.

The only relatively interesting thing to point out her is why the O- on napthalen-2-ol and phenol (as opposed to -OH. This is explained by the condition needed which is in NaOH (i.e. alkaline conditions). All acids lose their proton in alkaline conditions and as both of these phenolic groups are alkaline then  - protons begone!

These two benzene rings linked by a N=N are a chromophore so all of these molecules are dyes. 

You don't need to be able to name them as they have several possible names, just remember the formula.

OK, enough chemistry for me for one evening it's back to the mince pies and TV.

Reaction Types - Fool Proof Guide

Ever wondered how to work out which reaction are electrophilic, nucleophilic, substitutions, additions?

There is a fairly fool proof way to work it out.

Electrophilic - This needs electrons to be attacked. So will happen to benzene (cloud of them), alkenes (double bond full of them)

Nucleophilic - This needs a very electronegative element to pull the electrons away and create a delta positive carbon - so alcohols, aldehydes/ketones, halogenoalkanes are the main culprits.

Addition - If you are going to add on an extra atom you need some space to add some extra bonds, (i.e a double bond) so that means alkenes with almost anything (electrophilic) and aldehydes and ketones with HCN (nucleophilic)

Substitution - There are two reasons why you would get substitution reactions...

1. The molecule is stable as it is and adding anything would disrupt that stability (i.e. benzene)
2. The carbon being attacked doesn't have space for extra atoms so if something is coming in,
    something else has to leave  - like a one in one out policy (i.e. alcohols, halogenoalkanes).

There we have it. Four different types of reactions. A (relatively) fool proof way to tell them apart.

99 Uses for Sodium hydroxide ( or why is it just So-dium useful)

You may have noticed as you travel through the world of organic chemistry with just a tattered A3 map to guide you that many of the paths are marked with sodium hydroxide. So, here is a quick summary of all the uses of NaOH...

1. As a Base
Fairly obviously NaOH is a base, so any time it comes across an acid it neutralises it (as you learnt circa 2008).

The only two acidic functional groups you will come across in CH4 are phenols and carboxylic acids. In both case you will get the salt formed. Either sodium phenoxide or a sodium carboxylate salt (ethanoate, propanoate etc.)

2. As molecular scissors (i.e. base hydrolysis)
Sodium hydroxide is also used in two different places break molecules in half.

Esters and amides (N-substituted or otherwise) are both hydrolysed by NaOH. In both cases you get a carboxylate salt (remember the fact about making carboxylic acids in alkaline conditions - you always get the salt).

This carboxylate salt can then be converted back to the carboxylic acid just by adding a sprinkling of aq H+.

A fact worth remembering here is that the condensation polymers, polyESTERS and polyAMIDES and proteins can be hydrolysed by NaOH like this as they have loads of amide/ester functional groups.

3. For decarboxylation
In all the other reactions so far, the NaOH has been aqueous. In fact NaOH is prety much always aqueous as "conc" NaOH is solid and will absorb the water from the air, turning your solid NaOH into a corrosive mush. For this reaction we need to keep the NaOH solid so we add calcium oxide to it. This prevents it absorbing the water from the air and we call this mixture of NaOH and CaO, soda lime. Strong heat is needed here so don't forget to mention it. You need to know this symbol equation so please remember it.

So, if you are asked for the reagent you write soda lime, If you are doing a symbol equation you write NaOH (or OH-) as the active ingredient in soda lime is NaOH. The CaO is the chemical equivalent of packaging.

Other points to note here are that CO2 gas is not made in the reaction, as even though CO2 is removed from the molecule it goes straight into a molecule of Na2CO3.

Also, worth noting is that the carboxylic acid or carboxylate salt being decarboxylated must be solid. This isn't a problem for the carboxylate salt as all salts are solid (it's that ionic bonding they can do). Carboxylic acids tend not be solid until the chains get really long so you would need add a bit of aq. NaOH first to the carboxylic acid, evaporate off the water to make the solid salt of the carboxylic acid( not the carboxylic acid itself). I wouldn't stress about this point too much though as it doesn't really come up in the exam.


4. To do some nucleophilic substitution (Halogenoalkane to Alcohol)

Finally, this is a straightforward substitution where the halogen is removed to be replaced by an OH. magically transforming this molecule into an alcohol. A bit of heat under reflux is required to get this going other than that there is not much else to say.


