OCR B F335 - Chemistry by Design - 13th June 2012

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Reply 380

Princess Kawaii

Original post by master_blaster66

F would be -2..you ignore the no. of moles

yep that's what I thought...some times I confuse myself :rolleyes:

thanks

Reply 381

master_blaster66

Original post by Beffnaay

Wouldn't F just be -1?

yh F by itself would be -1..but the question says F2 so therefore its -2

Reply 382

Princess Kawaii

Original post by Beffnaay

Wouldn't F just be -1?

it usually is but in the example I gave: 2CuF2

F has a little 2 after it so there is two of them in that compound and so its -2
:smile:

(edited 11 years ago)

Reply 383

Waki

Anyone help with Kc units!
I dot get how you end up with the numbers on moldm! :/

This was posted from The Student Room's iPhone/iPad App

Reply 384

Huffers

i knoww ive had the same problem, just now did the jan 2012 paper and there was one i swear it had one on top and 2 underneath so i cancelled some out to make mol-1dm3 but it was something odd like mol-2dm5??

Reply 385

Princess Kawaii

Original post by Waki

Anyone help with Kc units!
I dot get how you end up with the numbers on moldm! :/

This was posted from The Student Room's iPhone/iPad App

For example Equation: PCl5--->PCl3 + Cl2

Kc = [PCl3][Cl22] / [PCl5]

Use the above and just replace with units. The unit of Kc is always moldm^-3

So Kc: (moldm^-3) (moldm^-3) / (moldm^-3)

Cancel them out (moldm^-3) ~~(moldm^-3)~~ / ~~(moldm^-3)~~

Now your left with one moldm^-3. Those are your units.

Hope that helps :smile:

Also when you get the "odd" numbers for moldm...it means that you hade more units left at the bottom than at the top of the equation, so you have to add them together and then bring them to the top, which switches the signs on the mol and dm. (if that makes sense)

(edited 11 years ago)

Reply 386

Huffers

How about this question from jan 12 Kc=(CH3OH)/(CO)(H2)2

Calculate the value of Kc and give its units, calculated it right but got units
mol-1dm3 when the answer is dm6mol-2??

Reply 387

Princess Kawaii

Original post by Huffers

How about this question from jan 12 Kc=(CH3OH)/(CO)(H2)2

Calculate the value of Kc and give its units, calculated it right but got units
mol-1dm3 when the answer is dm6mol-2??

Okay...just follow the steps

Replace the values with the units so you get:

Kc= moldm-3 / (moldm-3) (moldm-3)2 <--- that is squared so mulitply the brackets out to get :

Kc= moldm-3 / (moldm-3) (moldm-3) (moldm-3)

Cancel out :

Kc= ~~moldm-3~~ / ~~(moldm-3)~~ (moldm-3) (moldm-3)

You're left with (moldm-3) (moldm-3) at the bottom of the equation

Now you add them together to get mol2dm-6

But you have to take it to the top of the equation, so the signs flip to make your units

mol-2dm6

Hope that helps :smile:

Reply 388

katiecornish

Does anyone know the A* grade boundaries?!

Reply 389

master_blaster66

Original post by katiecornish

Does anyone know the A* grade boundaries?!

they vary all the time..but um is always 90% which is 108/120

Reply 390

katiecornish

Original post by master_blaster66

they vary all the time..but um is always 90% which is 108/120

No idea what the average raw mark conversion for 108ums is then? :frown:

cannot find them anywhere on the internet!

Reply 391

Stryder402

is anyone else finding the legacy papers much more difficult lol

Reply 392

master_blaster66

Original post by katiecornish

No idea what the average raw mark conversion for 108ums is then? :frown:

cannot find them anywhere on the internet!

average for A* would be starting from 92

Reply 393

master_blaster66

Original post by Stryder402

is anyone else finding the legacy papers much more difficult lol

i think the legacy papers are much easier lol

Reply 394

Cleoleo

for 4c(iii)

What kind of diagram are we supposed to draw?

http://pdf.ocr.org.uk/download/pp_11_jan/ocr_61496_pp_11_jan_gce_f335.pdf?

Is it the whole catalysts hump, with catalyst, without, labelling H etc ?

(edited 11 years ago)

Reply 395

Cleoleo

Jan 11 was some tough paper -_-

Reply 396

Cleoleo

Original post by master_blaster66

i think the legacy papers are much easier lol

i thought so too!

Reply 397

kishenp

Original post by Beffnaay

Can anyone enlighten me on the nitrogen redox things? I thought I could do them but I found out that I really can't :frown:

What are you stuck on ?

Reply 398

kishenp

Could someone help me with this point of the spec on medicines by design
(a) describe and explain the structure and action of a given
pharmacologically active material in terms of:
(i) the pharmacophore and groups that modify it,
Thanks

Reply 399

Beffnaay