Chemistry

Orlaladuck

Since the Guidance counselor thread turned into a chemistry debate I decided to just make another thread for it.
I find it really difficult to understand and that's where I fall down in it. Also I'm not exactly what you'd call thick either or lazy - I get between A's and C's in most other subjects- my teacher's fairly okay and the revision books are quite helpful - so where's the problem here? :cool:

felic

Could you be more specific? Like what area of it exactly is confusing you and causing difficulty?
I think with chemistry it really depends on the teacher and the order in which they teach you the material. I ended up having to get grinds when I was doing mine because I really hadnt a clue in class. The problem was that our teacher started off the course with stochiometry.. that was fine, but then he began to really focus on Organic. And in the final months of 6th year, he went back over the periodic table, atomic structure, gases, etc.

I agree that Organic can be tricky but if you have done the ground work with the earlier more basic topics, you will understand why things happen in organic the way they do.

If you're struggling, seriously consider a grind for say an hour every saturday morning or something. It really helped me. Also, there are certain sections you can leave out in terms of the paper so focus on going over exam papers too

jumpguy

I think before organic chemistry it's definetly handy (maybe even nessicary) to have electronegativeity done.

Anyway, as you haven't stated what parts of chemistry cause trouble, the advice for nearly everything is try to understand it. It's extremely difficult to rote learn chemistry, which is why it's kinda unique in comparison to other science subjects, where there's alot you can just learn off without really understanding.

Orlaladuck

Can't afford grinds. I'm already paying 65 a week between maths grinds and driving lessons so my parents won't be so happy if i ask for another 30-40 an hour grind.
But I wasn't talking about me here anyhow - I'm well aware i'm screwed at this point and i'll probably get by with a low C. But it was said in the other thread why people should and shouldn't take it and I was just using myself as an example as one of those people who takes it and Should have no problems with it based on other people's usual reasons as to why they don't do well in other science subjects such as bad teaching, class numbers etc.

seanaor

Did you choose chemistry because you like it or because you need it for college? There are 12 in my class, and its those that like it that top the class. I dont think its coincidence...

Orlaladuck

At the time I wanted to be a vet but halfway through 5th year I changed my mind and it was too late to drop it and if I had I would've lost LCVP so I really couldn't win =[. I've told many a cousin since to not do it unless they're completely sure they want to and are generally good at maths/science.

ayumi

i choose chem as i had to have it for college and problem is i study the chap and when i come to answer the exam papers i forget everything.
heat of formation & combustion & octane number is the hardest for me and i studied it but in the debs mock a q came and i couldnt it

_Bella_

I think when it comes to chemistry the main bulk of the class does it because they need it for their course.

Konata

I loved Chemistry but there are parts of it that are quite tricky. For me and most of class, it really all came together in the last month or 2 before the LC. Once you have the whole course done and start to go back over things from the beginning and link them in with later stuff, it all starts to make alot more sense. You can understand how it all 'works' I guess. So don't give up hope yet, just keep ooking over what you've done so far, concentrating on the basics of each sectiona and hopefully it'll all just click together soon. There's still a few months to go yet so plenty of time to get your head around it.

felic

The Chemistry paper now is really geared to give you the marks... not really test you in terms of having a scientific mind.
With Chemistry, learning off definitions is part of the process, but as well as learning them off, you have to actually know what they mean. That may sound ludicrous but it happens in other subjects. Not with Chemistry.

I can see as well how converting the units can be difficult and confusing. Thats just practice and being familiar with what they ask. Units are SO SO SO important. Like when you're answering a definition question... you nearly have to list several steps.
1. The printed definition in the book
2. A general formula..
3. An example
Always put the units in for any question that asks for a definition like this

Example..
Define Heat of Formation of a compound
Answer
The Heat of formation of a compound is the heat liberated when 1 mole of the compound is formed from its elements in their standard states.

C (gas) + O2 (gas) -> CO2 (gas)
H2 (gas) + O2 (gas) -> H2O (liquid)

The heat changed is measured in units of kJ/mol and can be either an endothermic (-) or exothermic (+) reaction.

----
Theres nothing complicated in that answer but it shows you know what you're talking about and with these exams, its all about 'showing off how much you know'.