If I have missed any reactions please let me know an I will create an addendum to this post.

P.S. There is nothing special about sodium hydroxide in all cases potassium hydroxide, calcium hydroxide etc.would do exactly the same. It's just that in a lab, it is generally sodium hydroxide you have hanging around.

10 Top Tips for an Interview

At some point in the next few months lots of you are going to be going to interviews at University or for jobs. Well, I thought it about time I put in one place my ten top tips for getting through that interview. So, here we go...

1.  Expect the obvious questions - Why do you want to do...? Why do you want to study here? Expect a question on your practical expertise and your subject knowledge in both of these questions. They have to be open ended as all students have different experiences. So when they ask you something like "What are you studying at the moment?" or "Talk about a practical you have done that you really enjoyed". Make sure that whichever answer you give you can expand on it. Don't take them down an alley that you realise you know nothing about. So prepare to talk about a study topic and a prac and be prepared to talk about it. 

2. Research the interviewer - If you know who is interviewing you find out what they are into and read up about that so you can ask some knowledgeable questions of them. There is nothing an interviewer likes more than talking about his own pet subject so google them and find out what they do and find out a little bit about it.

3. Relax - The last thing you want to do is to clam up and say nothing, So try and relax, be yourself and show them how good you can be.

4. Don't relax too much - Don't forget you are being assessed from the moment you step in through the door so don't relax too much and let slip to someone that you don't like this Uni and it is only your fifth choice anyway (in case that person happens to be in on an interview later). Look interested (although not scarily so - don't come across as a psycho) on all the tours and ask questions when given a chance. 

Also, curb the attempts at humour, when the interviewer says "Please, take seat" the response "Where shall I take it?" is not going to go down well, they are looking for a student not a stand up act. Be funny, if appropriate, but err, on the side of, this is not a time for one liners.

5. Read the newspapers - Find out what is in the news for your subject area, nothing worse than knowing nothing about a big story in the news.

6. Think about what they are looking for (and what they are not) -  Think of the five things you think they are looking for in a student and think about how you are going to get across those attributes on the day. Also, think about the worst attributes of a student (especially the ones you know you can be guilty of) and try your best not to demonstrate them. e.g. avoid stories about getting so drunk you missed a whole morning of lessons or how once you forgot your homework so copied your friends. This may sound obvious but I have heard people do it when they relax during coffee with some of the team doing the interviewing.

7. Dress appropriately - Everybody has their own style but now is not the time to show them your most outlandish outfit. Read what they say in the letter (formal? smart casual?). If they don't say anything, be conservative and go in what you consider smart but not over the top. Shirt, trousers (no trainers, football tops or jeans) does the job for blokes, smart skirt or trousers and a top (again no trainers, denim or anything too "Saturday night in Mold"!) for the ladies.

8. Don't be late - If you are travelling a long way consider staying overnight the night before, gbet there with plenty of time to park, find your way in and have a look around. Don't run in 10 mins late with a heart of 120BPM, sweating and making excuses about the traffic or train punctuality. 

9. Do you want the place? - These interviews are often about you finding out about them as well as them finding out about you, so give it some though, can you see yourself there?

10. Make a good first impression - There is a psychological fact along the lines of "...most interviewers decide who they in the first 5 seconds of meeting them". So don't shuffle into a room, staring at your feet, with your hands in your pockets. 

Walk tall, be calm and be the person they want at their Uni. If they decide you aren't that person it's their loss.

Good Luck.

Zooniverse

If you have never tried this before, have a look here , it is fantastic. 

The principle of the project is that there is loads and loads of scientific research going on out out there but not enough people to analyse the data.

So, why not set up a website that allows people to analyse the data from the comfort of their own computer screen? 

Great idea and that's exactly what Zooniverse is.

The range of projects is amazing and includes...

Explore the surface of the Moon - We hope to study the lunar surface in unprecedented detail.

Go wild in the Serengeti! - We need your help to classify all the different animals caught in millions of camera trap images.

Analyse real life cancer data. - You can help scientists from the world's largest cancer research institution find cures for cancer.

How do stars form? - We're asking you to help us find and draw circles on infrared image data from the Spitzer Space Telescope.

Hear Whales communicate - You can help marine researchers understand what whales are saying

What I love about this is that this is REAL SCIENCE! It isn't a made up scenario for the purposes of education this will really help scientists all over the world in their research and at the same time give you an insight at what is going on in the world of science.

