AS OCR chemistry B (SALTERS) F331 on the 15th may 2012

Reply 580

SimpleGirl

3

Original post by ells-13

If they would have put 2-methylbutane I would have got the mark but they didn't which confused me :s-smilie:

Original post by Salmonidae

Yets it's because methyl-butane only has one possible structure :tongue:

He's right. To be methylbutane, the methyl group has to go on either of the middle 2 carbons, but either way it'll still be 2-methylbutane so the '2' is unnecessary when naming.
I knew this as well, but I just wasn't thinking properly and thought 'oh, it doesn't have a number so I'll just stick it on the first carbon' :facepalm:

Reply 581

MD2807

Original post by matty b

What were the 3 marks for in the bond angle question? Would putting the wrong angle (ie 104.5) get any marks, provided you explained it right (given the confusion around the question)?

hopefully like an error carried forward type thing

Reply 582

Adamcfc

******************************************************

Right, cant believe were still arguing about this bond angle question :L

I sat down with my teacher today and a copy of yesterdays paper, here is the exact question, as it was worded in the exam..

Sulfur Hexafluoride is used in some types of eye surgery.

Use the electron pair repulsion principle to predict and explain the shape of the Sulfur Hexafluoride SF₆ molecule and suggest the F-S-F bond angle.

Now you may interpret the question in your own way, but in my eyes, and the eyes of my chemistry teacher, its clearly talking about the F-S-F bond in the hexafluoride molecule, which would be 90 degrees.

He also thought the marking points would be as follows, so for people putting 107, or 180, there are still a possible 3/4 marks so dont panic.

•

90 degrees

•

6 electron groups (around central S atom)

•

electrons are negative

•

therefore repel and arrange themselves as far apart as possible

Dont mean to offend anyone, just trying to clear it up.

******************************************************

Reply 583

06ollie

Original post by ItsBezaaa

They must allow that though! Quite a lot of people wrote that :colondollar:

[/Q

That's not usually the way they mark these things :P And no, it's definitely octahedral

Reply 584

matty b

Original post by Adamcfc

******************************************************

Sulfur Hexafluoride is used in some types of eye surgery.

Use the electron pair repulsion principle to predict and explain the shape of the Sulfur Hexafluoride SF₆ molecule and suggest the F-S-F bond angle.

•

90 degrees

•

6 electron groups (around central S atom)

•

electrons are negative

•

therefore repel and arrange themselves as far apart as possible

******************************************************

Thanks for clearing it up, and looking back now i am ashamed to have got this wrong.

Reply 585

master_blaster66

17

Original post by Adamcfc

******************************************************

Right, cant believe were still arguing about this bond angle question :L

I sat down with my teacher today and a copy of yesterdays paper, here is the exact question, as it was worded in the exam..

Sulfur Hexafluoride is used in some types of eye surgery.

Use the electron pair repulsion principle to predict and explain the shape of the Sulfur Hexafluoride SF₆ molecule and suggest the F-S-F bond angle.

Now you may interpret the question in your own way, but in my eyes, and the eyes of my chemistry teacher, its clearly talking about the F-S-F bond in the hexafluoride molecule, which would be 90 degrees.

He also thought the marking points would be as follows, so for people putting 107, or 180, there are still a possible 3/4 marks so dont panic.

•

90 degrees

•

6 electron groups (around central S atom)

•

electrons are negative

•

therefore repel and arrange themselves as far apart as possible

Dont mean to offend anyone, just trying to clear it up.

******************************************************

electrons are negative?...i think most markschemes say you get a mrk for stating that the electrons repel

Reply 586

s.aley

Original post by ItsBezaaa

They must allow that though! Quite a lot of people wrote that :colondollar:

i dont understand why you think they would allow that

Reply 587

Adamcfc

Original post by master_blaster66

electrons are negative?...i think most markschemes say you get a mrk for stating that the electrons repel

Top of page 8

http://www.ocr.org.uk/download/ms_11/ocr_65223_ms_11_gce_uf331_jun.pdf

but yeah its usually something along those lines

Reply 588

The Moleman 99

I accidently wrote around the central C atom. Doh! Lets hope my C looked like an S :colondollar:

Reply 589

TheStudent.

13

Original post by Adamcfc

******************************************************

•

90 degrees

•

6 electron groups (around central S atom)

•

electrons are negative

•

therefore repel and arrange themselves as far apart as possible

Dont mean to offend anyone, just trying to clear it up.

******************************************************

I disagree. The four marks would be awarded as follows:
- SF6 has an OCTRAHEDRAL shape
- Bond angle of 90 degrees
- Electrons repel
- Arrange themselves as far apart as possible to minimise repulsion

(edited 11 years ago)

Reply 590

TheStudent.

13

Original post by SimpleGirl

I was resitting this paper too. I did it first time round last June. (Which, obviously, looking back now I was mortified about how I didn't get a higher grade considering the June '11 paper wasn't bad at all).

