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

Can someone explain how to work out the ratio of salt/acid in a solution?
or give an example of a question and show working.

Reply 101

matt1107

What is the difference between dissociation and ionising. The revision guide says "a strong acid ionises fully", and the book also says "weak acids dont ionise fully", but later states " only small amounts of the acid dissociate?

Reply 102

navarre

20

Original post by matt1107

What is the difference between dissociation and ionising. The revision guide says "a strong acid ionises fully", and the book also says "weak acids dont ionise fully", but later states " only small amounts of the acid dissociate?

They're the same thing. You can talk about an acid losing its H+ ions in terms of ionisation or dissociation.

Reply 103

master_blaster66

17

how do you decide which bit is the phramacophore of a structure?...so confused

Reply 104

Bi0logical

7

Original post by master_blaster66

how do you decide which bit is the phramacophore of a structure?...so confused

Well, they show you two molecules usually, and you look at a structure which they both have, then you circle that structure because it's same in both. It's usually the pharmacophore, this produces the activity/biological response in the body

Reply 105

master_blaster66

17

Original post by Bi0logical

Well, they show you two molecules usually, and you look at a structure which they both have, then you circle that structure because it's same in both. It's usually the pharmacophore, this produces the activity/biological response in the body

thanks

would the same count for chromophore too?

Reply 106

hash007

15

I'm being lazy but, would help if anyone had a list of all the reactions + conditions we had to learn?

Cheers!

Reply 107

master_blaster66

17

Original post by hash007

I'm being lazy but, would help if anyone had a list of all the reactions + conditions we had to learn?

Cheers!

lol theres tooo many to list down..theyre all on the revision guide and on the text book

Reply 108

Bi0logical

7

Original post by master_blaster66

thanks

would the same count for chromophore too?

They wont ask like that about the chromophore.

But probably say what makes azo dyes colored? A: Chromophore

IF they ask us to circle a chromophore, its just the delocalised system, so just circle both benzene rings and N=N bond. Electrons in the delocalised system need less energy to become excited than those with covalent bonds, this energy is available when molecule absorbs visible light.

Reply 109

sunshinesmile10

Original post by Bi0logical

Can someone explain how to work out the ratio of salt/acid in a solution?
or give an example of a question and show working.

you need to use the equilibrium constant equation.. so if you rearrange it, then you get the ratio as Ka/H = A-/ HA (which is the ratio)
so basically you divide Ka(which is given) by H ... the number you get is the ratio and just correspond it to 1 to make the ratio.

Reply 110

hash007

15

Can anyone quickly explain atomic emission/absorbtion spectrum. It's synoptic and has popped up in a few past papers and I can't remember a thing :redface:

Reply 111

Bi0logical

7

Original post by sunshinesmile10

you need to use the equilibrium constant equation.. so if you rearrange it, then you get the ratio as Ka/H = A-/ HA (which is the ratio)
so basically you divide Ka(which is given) by H ... the number you get is the ratio and just correspond it to 1 to make the ratio.

So is that always the technique when asked about ratio of acid/salt?
I'm probably going to get all the calculations wrong in this paper :frown:

Reply 112

sunshinesmile10

Original post by Bi0logical

So is that always the technique when asked about ratio of acid/salt?
I'm probably going to get all the calculations wrong in this paper :frown:

just to clarify.. this is the ratio of salt (A-) over acid (HA) not acid over salt. But this is the one they usually ask...
In terms of calculations, dont stress out. Do lots of paper questions and make sure you UNDERSTAND whats happening rather then just learning it up. I know its easy to say and all but knowing salters they love to throw a little curveball
.....think how good you'll feel when you can say goodbye to chemical ideas :P :P

Reply 113

sunshinesmile10

2 questions - firstly does anyone have a past paper for jan 2010
also, how do we balance the equations using electrons... is there notes anywhere, i cant find them.. thanks

Reply 114

-James-

Suggest an equation for the reaction of sulfur tetrafluoride with oxygen to form sulfur
hexafluoride.

Ans: SF4 + 02 ---> SF6 + S02

How the hell do you know S02 is produced when it doesn't say it in the Q!

This is F335, Jun 2011 q.