Im not sure if its necessary any longer, but those students going for an A1 really need to hammer home that final baseball hit, so for someone who is really into this stuff, get online and go a little outside the syllabus or look at university text books for little pointers.

Like say you're answering a question on elctron structure and position in orbitals of sublevels outside the radius.
Theres only sublevels s p d f on the LC course but theres actually 3 more after these... s p d f g h i
If you list all these you will really impress the marker. And then you could make reference to Paulis exclusion theory and the Hunds repulsion theory when taking about where the electrons are in orbit but throw in an extra fact of electron size to show you have really researched this stuff.
Theres a whole bunch of complex formulae to give these numbers and just learning one or two and throwing em down will really make you stand out.

Konata

felic wrote: »

Im not sure if its necessary any longer, but those students going for an A1 really need to hammer home that final baseball hit, so for someone who is really into this stuff, get online and go a little outside the syllabus or look at university text books for little pointers.

Like say you're answering a question on elctron structure and position in orbitals of sublevels outside the radius.
Theres only sublevels s p d f on the LC course but theres actually 3 more after these... s p d f g h i
If you list all these you will really impress the marker. And then you could make reference to Pauis exclusion theory and Heisenbergs repulsion theory when taking about where the electrons are in orbit but throw in an extra fact of electron size to show you have really researched this stuff.
Theres a whole bunch of complex formulae to give these numbers and just learning one or two and throwing em down will really make you stand out.

Sure it'll impress the examiner but it won't gain you any extra marks. The examiner has to stick by the marking scheme (which is based on the syllabus) and there aren't any 'bonus points' for extra info. If you list the sublevels as s p d f g h i, you'll get the same amount of marks as someone who lists only the ones on the syllabus.

It's not really worth your time learning anything outside the syllabus - plenty of time for that in college. I got an A1 in Chemistry just by sticking to the syllabus and keeping at it.

dambarude

felic wrote: »

Theres a whole bunch of complex formulae to give these numbers and just learning one or two and throwing em down will really make you stand out.

This couldn't be a good idea. Chemistry has one of the most precise and pinpointed marking schemes in the whole LC. Certain words and sentences are awarded marks. Superfluous information won't get you anything.

I loved chemistry because it was so to the point- no waffle, just write down the (correct) answer and you should get your marks. It's either right or its wrong for the most part. (Not like the silly English exam:rolleyes:)

felic

Ah ok. Well in the past, questions outside the syllabus were asked and u were expected to make educated guesses at what the result would be. Guess that was deemed unfair and taken away.
With the current exam its a walk in the park to get an A1.

dambarude

felic wrote: »

Ah ok. Well in the past, questions outside the syllabus were asked and u were expected to make educated guesses at what the result would be. Guess that was deemed unfair and taken away.
With the current exam its a walk in the park to get an A1.

The syllabus changed in the early 2000s if I remember correctly. I don't think they'd get away with putting anything on any exam that isn't on they syllabus anymore. It's not particularly fair.

Admittedly, Chemistry is far from the hardest subject to get an A1 in. The figures speak for themselves. But you have to look at the population of LCers that actually take Chemistry- it is very narrow, and probably consists mostly of students who do fairly well overall.

dambarude

I just had a look at the 1996 HL Chemistry paper there. It didn't seem very different to the newer paper at all. There are areas on the 1996 paper that aren't on the newer syllabus, but the standard of the comparable questions seems quite similar. The older paper required you to answer 5 out of 10 questions, the newer paper requires 8 out of 11.

A Neurotic

Chemistry is definitely the paper with the most choice - it was out of my 7 subjects, anyway. With this in mind, I pretty much ignored most of Atomic Theory as it wrecked my head and got an A1. Play to your strengths.

H2student

Out of all my subjects, I think Chemistry is the most difficult subject to understand. However, I'm aiming for an A1 in the exam because I think the paper is really nice .

I like it how there's an almost guarantee on what topics comes up every year.

Q1-3 Experiments (which are divided into Titrations + (making something :P), Organis and the rest of the exp)

Q 4. Short questions (I hate it)

Q 5. First few chapters of book (Periodic table/intermolecular forces etc.)

Q 6. Fuels + thermochemistry ( Love it! Short and easy chapter with predictable questions. They asked "define octane number" so many times.)

Q7/8 General Organic (bleh....)