And I agree with you, those were the things that mainly threw me off as well.
But, I've also realised that I made some other silly mistakes. Like, was I the only idiot that put the methyl group on the first carbon when they asked us to draw the full structural formula of methylbutane?
That was one of the first things we learnt in chemistry as well, what a stupid mistake. I feel so ashamed. :facepalm:

Yehhhhh most of the questions in june 2011 were repeats of questions found in past papers but just rephrased differently. I keep kicking myself for not doing past papers last year.

Awwwww! Don't worry about it :smile:

It was only 1 mark :wink:

and plus everyone makes mistakes like those under exam conditions, and this thread is testimony to that. I've learned to read the question three times over lol. In fact, my sister lost 2 easy marks because she thought they wanted her to draw the structural isomers of methylbutane, instead of octane, simply because she hadn't read the question properly.

Edit: Oh damn! I just clocked what you were talking about :redface:

. I thought you meant you drew it as CH3-CH2-CH2-CH2-CH3.......... noooooooo I made the same mistake lol. I wasn't thinking! I made the presumption that, as in alcohols, if a group is on the first carbon, you don't have to number it. But as I said, its only 1 mark :wink:

so dont stress! :biggrin:

(edited 11 years ago)

Reply 591

3raindrops

I really liked this paper, everything I revised came up, I made a few silly mistakes like the bond angle, even though I drew it out and everything with the 4 in plane, one wedge, one behind plane. Hopefully I'll get the rest of the marks for making all the generic points.

I also messed up the calculations, but once again hoping I get marks for the method/formulas used.

I hope I get an examiner willing to read and understand my working out, and not be lazy about the whole thing. Would be definitely disappointed if I dont get an A! Now [impatiently] waiting for 16th August.

Reply 592

TheStudent.

13

Original post by twizzzzzzter

Lmfao, you're such a pube,
<implying you could do a thing to anyone
<implying anyone is scared of you

I did?

Well if you intepreted it that way, thats your prerogative, but I was actually implying that GCSEs is not a measure of common sense. Sure you can be intelligent, but that doesn't mean your head isn't full of aerosol when it comes down to general knowledge.

Reply 593

Lucy25021

I also sat down with my chemistry teacher who said there's two ways of interpreting the question. He thinks people will probably get the marks for both. Although just to clear things up, for those who says SF2 doesn't exist - it does, Sulphur Difluoride.

http://en.wikipedia.org/wiki/Sulfur_difluoride

Reply 594

craycray

Original post by The Moleman 99

I accidently wrote around the central C atom. Doh! Lets hope my C looked like an S :colondollar:

OMG I just realised I did that tooooo :frown:

*facepalm*

Reply 595

SimpleGirl

3

Original post by TheStudent.

Yehhhhh most of the questions in june 2011 were repeats of questions found in past papers but just rephrased differently. I keep kicking myself for not doing past papers last year.

Awwwww! Don't worry about it :smile:

It was only 1 mark :wink:

and plus everyone makes mistakes like those under exam conditions, and this thread is testimony to that. I've learned to read the question three times over lol. In fact, my sister lost 2 easy marks because she thought they wanted her to draw the structural isomers of methylbutane, instead of octane, simply because she hadn't read the question properly.

Edit: Oh damn! I just clocked what you were talking about :redface:

. I thought you meant you drew it as CH3-CH2-CH2-CH2-CH3.......... noooooooo I made the same mistake lol. I wasn't thinking! I made the presumption that, as in alcohols, if a group is on the first carbon, you don't have to number it. But as I said, its only 1 mark :wink:

so dont stress! :biggrin:

Yeah, I spent my time after the exam just sulking over the stupid mistakes but yesterday I got some very productive revision done so hopefully the rest of my exams go well.

And unfortunately, I don't think the methylbutane question was the only silly mistake I made so I'm certain it's not just one mark I've lost :frown:

Though, this exam has made me more aware now to make sure I don't let stupid things like not reading the question properly or 'I wasn't thinking' be an excuse to lose more marks next time.

Good luck with the rest of your exams! :smile:

Reply 596

SimpleGirl

3

Original post by TheStudent.

I disagree. The four marks would be awarded as follows:
- SF6 has an OCTRAHEDRAL shape
- Bond angle of 90 degrees
- Electrons repel
- Arrange themselves as far apart as possible to minimise repulsion

I agree. I think these are the 4 points you'd get marks for.

EDIT: Actually, I'm sure there's always a mark for saying the number of groups/sets of electrons around central carbon, so wouldn't that be one mark?
Maybe saying 'electrons repel as far as possible' is one mark, as opposed to 2 separate marks? :dontknow:

(edited 11 years ago)

Reply 597

SimpleGirl

3

Original post by Adamcfc

Sulfur Hexafluoride is used in some types of eye surgery.

Use the electron pair repulsion principle to predict and explain the shape of the Sulfur Hexafluoride SF₆ molecule and suggest the F-S-F bond angle.

•

90 degrees

•

6 electron groups (around central S atom)

•

electrons are negative

•

therefore repel and arrange themselves as far apart as possible