An attempt at passing AS chemistry @attemptingtopassaschemistry - Tumblr Blog

Dear anon,

I haven't been on this blog for what more than a year now? I don't do chemistry at A2 but it seems people are somehow still finding it? Which is pretty incredible! To the beautiful lovely anon who submitted, you made my day. I had an exam today and I have an exam the day after tomorrow and next week, but that message, that message, made it more okay :') I'm glad that it's still useful and that people appreciate what I wrote all those months ago when I was a little AS struggling with chemistry haha! :3

#dear anon

You're adorable..!

I just love going through your tumblr. It's so filled with love - ah such a break from icy cold people around us. Every single sentence you write lightens me up! Just loads of luck and best wishes for you <3 I hope - I know you've a really great bright future ahead.That's all I have to say. Thank you so much. Like seriously! I love you. YOU'RE BEAUTIFUL RUTHIE. Know it please. :)

Good luck to anyone out there who's doing the AQA Chem 2 exam today. *Hugs* I hope you all do really well :) I will be telepathically thinking of all the other people out there, who are attempting to do the questions, and then I won't feel so alone in this.

#chemistry #aqa #exam

A summary of mechanisms

Haloalkanes:

You've got two possible ones:

haloalkane --> alcohol + leaving group NUCLEOPHILIC SUBSTITUTION

haloalkane --> alkene + water ELIMINATION

See the conditions for these reactions here.

Alkenes:

alkene --> haloalkane + leaving group ELECTROPHILIC ADDITION

And here are the mechanisms drawn out:

Nucleophilic Substitution:

The nucleophile is attracted to THE CARBON ATOM and kicks off the halogen group.

Elimination:

This one reminds me of frog leaping because there's so many arrows to remember. The trick is to know it forms WATER and how the water got there. This time the nucleophile is attracted to the HYDROGEN (Say this in a somerset farmer accent - hydrogen is in water and there aint no carbon in water so you dont go choosing that carbon). Also remember it attacks the hydrogen on the "one next to it" not on the one directly opposite the halogen. Think about how the double bond got there. It needs electrons from the C-H bond. And the halogen is kicked off just like normal.

Electrophilic Addition:

This one just remember you've got the carbocation, and it happens in two stages. The positively charged bit on your electrophile steals the electrons from the double bond, and the H-Br bond breaks. Bromine goes off by himself and finds a carbocation to be attracted to.

#chemistry #mechanisms #Nucleophilic Substitution #elimination #haloalkanes #Electrophilic Addition #alkenes

List Of Equations you need to know for unit 2

Follow the link to this beautiful essential website that is my second home and click on "list of essential equations for unit 2". There's loads of other stuff up on there, so have a look around. It's an awesome website :)

#chemistry #a level #mechanisms #glossary #revision checklist #equations #aqa

THANK GOD FOR YOUR BLOG OMG THANKYOUUUUUUUU, seriously though, it helps me a lot!!XX

Awwwww :') Thank you so much! I'm just amazed people actually look at it to be honest! I'm glad it helps someone! Good luck in the exam next week if you're doing it :) xx

Good old carbocations

Another issue I have is when it asks you which products alkenes produce in electrophilic addition. When the double bond is not in the middle of the chain, more than one haloalkane can be produced.

Why is this? :o

It's to do with the CARBOCATION (positively charged carbon atom)

You have to know that alkyl groups have a "tendency to release electrons" which has a special name

THE POSITIVE INDUCTIVE EFFECT. This electron releasing behaviour stabilises the carbocation, and evens them out so they're balanced...how nice of them... :')

The main product comes from the more stable carbocation!!

So a tertiary carbocation is the most stable because it has the most alkyl groups. (The way I remember this is, that when you're tertiary, you've left school, you're more stable in the way you've stopped growing)

#Electrophilic Addition #carbocations #tertiary #positive inductive effect #alkenes #topic 15 #aqa #chemistry #a level

A haloalkane's favourite mechanism

In which chemistry is compared to the whole school system...

