AQA CHEM5 A2 Chemistry - 19th June 2013

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Reply 1900

Brightbud

Original post by marleyxd

Then why do ionic lattices with covalent character have higher (more negative) latice formation enthalpies?

they don't

Reply 1901

Kaii_Smith

Original post by rommy123

can someone please explain the perfect ionic model?

Ions are perfect spheres and it has no covalent character :smile:

Reply 1902

RoaringLion

Original post by rommy123

can someone please explain the perfect ionic model?

The perfect ionic model states:

All ions exist as perfect spheres
AND
There are forces of electrostatic attraction between ions.

This would be worth 2 marks ma if it were to appear, that's the answer, hope it helps.

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Reply 1903

MrMeep2580

Original post by rommy123

can someone please explain the perfect ionic model?

Basically it incinuates that all ions are perfect spheres with no distortion or covalent character so assumes they are purely ionic

Reply 1904

gooner1886

Could someone please explain what the mark scheme means in question 6c, Jun 10? (http://filestore.aqa.org.uk/subjects/AQA-CHEM5-W-MS-JUN10.PDF)

"(Delta S is negative so) at high tempt - T Delta S (is positive and) greater than Delta H

So Delta G > 0"

The actual calculation is easy but the above carries two marks

Reply 1905

Med_me

Is the positive terminal of a cell the anode or the cathode?

Reply 1906

Brightbud

Original post by BerryB

But it says excess ammonia. So shouldnt it form:
[Al(NH2CH2CH2NH2)3]

its not in excess

Reply 1907

DELETED ACCOUNT

Original post by BerryB

But it says excess ammonia. So shouldnt it form:
[Al(NH2CH2CH2NH2)3]

No. That would be an example of ligand substution. Ligand subsitution reactions can only occur with copper, chromium and cobalt.

Reply 1908

RoaringLion

Original post by Med_me

Is the positive terminal of a cell the anode or the cathode?

Anode is positive, cathode is negative.

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Reply 1909

zaha.k

hey.. can someone post the markscheme for the jan 13 chem 5?

Reply 1910

MrMeep2580

Original post by Med_me

Is the positive terminal of a cell the anode or the cathode?

anode

Reply 1911

Med_me

Original post by RoaringLion

Anode is positive, cathode is negative.

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Thanks!

Reply 1912

Med_me

Original post by MrMeep2580

anode

Thanks, and is the oxidising agent found there?

Reply 1913

BerryB

Original post by frogs r everywhere

No. That would be an example of ligand substution. Ligand subsitution reactions can only occur with copper, chromium and cobalt.

Ohhh ok. thanks i get it now!!

Reply 1914

marleyxd

Original post by Brightbud

they don't

Yes they do lol.... read p174 of nelson thorne

Reply 1915

AspiringGenius

Original post by frogs r everywhere

No. That would be an example of ligand substution. Ligand subsitution reactions can only occur with copper, chromium and cobalt.

what, I didn't know this, why is that?

Reply 1916

Bootala

do we need to know how to work out Back Titrations?

Reply 1917

Emfasis

Original post by popnit

I know but I can't figure out why you put 2 moles!

To balance the charge :smile:

Reply 1918

AspiringGenius

Partial covalent character in an ionic lattic increases the lattice dissociation enthalpy. i.e. it takes more energy to break up the lattice.

Why then, does Al2O3's partial covalent character make it have a lower melting point than MgO?