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OCR chem AS

Star_ice

did ne1 for chains and rings get 3 sumthing for the mass of the tablet? n what did u say the infra red spec. was showing?

i cant remember a question on a mass of a tablet!!

the infra red spec was showin a carboxylic acid i said

Reply 61

DavidnotMark

has any1 got the guide lines as to how many marks is an A,B,C etc... for foundation and mod 3 for the past few years? If someone has would they please mail them to me or pm me with them?

Reply 62

Star_ice

hellooooo

i cant remember a question on a mass of a tablet!!

the infra red spec was showin a carboxylic acid i said

oh sorry don't mean tablet- i mean the thing for removing stomach acid

Reply 63

DavidnotMark

i got 6.29g lol i bet its wrong :frown:

Reply 64

DavidnotMark

i know i got sum wrong lol i put Ti2Cl

Reply 65

Michael2005

Is that Foundation your talking about?- I don't remember a question on Stomach acid in chains and rings..., and also, what other questions were there on alcohols, because i remember feeling that they went really well when i did them, but i cant remember any apart form the infra red spec question!

Reply 66

Aired

1

Are you talking about the indigestion tablets in the practical plan Star Ice? :s-smilie:

The only alcohol question was reaction with a carboxylic acid to give an ester, and the infa-red spectroscopy I think.

Reply 67

Star_ice

yeh sorry- i was talking about the infra red spec. and the other 1 mite hav bin in foundation but it was about stomach acid, and whether he had taken enough of magnesium- or sumthing lyk that.

don't worry, probably confused u even more.

Reply 68

Aired

1

Star_ice

did ne1 for chains and rings get 3 sumthing for the mass of the tablet? n what did u say the infra red spec. was showing?

The spectrum was showing the carboxylic acid because it had a broad O-H peak.

Reply 69

Untitled

There was a question on Milk of Magnesia for neutralising stomach acid, it told you how much Mg(OH)₂ they had taken and asked if it was too much too little or just right for the amount of acid present. Think i came up with not enough but i cant remember. The last question threw me, does anyone know why the atomic radius of Nitrogen is bigger than Oxygen?

Reply 70

Star_ice

yeh thats the question!
erm. for the last question i jst wrote about how it had more protons, so then the charge was bigger so it attrated the electron shells closer. but i 2 was really stuck on that question.

Reply 71

Untitled

Yer i started ritin that but realised they both had the same charge density, technically oxygen shuould be bigger than nitrogen as its further across the period so there must be some anomolous explanation. Tried explaining it in terms of electron structure, electron electron repulsion in oxygens 1st p orbital reduces ionisation energy but struggled to link that to atomic radius.

Reply 72

DJ Shadow

Its because Oxygen possesses a half-full shell which makes it more stable and hence stronger attractive forces between the nucleus and electrons. Therefore stronger forces pulls the the atom together more tightly.

The electronic configuration of oxygen is 1s2,2s2,2p4 (4 away from being full-a half full shell)

The electronic configuration of Nitrogen is 1s2, 2s2, 2p3 (5 away from a full shell so less stable)

This is all based on spin-pair repulsion theory

This is what i put in the exam anyway, so I'm probably wrong

Reply 73

Talya

16

DJ Shadow

Its because Oxygen possesses a half-full shell which makes it more stable and hence stronger attractive forces between the nucleus and electrons. Therefore stronger forces pulls the the atom together more tightly.

The electronic configuration of oxygen is 1s2,2s2,2p4 (4 away from being full-a half full shell)

The electronic configuration of Nitrogen is 1s2, 2s2, 2p3 (5 away from a full shell so less stable)

This is all based on spin-pair repulsion theory

This is what i put in the exam anyway, so I'm probably wrong

That's way too complicated for 2 marks :biggrin:

-Kavanne

Reply 74

DJ Shadow

Im sure it was more than 2 marks, about 3 or 4 weren't it? There was about half a page dedicated to the question

Reply 75

Untitled

Yer it was 4 marks. What did everyone put for the other 4 marker, bond angle in NH3 i think it was? 107.5 cos there were 4 pairs of electrons surrounding the central atom an 1 was a lone pair which repel more. Any ideas on what the fourth mark was for?

Reply 76

rachaelt

Untitled

Yer it was 4 marks. What did everyone put for the other 4 marker, bond angle in NH3 i think it was? 107.5 cos there were 4 pairs of electrons surrounding the central atom an 1 was a lone pair which repel more. Any ideas on what the fourth mark was for?

I also put that the lone pair reduces the bond angle by 2.5 but not sure if thats worth a mark!

Reply 77

stratomaster

Untitled

Yer it was 4 marks. What did everyone put for the other 4 marker, bond angle in NH3 i think it was? 107.5 cos there were 4 pairs of electrons surrounding the central atom an 1 was a lone pair which repel more. Any ideas on what the fourth mark was for?

Are we talking about the module 1 exam here? foundation chemistry?

The angle is 107° .. it's a pyramidal molecule because there are 3 bonded pairs and 1 lone pair. I talked about electron repulsion theory where the lone pair push more than the bonded pairs and so reduce the bond angle.

Reply 78

stratomaster

Untitled

Yer i started ritin that but realised they both had the same charge density, technically oxygen shuould be bigger than nitrogen as its further across the period so there must be some anomolous explanation. Tried explaining it in terms of electron structure, electron electron repulsion in oxygens 1st p orbital reduces ionisation energy but struggled to link that to atomic radius.

Nah, oxygen should be smaller than nitrogen. It's further across period 2 and there is 1 extra proton, so there is increased nuclear charge and the same shielding. Also there is 1 extra electron so the nuclear attraction increases and the shell is attracted inwards more so the atomic radius decreases.