#Haloalkanes #Elimination vs Nucleophilic Substituion #primary #secondary #tertiary #conditions for reaction #topic 14 #aqa #a level #chemistry

List of Equations you need to know for unit 1

Especially for the lovely anon who asked for this, here is a list I put together of all the equations you need to know, or at least be able to manipulate in the AQA Chem Unit 1 exam.

#chemistry #equations #unit 1

How can you tell the difference between a primary, secondary and tertiary alcohol and by any chance would you have a list of equations that we will need to know for the chem1+2? xxxxx

Have you checked out this page on my blog? It's all about telling the difference between a primary secondary and tertiary alcohol. If you already have and you don't understand it, message me and I'll see if I can try and explain it in another way :) I don't have a list of equations (yet) but that sounds like a really good idea! It would help me too as I'm also doing the Chem1 exam. I'll add it to my to do list, make one and get it up on here as soon as I can :) xxxxx

How do you learn the mechanisms : by doing questions or actually memorising where the curly arrows go ??

A mixture of both I think. I find it important to memorize whereabouts the curly arrows go, but say in nucleophilic substitution you had the halogen on a different carbon bond, then the position of the curly arrows is slightly different anyway and that might just throw me off in the exam. But I think it's fine to memorize which types of atom the curly arrows join to and the lone pairs, if that makes sense, so you know what products they form. I'm attempting questions at the same time to try and build my confidence up too, because I don't want to rote learn it. That was a really good question, thank you so much :)

The art of free radical substitution

There's this thing they do to make haloalkanes and it's pretty magical if you think about in a magical imaginative way, because you're bored of staring at a textbook full of numbers and equations.

Making a haloalkane takes place in a few stages and it goes by the name FREE RADICAL SUBSTITUTION.

And of course with any process there is a MECHANISM. That's what they call it in the exam "draw the mechanism for this reaction" "outline the mechanism for this reaction" "state the mechanism for this reaction"

MECHANISM. I mean it's not really a mechanism, is it? They could have come up with a better name to be fair. Something more creative. But anyway MECHANISM is the word they decide to use.

Here's an example of the chain reactions for the free radical substitution reaction:

methane + chlorine ---> chloromethane + hydrochloric acid

The haloalkane is chloromethane.

So how do we make it? You need to be familiar with all the stages:

The first stage is called INITIATION, which I find quite scary when you read it in a deep robotic voice. :o

But it's not really a very scary stage.

Basically UV light is shone on the chlorine, and the chlorine absorbs it and it breaks the bond between the Cl-Cl chlorine molecule to form FREE RADICALS.

A FREE RADICAL is a complicated way of saying an atom with an unpaired electron (highly reactive) They are radical :o because they've lost one of their electrons and they are free because they can go out and REACT with anyone they choose to. Now that is a name in chemistry which I do appreciate.You represent a FREE RADICAL in an equation by drawing a little dot next to show the unpaired electron. There are lots of dots coming up!

If you illustrate that stage as in your "MECHANISM" it looks like this:

(Yes we are going up a notch with the whole black yellow and purple thing ;D I thought I'd try it out)

The next stage happens in two parts, and it's called

PROPAGATION

how proper indeed

The first bit is where the free radical steals a hydrogen atom from methane to form hydrogen chloride, and oh look a GREEN METHYL FREE RADICAL

In the next stage this green methyl free radical is reacted with chlorine:

And this produces your lovely desired haloalkane your chloromethane! (It's desirable so it has flashy sun ray things coming out of it, but please don't draw or write that in your exam, the examiner will think you're crazy)

The last stage is TERMINATION :o

which in my opinion is probably the scariest stage. I mean say that in a scary voice. And the nature of this stage is to get rid of all the free radicals, and I like them so it's kinda sad. But they are very reactive, and they need to be calmed down to stable compounds, so I guess it's necessary.

The termination step looks like this: (fr stands for free radical)

I remember this stage as lumping all the leftover free radicals together and making them react, either with one of themselves or one of each other.