So get off Candy Crush/Farmville/WoW/CoD and go and cure cancer/Listen to some Whales/Explore the Universe/Save some Zebras.

One world is real, the other is make believe. Which is it worth spending most  time in?

Career in politics anyone?

In the reshuffle of the ministers of the Welsh Government announced today. There was a significant coincidence in amongst all the other flannel. The new Minister for Education and Skills is an ex-Chemistry teacher (Huw Lewis AM) and the new Deputy Minister for Skills and Technology is an ex-Alun School pupil (Ken Skates AM)

If you don't believe me, here are the links to the news stories

Huw Lewis is named Wales education minister
Ken Skates Biography on Welsh Government website

I guess it is a career option we can all fall back on if things don't work out for us.

See you all in government

Amphoteric Behaviour and Aluminium

OK, Aluminium ions are amphoteric. Which basically tells you that they will react with acids and bases. The question is though if that is true, how can this be proved using just one chemical (sodium hydroxide). Right lets think this through

Think of aluminium Nitrate. The aluminium ion is the amphoteric bit (not the nitrate).


So, if you start with aluminium nitrate it will turn into aluminium hydroxide (white ppt)

like this...

Al3+  +  3OH-  --> Al(OH)3(s)

Now at this point the aluminium hydroxide could do the obvious thing of behaving like a base and reacting with some acid to make salt and water

e.g.

Al(OH)3  +  HCl  --> AlCl3  +  3H2O

or (and this is the super important/exciting amphoteric bit)

it could react with NaOH and become Al(OH)6 3-

Al(OH)3  +  3OH-  --> Al(OH)6 3-

So adding more OH- proves it is amphoteric because it proves it can do both things.

Any old hydroxide salt can react with an acid but only magic amphoteric ones can react with bases as well

NOTE - Amphoteric compounds aren't magic

Aspirin giving you a headache?

What do you need to know about aspirin?

Almost nothing. Isn't that what you wanted to here.

Aspirin production was in the old spec but has almost completely gone from the new spec. So you will find questions in the old spec CH4 questions about it.

The only thing you need to know is that making aspirin is one of the uses of acid anhydrides.

So remember that fact, laugh in the face of the aspirin based questions and move on.You will feel much better for it

Special Agent (or why is Manganate sometimes used acidified and sometimes in alkaline solution)

Potassium Manganate (VII) is either used acidified (when oxidising alcohols) or in alkaline solution (when oxidising methyl benzene)

The reason why you have to acidify the manganate VII for the oxidation of alcohols is because the reaction needs H+ to combine to make water from MnO4-'s oxygens. As you saw in CH5 when doing redox half equations for Manganate (VII).

The reason why you need alkaline conditions when oxidising methyl benzene - I have no idea. 

I even googled it and found some degree level notes on it and they said the mechanism was to complicated to explain at degree level. So if I was you, I would assume it is wizardry and move on.

Sounds a Bit Fishy (or Naming N-Substituted Amides - CH4)

N-substituted amides are named in two parts (a bit like esters). So lets look at an example

N-methyl ethanamide

If you look at the molecule, it is an ethanamide with a methyl hanging off the Nitrogen

The ethanamide is on the left (with the amide functional group in the middle) and the methyl is hanging off the N of the amide link (hence N-methyl)

If you remember that the chain that is attached to the N is the one which is the "N-...." at the start of the name then that will tell you which chain goes where.

What about working it out from the reactants (i.e. amine and acyl chlorides)

The amine brings in the N so the amine chain will the N-... chain

and the acyl chloride brings in the rest.

TO be honest this rarely come up in CH4 so I wouldn't worry too much about it!

Is it just me or does Rumpelstiltskin look like the hazard symbol for an oxidising agent? (CH5)

Rumpelstitskin                             Oxidising Agent Hazard Symbol

Anyway, back to the science, the best oxidising agent has the most positive standard electrode potential

e.g. Iodine will oxidise anything that is a worse oxidising agent than it. Which is all those with a value of less positive than +0.54v.

When deciding whether things will oxidise things you must compare oxidising capabilities. If you turn the value around you are not comparing like with like. You would effectively be comparing oxidising ability with reducing ability, which makes no sense.

So when deciding what different elements can oxidise look at the values as stated, as the values show the strength of the species as an oxidising agent.