The rest is on the rest of the course I guess. From my analysis of the papers, Chemical Equilibrium comes up as a full question or a half-question. - unless the experiment comes up. (I find it very manageable, since it's a very logical and short chapter)

From what I can see, that's 7 almost definite questions out of 8 .

The syllabus change was in 2002 I think, they did ask a question that was specified specifically on the syllabus that it doesn't need to be learn. They end up giving it very little/if any marks for it. I think it was to explain why bromine water can test for saturation. (don't quote me on this.)

rainbowtrout

felic wrote: »

Ah ok. Well in the past, questions outside the syllabus were asked and u were expected to make educated guesses at what the result would be. Guess that was deemed unfair and taken away.
With the current exam its a walk in the park to get an A1.

It's not a walk in the park by any means. It can't be a fair exam if questions outside the syllabus are asked. How are students supposed to be assessed equally and fairly on material that some may have been taught and some not?

There are no extra marks for extra information, your answer is in the marking scheme or it's not. It's that simple.

To the OP - as a chemistry teacher, I don't think the concepts are overly difficult in chemistry, and while a good grasp of science and maths helps significantly, really it's being able to understand logical patterns that makes everything click into place.

I see students who are clever, who can learn stuff off, can apply and manipulate formulas, but when it comes to application of knowledge they fall down.

Some students do genuinely find it difficult to make the connection between concepts

Eg: Reactivity of the Alkali Metals: In group 1 of the Periodic Table elements become more reactive with water as you go down the group.


Ionisation Energies: The ionisation energy of Potassium is less than that of Sodium

Electrons that are further away from the nucleus are easier to remove, due to screening etc.

Many students fail to connect the three statements (or similar) or that potassium reacting with water is a reaction is which an electron is being removed etc etc.

Many students will try and learn off trends in the PT, instead of trying to understand why the trends happen, instead of looking at the numbers to see what is happening to them, or thinking about the structure of each of the atoms.

There are plenty of examples of this type of thinking throughout the course, but I think that is a large part of the problem

Rossie17

The course doesnt need us to know these things which is a bit annoying, I think I would be A1 at chemistry if it wasnt about such precise english. Like, using a wash "bottle", or a "funnel" these words alone are often worth 3 marks each, which is crazy. You could write "I like my funnel" = 3 marks; or "Im going on the wash bottle after this"...

rainbowtrout

Rossie17 wrote: »

The course doesnt need us to know these things which is a bit annoying, I think I would be A1 at chemistry if it wasnt about such precise english. Like, using a wash "bottle", or a "funnel" these words alone are often worth 3 marks each, which is crazy. You could write "I like my funnel" = 3 marks; or "Im going on the wash bottle after this"...

I'd disagree to a certain extent. If you are studying chemistry or go on to a degree in science/work in a lab, the very least you should know is the names of the pieces of equipment you are going to use.

Lawliet

rainbowtrout wrote: »

I'd disagree to a certain extent. If you are studying chemistry or go on to a degree in science/work in a lab, the very least you should know is the names of the pieces of equipment you are going to use.

T'would be very amusing if they didn't though
"Hey has anyone seen those liquid holder yokes? You know the ones with the liquid sucker-up thingies at the top?"
"Oh yeah, they're over in that press next to the roundy glass bottles with the caps, and above the standy clampy things"

felic

hee hee... imagine a student writing that in an exam..

"you fill the long glass tube thing with water and then turn the tap yoke so it falls into the cone flask. then the mixture reacts and steam comes off it and travels through another glass tube with water flowing around the inside of it and then it drops down into this glass cup yoke at the end. You then get this skinny class tube thing and with a squishy rubber ball, you stick that on top of the skinny tube and squeeze it so the liquid in the cup comes up into the skinny tube"

LOL!!!! Full marks!

Messi 10

felic wrote: »

The heat changed is measured in units of kJ/mol and can be either an endothermic (-) or exothermic (+) reaction.