And there you have your mechanism of FREE RADICAL SUBSTITUTION. There's not much point revising these stages off by heart with the equations and everything because in the exam they're likely to give you another free radical substitution with say fluorine, and other new compounds. What is more important is knowing the nature of what goes on in each stage and being able to construct the equations for yourself. So it's best to practice writing out the whole free radical mechanism with the step by step stages initiation, propagation x2 and termination for making haloalkanes you haven't met before. "I just haven't met you yet" ;)

A helpful mneumonic if you're not very good at remembering the order of the stages is

IPT

I play tennis.

Initiation, propagation, termination.

It's kind of crap, but until I think of something more funny or better, I have to resort to I play tennis.

If anyone read or got to the end of this post is good at making mnemonics, and one just appears for IPT in your head however rude, please please message me.

#unit 14 #haloalkanes #free radical substitution #initiation #propagation #termination

Classification of Alcohols

Alcohols are almost ranked into PRIMARY, SECONDARY AND TERTIARY, according to how many other groups are bonded to the carbon that has the -OH group. You have to know how to identify them and I really struggle with that, so I came up with a way of remembering them. It's quite deep, and probably a bit shitty, but it helps me remember them.

This is an example of a primary alcohol (do excuse the shaky paint drawings):

You can see that his -OH group is at the END of the chain. When you're in primary school, say moving up to big school, you come towards the end of fun and games, and childhood. It's quite an emotional way of remembering it, and a bit sad... like primary, end of childhood, but I guess that's why it works.

Here's an example of a secondary alcohol:

This time the -OH group is in the BODY of the chain. Umm, this theory is when you move up to secondary school, you start changing. And somehow popularity, or at least a sense of popularity, becomes all about being pretty and having a nice body- some of the guys start to become obsessed with working out and going to the gym, and some girls seem to dwell on their body image and weight. (This is a very stereotypical assumption by the way, of course not everyone becomes obsessed with their bodies, and that's probably a really really good thing :3)

Here's an example of a tertiary alcohol:

See how the -OH group is positioned at a BRANCH in the chain. When you leave school, you become tertiary. You leave your friends, and school behind, and branch out, "finding yourself" whether it be in a job, an apprenticeship, at sixth form or college, the idea is you're branching out to new situations, meeting new people and finding new friends.

#chemistry #alcohols #topic 16 #aqa #a level #primary #secondary #tertiary #OH functional group

Oh the collision theory...

One day there were two particles casually moving around. For them to collide, they must have enough energy to break bonds, and also be in the correct orientation for the parts reacting together. (My biology teacher uses the example of kissing, because in order for two people to kiss, you obviously have to be in the correct orientation, at least to avoid awkwardness :3) Unfortunatley, most collisions do not lead to a reaction, because they don't have enough energy or are in the wrong orientation :o :'(

There are lots of FACTORS that can be changed though that affect the chemical rate of a reaction:

You will probably be familiar with TEMPERATURE

(They're feeling hot hot hot)

If the temperature is increased, the speed of the molecules increases because they have more kinetic energy. This in turn will increase both their energy and the number of collisions.

Another factor is CONCENTRATION OF A SOLUTION

This is the one we did in our ISA which is basically a practical exam. If you increase the concentration, there are more PARTICLES PRESENT IN A GIVEN VOLUME, and collisions are more likely so the rate of reaction increases yayy :D

However, this will not last forever because the reactants are used up and the rate of reaction falls.

The next one is PRESSURE of a GAS REACTION

Just think of the song sung by Jedward- not the original version because the Jedward one is more annoying and gets in your head ;)

"Under pressure, pushing down on you, pushing down on me"

So basically you are squishing the particles together, scientifically "there are more particles present in a given volume" so collisions are more likely and the rate of reaction increases. Everybody's happy :D

Just look at them all snuggled up there, getting close :')

You could also increase the SURFACE AREA OF SOLID REACTANTS.