If the question is "What can this species oxidise?"the answer is the name of the more reduced species e.g. Cu, Ni and Fe not Cu2+, Ni2+ or Fe 2+ as that is what would be oxidised.

To finish, a top Shrek quote...

Gingerbread Man: Okay, I'll tell you... Do you know... the Muffin Man?
Lord Farquaad: The Muffin Man?
Gingerbread Man: The Muffin Man.
Lord Farquaad: Yes, I know the Muffin Man. W-who lives down on Drury Lane?
Gingerbread Man: Well, she's married to the Muffin Man...
Lord Farquaad: The Muffin Man?
Gingerbread Man: THE MUFFIN MAN!
Lord Farquaad: She's married to the Muffin Man...

Why aren't all crystal lattices 6:6 or 8:8?

Lets start off with a reminder why NaCl is 6:6 and compare thaty to CaCl2

The NaCl the structure is 6:6 because in that lattice the structure the ions take up is controlled by the size of the smaller Na+ ion and how many Cl- ions you can fit around it, (i .e. Na+ is small so you can only get 6 Cl- around the Na+).

The other number 6 (in 6:6) comes from the fact that to maintain the 1:1 ratio that NaCl must have, you need 6 Na+ around each Cl- too. You could get a lot more Na+ around the Cl- but that would spoil the 1:1 ratio.

(Why must NaCl be 1:1?

Sodium has 1 electron in the outer, which it needs to lose to form a stable ion. Chlorine needs to gain one to from a stable ion. So 1 sodium needs to lose 1 electron to 1 chlorine to be stable. Happy Days.)

Now, lets apply the same logic to CaCl2. Whatever structure CaCl2 takes, it must maintain the 1:2 ratio (for the same reason as above).

The 6:6 structure maintains a 1:1 ratio so it would never work for CaCl2.

You don't need to know the structure CaCl2 takes, all you need to know is, it is not 1:1, so can't be 6:6 (i.e. the same as NaCl.)

"Health and Safety" gone mad

Just to cheer you up if you are revising hard.

If you are not revising hard, get to it.

Dinosaurs didn't revise and they are extinct.

Correlation or Causation?

Bonding Types - What is that all about?

Answering bonding questions in CH2 is a really big problem. How do you know which bonding type a molecule has? How do you describe it? Here is a quick guide to enable you to at least start to answer these questions.

Lets think through first what type of bonds the molecule has.

If it has ONLY METAL atoms it has ONLY METALLIC bonds. Metallic is fairly straight forward higher charged ions = stronger attraction to electrons = higher BP/MP. Easy.

If it has METAL AND NON-METAL atoms it has ONLY IONIC bonds. Again straightforward you need to know your CsCl and NaCl stuff here and the forces of attraction and repulsion. Not too tricky.

If it has ONLY NON-METAL atoms it has COVALENT bonds IN the molecule and one/two or all three of the INTERMOLECULAR forces BETWEEN the molecules. Now this is the one that trips people up.

There are so many possible molecules here that you can't learn them but you can work out which sort of bonds they have.

Before I start there is a difference between what bonds a molecule has and which ones are important, for example water can do ID-ID but they are not important because the hydrogen bonds are so much stronger that only they matter. So here are the intermolecular bond types in order of importance from least to most.

1. Instantaneous Dipole-Induced Dipole (ID-ID)

If a molecule has...
...only one sort of atom (e.g. Cl2)
...all the same sort of atom on the outside (e.g. CH4)

...then the only sort of intermolecular force it can do is Instantaneous Dipole-Induced Dipole (ID-ID). This happens because all the electrons are swishing around and creating temporarily positive/negative ends of the molecule that then attract other molecules. As molecules/atoms get bigger there are more electrons and therefore stronger ID-ID, therefore, higher BP/MP. All molecules that have covalent in the molecule will have ID-ID between molecules but they are only important when the molecule can't do the other two types of force.

Don't forget then that all covalently bonded simple molecules can do this bond it is just that it only becomes important when it is the only bond that they can form (i.e. in non-polar molecules)


2. Dipole-Dipole (D-D)

If a molecule has a permanently positive and a permanently negative end then that molecule has a dipole, in other words it can attract molecules/atoms/ions of the opposite charge towards it...permanently. It is like the one above but it doesn't change. More electrons don't make a difference now because it is not down to swishing of gangs of electrons. This bond just gets stronger when dipoles get bigger because electronegativity differences become bigger.