You have those the wrong way round. Exothermic is (-) and endothermic is (+)

felic

ol. Oh my God ur right... and Ive a degree in the stuff! typo's I swear it! Well u can forget my earlier post anyway cos apparently the marking schemes are now very much A or B type answers. You have the right word or you dont. 0 marks for everything else which seems whack to me to be honest.

ed42167

my god started the course with stoichiometry??
that would so have turned me off! we started from the basics (periodic table etc.)
Our class dont have an actual chemistry book. instead we work from notes our teacher writes out and photocopies. 2 lever-arch files later and im starting to struggle. Background information (and lots of it) helps me understand chemistry

Lawliet

Our class started with the ordinary level titration's, which was awesome! I think everyone in the class like "Now this is what we've been waiting for since first year!"
Then we went back to the history and periodic table stuff.

Rossie17

rainbowtrout wrote: »

I'd disagree to a certain extent. If you are studying chemistry or go on to a degree in science/work in a lab, the very least you should know is the names of the pieces of equipment you are going to use.

Oh I know you should know the equipment, just that the word alone gets you the marks. You should need sentences at least. I used a bad example for the precise english, how about the dont say clear its colourless, dont say purple its pink in the marking scheme etc. I mentioned the wash bottle because you need to bring everything up to the meniscud with a wash bottle, but If you said "add drops of water slowly to the volumetric flask until the bottom of the meniscus of the solution reaches the mark" = 3. Some guy says "washbottle" + "bottom of meniscus" = 6.

H2student

washbottle? O_O I thought it was dropper!

felic

Our chemistry teacher was just awful. I mean, he was a nice guy and knew his stuff but just couldnt teach it. about 25 started in 5th year and by the christmas it was down to about 15 and only about 9 of us took the higher paper in the end, best result being a B2. But that was the old course and the paper we had had so much organic on it, it wasn't funny... me being deluded enough to think it was ok to leave organic out. DONT LEAVE ORGANIC OUT!

The history stuff is boring and tiresome. Ask your teacher to do a print out of pictures of all these guys you need to remember and just words next to them for what they did. Then just look and read over that page everyday between now and June... that way you're not learning stuff off like a nursery rhyme but more learning by recognition.

Alice10

does anyone know the equation for the combustion of methane???

seanaor

Ch4 + 2o2 -> co2 + 2h20

My bad.

Alice10

thanks. and do you have to balance that before you start you know them things with Delta H ?! sorry i know that doesnt really make sense

H2student

eh? Are you talking about thermochemistry.

Not sure if you're asking this but if the question says:

The heat of combustion for Methane is (say) 5 KJ mol^-1, then that is the value for the balanced equation. Also, I think you need to learn how to balance combustion reactions yourself, since they can ask it for almost any hydrocarbons and it's relatively straightforward to do.

Alice10

the Q is : write a balanced equation for the combustion of methane. if the heat of combustion of methane is -890kJ mol-1 , etc
i jus need to know the balanced equation for the combustion of methane, i know i to work the rest of it out

jumpguy

Methane is CH4.

A hydrocarbon burns to give water and CO2. You need oxygen to burn things.

CH4 + 2O2 = 2H20 + CO2

Alice10

thanks

do you know what thing has an octane number of 100 ?

Making It Bad

If you're struggling make sure you have the basics down and understand it all: electronegativity, chemical bonding, periodic table, mole concept and so on (in other words the first few chapters of your book). For example, you have no hope of learning how to name the alcohols if can't name the corresponding alkanes, or you have no hope in understanding why they mix with water if you don't understand electronegativity. The subject really builds on it self, which is why if you didn't work in 5th year of chemistry you're struggle with the 6th year stuff even though it isn't actually harder.

seanaor

Alice10 wrote: »

thanks

do you know what thing has an octane number of 100 ?

2,2,4 trimethylpentane!

Making It Bad

Alice10 wrote: »

thanks

do you know what thing has an octane number of 100 ?

trimethyl pentane I believe

Edit: seanaor beat me to it

Alice10

Thanks
are you supposed to learn those off or is there a way to make them out?! :S

Do you know what a LPG is?
it says name 2 components of LPG

Making It Bad

Alice10 wrote: »

Thanks
are you supposed to learn those off or is there a way to make them out?! :S

Do you know what a LPG is?
it says name 2 components of LPG

Use google, "Liquefied petroleum gas, propane and butane". I don't think those kinda questions would come up on the L.C

felic

LPG - liquid petrolium gas - are u sure the question is not asking what are the 2 main components of LPG? Butane and isobutene and then mercaptan is added to give it a strong odour for fast detection of leakages. Is this the option stuff of the course?