So say you got a big fat lump of something, grinding it up into a powder means there are more sites for reaction and more of it's particles are available to collide. This increases the rate of reaction :)

Using a catalyst:

DEFINITION: a substance that speeds up the rate of reaction but is not used up

(In my head it looks like this- a kind of cat shaped substance that comes to save the day :3 but if that just distracts you and makes you think about cats that's probably not great because catalysts have nothing to do with cats whatsoever)

Then you have to know about ACTIVATION ENERGY. This is the special energy the molecules need in order to start a reaction. It's like the passion, the firey stuff before going into a reaction ;)

BUT PLEASE DON'T WRITE THAT IN YOUR EXAM THE EXAMINER MAY GET THE WRONG IMPRESSION :o

In the exam please write "The activation energy is the minimum energy required/needed to start a reaction"

The symbol for this is:

If you have time you should watch this

#chemistry #kinetics #collision theory #temperature #pressure #concentration #surface area #catalyst #activation energy #topic 8 #a level #AQA

ELECTROPHILIC ADDITION OF ALKENES

One day an alkene was just trollollolling along, minding his own business, as alkenes do. What he didn't realise that the double bond C=C he posessed in his stomach, was actually a really HIGH AREA OF ELECTRON DENSITY :o

An area that ELECTROPHILES are attracted to. An electrophile is an electron-deficent species that takes part in an organic reaction by attacking areas of high electron density in another reactant. :o An example of an electrophile is HBr, hydrogen bromide.

This electrophile was all alone. He only had a partially positively charged area. All he wanted was some company from some fellow electrons. He couldn't help but be attracted to the double bond in the alkene.

Fortunately, the alkene could sympathize with the electrophile. The electrophile accepted a pair of electrons kindly donated by the double bond in the alkene.

The alkene had been hoping for change, some transformation. He was bored of the alkene life. He wanted to be free. He wanted to grow up to be a haloalkane ever since he was little boy.

In order for this to happen, a positive ion a CARBOCATION forms. A negatively charged ion (in this case Bromide) and forms a bond with the carbocation.

And everyone lives happily ever after.

#chemistry #electrophilic addition #alkenes #carbocation #topic 15 #a level #as

Using Thermochemical Cycles

There are probably lots of different ways of working this out, the one in my textbook actually looks really complicated, but this is the way our teacher told us to use it and remember it.

An example question might say "Use the table to calculate the standard enthalpy of formation of *insert chemical*"

Then they'll give you a little table of some data, say the enthalpy of combustion KJmol-1 for some chemicals.

The thing I struggle with is which method to use, the enthalpy of formation, or the enthalpy of combustion? But no matter what the question asks you, you do whatever data they give you. If they give you combustion data, use the combustion method. If they give you formation data, use the formation method.

So...

for THE ENTHALPY CHANGE OF COMBUSTION

-your arrows go DOWN (because things burn down)

-and you use the "1,2,3" equation

(Enthalpy change 1 = enthalpy change 2 - enthalpy change 3)

E.g

So you'd just plug in your values from the table that they give you into that equation.

THE ENTHALPY CHANGE OF FORMATION

-The arrows go up FORM UP (If you've ever played that flying game on wii sports resort, there's a voice and it goes "everybody form up" and then they all put their arms up and parachute. That's how I remember it anyway...)

-And you use the equation 1,3,2

E.g.

That probably didn't make much sense whatsoever, but yeah. That's how I would do it.

#chemistry #enthalpy of formation #enthalpy of combustion #thermochemical cycles #hess's law

Hess's Law

Hess was a Russian chemist who came up with a law. You need to know the definition. There are several different ones, but the mark scheme says

"The enthalpy change in a reaction is independent of the route taken" is acceptable and I think it's probably one of the easiest to remember.

I made a revision card it's not stuck up, laminated in my shower, I promise :3 which looks like this:

(I did debate including an actual photo of Hess, but then I thought if I was a chemist born in 1802, would I really want a future person looking at a photograph of me in the shower, naked with their theory they need to learn for their exam. And I found that all a bit weird so I decided on a representative paint drawing)

Moving on.. so how do you use Hess's Law?

You draw out thermochemical cycles for the equation to basically draw the different "routes" a reaction can take.

#chemistry #hess's law #definition

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An attempt at passing AS chemistry