On this one just be careful with shapes, e.g. NH3 might look non-polar because it has all the same type of atom on the outside but it is polar. When you look at the shape it is trigonal pyramidal with the N at the top point and all 3 Hs at the other three points.  So there is a negative end (the N) and 3  positive ends (the Hs) so it will do D-D (as it happens it will also hydrogen bond but that is a different story)

3. Hydrogen Bonding

This is the strongest of the three. This is a special case. IN THE MOLECULE, you need to have a very electronegative atom with an active lone pair directly attached to a hydrogen, i.e. in the molecule there must either be a H-F,H-O or H-N bond.

The bond will then be formed between the N, O or F of one molecule and the H of the other.

Your obvious examples of molecules that can Hydrogen bond are water, ammonia and HF but there are lots of other.

If you want a quick summary, here goes

Metal atoms only - Metallic

Metal and Non-Metal atoms - Ionic

Non-Metal atoms - Covalent IN the molecule and then BETWEEN the molecules...

Non-Polar molecules - only ID-ID
Polar molecules - D-D and ID-ID
A molecule that has N-H, O-H or F-H bonds - ID-ID, D-D and hydrogen bonds

(I have emboldened the one that matters in that last statement)

Simple? Not really that hard once you get your head around it.
Worth understanding and working on? Definitely as it is guaranteed to come up in CH2.

Q - When is a triangle not a triangle?

A - When it's a pyramid
There are two molecular shapes that could be described as triangular (or trigonal). One is a...errr...a triangle and it is referred to as trigonal planar. The other is effectively a triangular based pyramid, called equally obviously, trigonal pyramidal. The reasons behind the differences in the two are important.

Trigonal planar is flat (i.e planar) so imagine a triangle with three atoms at each corner and one in the middle. Each of the corner atoms are 120degrees apart (i.e. 360/3 = 120). You get trigonal planar when you have three bonded pairs and no lone pairs as that is the furthest the electron pairs can get away from each other. an example is BF3

Trigonal pyramidal is like...erm... a pyramid but a pyramid with a trigonal base (hence the name). The bond angles are 107degrees (no way of working that out you just have to remember). You get trigonal pyramidal when you have 3 bonded pairs and 1 lone pair. The lone pair is more repulsive and pushes the bonded pairs down and  away from being trigonal planar (which is what you would get if the lone pair wasn't there). An example is NH3

P.S. The purple lump on the trigonal pyramidal isn't a comedy hat it is a lone pair of electrons.

Oxidising Agents and Reducing Agents

OK, you have two chemicals, one is being oxidisied (losing electrons) and the other is being reduced (gaining electrons). Both must be happening at the same time. Otherwise where are the electrons going? If you want an analogy, there is no thief that has no victim and no victim of theft without a thief.

So, the species being reduced is always being an oxidising agent (it is causing the other thing to be oxidised) and the species being oxidised is always being a reducing agent (it is causing the other thing to be reduced), No exceptions. 

Does it matter whose fault it is? Does it matter that one species really wanted to gain an electron while the other was fairly ambivalent whether it lost one or not? Conversely, does it matter that one species really wanted to give one away and the other species that happened to be passing was just a willing recipient?

Quite frankly, no. It doesn't matter whether it really wants to or no, the species that loses the electron, causes the other to gain so is a reducing agent and the species that gains the electron caused the other one to lose an electron so is an oxidising agent.

There is no blame game where it comes to redox they are all agents.

Why are bonds different lengths?

(above) Not a bond

It must have crossed your minds at some point why are some bonds longer than others. Why is a hydrogen bond long, a covalent bond short and a double covalent bond shorter still. 

The answer is simple.

Bonds aren't physical things like pieces of string they are just attractions. The stronger the attraction the shorter the bond. So, simply covalent bonds are stronger than hydrogen bonds so they are shorter. 

Why do you get that 180 bond angle between water molecules?

Right this is difficult to explain without a board pen and some pointing but here we go.  

The 180 degrees I am referring to here is for the H that is covalently bonded to an O on one side and Hydrogen bonded to an O on the other (see picture). 

This hydrogen has a covalent bond on one side (i.e. a bonded pair) and a hydrogen bond on the other. Now, technically the hydrogen bond is not a bonded pair of electrons but the oxygen that the hydrogen is hydrogen bonded to is a big ball of negativity (imagine a fat dementor) that behaves much like having a pair of electrons on that side too. So effectively that hydrogen has 2 bonded pairs, and what shape do molecules with 2 bonded pairs take...straight line. 