CNG - compressed natural gas - methane.

seanaor

Alice10 wrote: »

are you supposed to learn those off or is there a way to make them out?! :S

You just need to know what has an octane number of 0 (heptane) and 100 (trimethylpentane). Theres no method on the syllabus to work them out...

Itd also be wise to learn the four methods of increasing the octane number of a fuel!

Fad

Alice10 wrote: »

does anyone know the equation for the combustion of methane???

An alkane burns in air to form carbon dioxide and water.

CH4 + 2O2 -> CO2 + 2H20

Seriously though, if you cant figure that out at this stage, I'd worry.

Never looked at the 3rd page of the thread *facepalm*

rainbowtrout

Alice10 wrote: »

Thanks
are you supposed to learn those off or is there a way to make them out?! :S

Do you know what a LPG is?
it says name 2 components of LPG

No offence Alice, but it sounds like you're getting other people (who have been very helpful here) to do your homework. You're far more likely to remember it if you get off the computer and open your chemistry book and look it up. you're going to find it pretty hard in June if you are struggling with the basics at this point of the year.

@everyone else, i think that series of questions was a leaving cert organic question from a couple of years ago, possibly the 02 paper, the first year it was examined- they did ask what does LPG stand for!:eek:

EDIT: yep, it was

http://www.examinations.ie/archive/exampapers/2002/LC022ALPO00EV.pdf

seanaor

I was thinkin that series of q's was familiar...that was part of my xmas test. Ha!

Alice10

rainbowtrout wrote: »

No offence Alice, but it sounds like you're getting other people (who have been very helpful here) to do your homework. You're far more likely to remember it if you get off the computer and open your chemistry book and look it up. you're going to find it pretty hard in June if you are struggling with the basics at this point of the year.

@everyone else, i think that series of questions was a leaving cert organic question from a couple of years ago, possibly the 02 paper, the first year it was examined- they did ask what does LPG stand for!:eek:

EDIT: yep, it was

http://www.examinations.ie/archive/exampapers/2002/LC022ALPO00EV.pdf

Excuse me for your information I have my Chemistry book open in front of me an have been studying all nigth. The only reason I asked the questions on this is because I cannot find the answers in the book! and no, it is not not homework nor would i get people here to do my homework for me. I am revising a topic we covered last year - nothing whatsoever to do with what we are doing in school at the moment!
And no where in my chemistry book does it Explain what LPG is hence me asking the question

Making It Bad

rainbowtrout wrote: »

@everyone else, i think that series of questions was a leaving cert organic question from a couple of years ago, possibly the 02 paper, the first year it was examined- they did ask what does LPG stand for!:eek:

EDIT: yep, it was

http://www.examinations.ie/archive/exampapers/2002/LC022ALPO00EV.pdf

Eugh, that sucks. I've never seen that in my textbook. Hate all those stupid little weird memory questions.

felic

So.. proof of my points earlier that they DID ask stuff that wasnt on the syllabus! I saw a question on one of the recent papers as well asking for the octane number of some compound. Thats not on the LC course either!

jumpguy

Alice10 wrote: »

the Q is : write a balanced equation for the combustion of methane. if the heat of combustion of methane is -890kJ mol-1 , etc
i jus need to know the balanced equation for the combustion of methane, i know i to work the rest of it out

Alice10 wrote: »

thanks

do you know what thing has an octane number of 100 ?

Alice10 wrote: »

Excuse me for your information I have my Chemistry book open in front of me an have been studying all nigth. The only reason I asked the questions on this is because I cannot find the answers in the book! and no, it is not not homework nor would i get people here to do my homework for me. I am revising a topic we covered last year - nothing whatsoever to do with what we are doing in school at the moment!
And no where in my chemistry book does it Explain what LPG is hence me asking the question

What chemistry book do you have? It must be fairly crap if it doesn't explain burning hydrocarbons in oxygen, or what is used in comparison octane tests (octane number 100)?

BTW Making It Bad, you need to have the 2, 2, 4 in trimethyl pentane (2, 2, 4 trimethyl pentane). Correct me if I'm wrong someone though!

dambarude

felic wrote: »

I saw a question on one of the recent papers as well asking for the octane number of some compound. Thats not on the LC course either!

Octane numbers are on the LC course though