So there we go, that is your answer. The actual answer in the exam goes along the lines of...

"...because it has two bonded pairs of electrons and to take the position of minimal repulsion the electron pairs  get as far away from each other as possible which is a straight line."

What's HOT and What's NOT in the world of Chemistry (or Spot the Difference)

Whenever they change specification (like they did 4 years ago) they always take some stuff out and put other new stuff in. 

There is no good reason why, except to confuse pupils and teachers . So, those of you doing the old specification papers will be very confused from time to time when they ask a question that looks like it is written in greek because you don't recognise the stuff at all or you didn't think you needed to know in that level of detail.
So, to help you through, here is a list of all the changes that come to mind. I may have missed something, so please point in out if there is something else that you think is different.

AS
New In!
Hydrogen Emmission Spectrum
Smart Materials
Carbon Nanotubes
Nanotechnology
Green Chemistry

Gone!
Electron Density Distribution

Equilibrium Constants (now in A2)

A2 

New In!

Hydrogen Fuel Cell

Group 3

Chromatography

Gone!

Group 1 and 2

Hydrogen Emission Spectrum (now in AS)

Testing, Testing, 1, 2, 3... (CH4/CH2)

One of the hardest aspects of organic chemistry is remembering all the wet tests that you need to carry out to differentiate between different functional groups that you are likely to come across. 

Not only do you have to remember the compounds that give a positive (and the ones that don't), you need to  remember the observations, the chemicals you need to add to get this thing to work and some seemingly random facts that someone deemed important. 

To help you through this, here is a list of all the tests you are likely to come across and an attempt at the relevant detail. I have also indicated whether these are relevant for CH2 or CH4

Tollen's Reagent (CH4), Fehling's Reagent (CH4), Acidified Dichromate (CH4 and CH2)
These three are collectively known (by me at least) as the oxidation tests, each depends on a molecule being oxidised. So molecules that are easily oxidised give a postive, namely aldehydes, primary alcohols and secondary alcohols. 

The only thing that changes is the observation.

So for Tollen's Reagent you see a silver mirror (or more likely if your test tubes could do with a wash - a grey ppt)

For Fehling's Reagent you see a orangey brown ppt

For Acidified Dichromate you see the orange solution go green

Other facts worth remembering are...

• Tollen's reagent is fairly rubbish as an oxiding agent so it is not strong enough to work with primary alcohols (such as ethanol)
• Fehling's is almost the same Benedicts solution (remember from biology, the test for reducing sugars)

Iodoform Test (CH4)

Iodoform (or triiodomethane or CHI3) is the name of the test but in this case it is not the name of the reagent you add. In fact, Iodoform is the yellow stuff you see at the end that tells you the test has worked. 

The reagent you add is aqueous alkaline iodine (or iodine, mixed with aqueous sodium hydroxide) it also works with Potassium Iodide and Sodium Chlorate (I), You generally don't need to warm it but if its being a bit slow a bit of heat helps.

The observation is a yellow ppt (of Iodoform) that smells of ...erm...Iodoform which is basically an antiseptic smell, which makes sense as iodoform used to be used as antiseptic.

People often come unstuck in what gives a positive. Positives are given by methyl ketones or methyl hydroxyls. That is -OH or C=O groups being on the carbon next to a CH3. For example -  ethanal, ethanol, propan-1-ol, Propanone  all give positives but methanol, propanal and pentan-3-one all give negatives. Think this one through, draw the molecules and try and work it out, if you are still stuck have a look here. 

2,4 DNPH (CH4)

Nice and easy one this one. Positives are given by aldehydes and ketones and it looks like a bright orange ppt. The only other factoid that they want you to know here is that this is an example of an addition-elimination reaction. Don't bother learning the mechanism just remember that fact.

Lucas Test (CH4)

This is technically not in the syllabus so they can't ask a question where this is the only answer and it won't be in the mark scheme as a possible answer but it does work and could get you out of jail if you don't know the actual answer but if you can don't use this as your answer of choice as it won't be in the mark scheme and a half asleep examiner may well mark it wrong if they aren't concentrating.

Anyway (briefly), what is it? Reagent is Conc Hydrochloric Acid and Anhydrous Zinc Chloride. Tertiary Alcohols give a white ppt v quickly, secondary alcohols give a white ppt v slowly. Primary Alcohols don't give a white ppt but neither does anything else so that fact doesn't help you much.

Sodium Carbonate Test (CH2 and CH4)

Simple idea this, acids bubble with metal carbonates. So if you add sodium carbonate solution to any acid (including carboxylic acids) you will get bubbles that turn lime water milky. 

Tests for Phenol (CH4)

Two of these, either... 

•  add Iron (III) Chloride and the solution goes purple

            or

• add bromine water and it decolourises and you get a white ppt

Enough said, lets move on.

Test for Alkenes (CH2 and CH4)

This is an easy one you should all know from GCSE. Alkenes decolourise bromine water. In other words it goes from being a browny-orange colour to being colourless (NOT CLEAR!!!)

Test for Amines (CH4)

This is a spin off from all that di-azo stuff that you do. When you add nitrous acid to an amine it forms a di-azo compound that is really unstable so it immediately breaks down to give off bubbles of nitrogen gas

Test for Amides (CH4)

Again this is a consequence of a conversion reaction. When you sodium hydroxide to an amide and heat it a bit it gives off ammonia. You will know because it stinks but if your nose isn't working then test it with damp red litmus paper and it will go blue. The only possible confusion here is with ammonium salts which also give off ammonia with sodium hydroxide but that will happen in the cold, so it is usually possible to tell the difference.

Test for Halogenoalkanes (CH4 and CH2)

Halogenoalkanes are known for being unreactive so the only way to test for them is to chop a bit off and test that. So, add some sodium hydroxide, this will then release the halide ion. 

The halide ion can then be tested for by adding a mixture of silver nitrate and nitric acid (the acid is just there to neutralise any excess sodium hydroxide from earlier).

The observation will depend on the halide ion - so white ppt means chloride (so it was a chloroalkane) cream ppt means bromide (so it was a bromooalkane) and yellow ppt means iodide (so it was an iodoalkane).

There we have it all the test in one place. If I have missed anything please leave a comment and I will add it. 

Y12 if you are getting stressed by the 4 you have to learn for CH2 spare a thought for Y13 who had to learn all of these others for CH4, as will all of you next year...  

pH Curves in 60 seconds

pH curves are inherently hard things to get your head around but once you do getting it is very worthwhile, so here is my 1 minute guide to what working them out...

1. Shape - Think of each curve as made up of 2 half curves and there are 4 possible half curves (weak acid, strong acid, strong base, weak base), the shapes will either be almost L shaped (Strong) or almost fallen over S shaped (weak) and either high (base) or low (acid). So, when drawing (or describing) a curve just think, what is in the conical flask before I started titrating and draw the half curve for that first, then think what am I adding to it from the burette and draw that sort of half curve next.
2. Intial pH - is the pH in the conical flask before you added anything
3. Estimate of final pH - this will be very close to the pH of whatever was in the burette but reduced a bit (if its a base) or increased (if its an acid)
4. Equivalence volume - Volume it gets v steep
5. Equivalence pH - Middle of v steep section
6. Getting Ka from graph - At 1/2 equivalence volume the Ka = H+ (or pKa = pH)
7. Where is there a buffering effect? - If you have a weak acid or a weak base, in the middle of the half curve for this solution the curve flattens for a bit, this is the buffering effect, this happens because there is a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid)

59, 60. Done

Naming Multifunctional Organic Molecules

If you are naming molecules with multiple functional groups your first priority is to keep the numbers low and then when you write the name you put them in alphabetic order.

So for example this molecule...

...is called,  3-Chloro-1-Iodo butane

This is right because

- it keeps the numbers low (the alternative is "2-chloro-4-Iodo", i.e. 1,3 is lower than 2,4)

- and we have put it in alphabetic order

There is a more complicated rule that groups have different priority based on their Mr but you don't really need to know that,

The other fact it is worth knowing is that if you have a functional group that must be on the end, mainly aldehydes and carboxylic acids, you wouldn't number these because they have to be on the end (obvs) but then when you put other functional groups on you can't start numbering these "end only" functional groups because that would make no sense, it which case you always assume that the "end only" functional group is at 1 and number from there and this overrides the rule about keeping the numbers low.

So for example... 

...is called, 4-Chloro-3-Methyl Butanoic Acid

NOT

1-Chloro-2-Methyl Butan-4-oic Acid

Even though the numbers are kept lower on the alternative name.

The only other thing worth remembering is that of you have more than one of a functional group it becomes, for example, 1,3-dimethyl or 1,3,3-trimethyl and then when you are alphabetising them you go by the "d" or "t" not "m" e.g. it would be "1,3-dimethyl-4-ethyl....." not "4-ethyl-1,3-dimethyl-....."

Isn't It Ionic?

Ionic or Covalent? What is electronegativity?

This is a fairly confusing area of A level Chemistry (Alanis Morissette certainly found it hard) so I thought I would put together a blog post to explain it.

Think of it this way, we need to measure the ability of atoms to draw electrons towards them (i.e. electronegativity) the only way of doing this is on a comparative scale, that is, compared to other atoms. Then all somebody did (the man who did it was called Linus Pauling) was to give this scale values. The reactivity series from GCSE is the same principle except that nobody has ever bothered to give reactivities values so it is still just a list.

Anyhow, if you are going to compare atoms electronegativity (and therefore assign values) you need to get in to a situation where two atoms are both trying to pull electrons towards them and see which one has the bigger pull.

The only place this happens is in a covalent bond. In a covalent bond the electrons are shared between the two atoms but the electrons will spend more time with the atom that has the greater pull and therefore we say that atom is more electronegative (than the other one it is bonded to).

So, by comparing the covalent bonds between every possible pair of atoms you get a hierarchy of pulling ability (electronegativity) which Linus Pauling assigned numbers to. On Pauling's scale, Fluorine is the highest (best at pulling electrons) and is assigned a value of 4.0 and Francium is the lowest (poorest at pulling electrons) at 0.7. All of this measurement is done by comparing pulling ability in covalent bonds.

So the definition has to be something along the lines of...

"Electronegativity is a chemical property that describes the tendency of an atom to attract electrons towards itself in a covalent bond".

So, "How can compounds that form ionic bonds have electronegativities?" I hear you ask.

Electronegativity is a property of an element, if the value is high (e.g. Chlorine, 3.2) the element will form covalent bonds with other atoms of high electronegativity, because they are both pulling really hard on the electrons and so end up sharing them, but will form ionic bonds with atoms of low electronegativity (e.g. Na, 0.9) because the chlorine has so much of a bigger pull on the electrons compared to the sodium that it ends up pulling the electrons towards itself completely and forming a negative ion, whilst the sodium loses its electron and ends up being a positive ion.

So, don't think of electronegativity as happening "in bonds". It is a property that controls what sort of bonds an atom will form.

The only loose end to tie up is how do we know sodium's electronegativity if it never forms covalent bonds (pure sodium forms metallic bonds and sodium compounds have ionic bonds). The answer to this is that even though sodium doesn't naturally form covalent bonds, in a lab it can be made to share electrons (i.e. form a covalent bonds) with other atoms so that its electronegativity can be measured.

My analogy for all this is tug of war competitions, I won't expand on it now but it does work pretty well.

....and in future Alanis, just buy less spoons.

Bad Science - 2 - D:Ream, Things Can Only Get Better

"Things can only get better 

Can only get, can only get 

They get on from here 

You know, I know that 

Things can only get better"

D:ream, Things Can Only Get Better

In 1994, D:ream sang that "Things can only get better...", this is excusable as a catchy line in a pop song but in their midst was the man who would later become the high priest of physics - Dr Brian Cox.

As Dr Brian well knew things can, quite literally, only get worse. Due to a thing called entropy, given the symbol, S.

Entropy is a measure of the disorder of a system and for any closed system, the higher the entropy the higher the disorder. 

So for a closed system like the universe, total entropy must always increase, in other words, disorder can only increase, so things can only get worse.

Did the D:ream lead singer know any better? Did the D:ream lead singer care? I suspect not, after all, this was his one shot fame.

On the other hand Dr Brian, the beautiful smiling face of popular science, definitely knew better but as he was consigned to plonking away at the keyboards in the background (he is barely visible in the video above; and if you look at the picture below, it is not hard to see why the camera didn't focus in on him, he is on the far right) I suspect he didn't really have a say in it.

Brian Cox (far right) then... 

                                                    

  ....and now

So Brian, things don't get better, they invariably get worse, except for haircuts, which do appear to have improved over time.