ocr a f325 revision thread

Scroll to see replies

Reply 2640

kuku2013

Original post by scorpio22

i meant 2013 january ...

1ii

welcome back to reality

Reply 2641

_HabibaH_

Original post by MedMed12

what do you mean went down? had you sat the paper before this Jan?
hopefully we'll be OK. Guessing you need an A for chemchem?

Yes I'm on a gap year, resitting. I managed the A in biology 4 & 5 but went down from B grades in chem 4 & 5 - so I'm taking them AGAAAAIN for an A.

Reply 2642

Myocardium

Original post by bmpink

The position of equilibrium changes because the concentrations of the reactants change, because if there's more on one side and less on the other... ! Sorry yes it does, force of habit! My teacher ALWAYS wrote it like that haha.

Ah right - thanks!

Reply 2643

otrivine

Original post by kevloui

Ok let me warm you guys up..

Construct the equation for the oxidation of acidified iron(II) ions by oxygen

4Fe2+ + 4H+ + O2 ----> 4Fe3+ + 2h2o

Reply 2644

kevloui

Original post by otrivine

4Fe2+ + 4H+ + O2 ----> 4Fe3+ + 2h2o

Yep;
What do you understand by the term bidentate ligand?

Reply 2645

_HabibaH_

Original post by Myocardium

Do we need to know the half equations for hydrogen oxygen fuel alkaline cells?

They gave it in the table didn't they? The important thing is to pick according to the conditions - I overlooked it though it was written clearly in bold.

Reply 2646

Myocardium

Original post by _HabibaH_

Yes I'm on a gap year, resitting. I managed the A in biology 4 & 5 but went down from B grades in chem 4 & 5 - so I'm taking them AGAAAAIN for an A.

What grade did you get for chem 4 and 5 first time round if you don't mind me asking? :smile:

Was it a really difficult paper?

Reply 2647

kuku2013

Original post by kevloui

Yep;
What do you understand by the term bidentate ligand?

wait wait wait what was answer to the other question the one about describe a test.....

Reply 2648

JimmyA*

Original post by bmpink

4 moles of iron!? Where?! But do you just balance the four with 4Fe2+ and 4Fe3+?

Yes it's because you first write the 2 half equations:
Fe2+ ----> Fe3+ + e-
O2+ 4H+ + 4e- ----> 2H2O and then do the full equation

Reply 2649

AFC_123456789

In platin, what is the coordination number

Reply 2650

otrivine

Original post by kevloui

Yep;
What do you understand by the term bidentate ligand?

A molecule or ion that can donate 2 lone pair of electrons to a transition metal ion forming 2 coordinate bonds

Reply 2651

liam627

Original post by kevloui

Yep;
What do you understand by the term bidentate ligand?

A bidentate ligand, is an ion/molecule that can donate two pair of electrons to a central metal ion forming TWO coordinate bonds.

How is a buffer solution created and explain how it minimises changes to pH.

Reply 2652

otrivine

Original post by AFC_123456789

In platin, what is the coordination number

4 coordinate bonds

Reply 2653

kevloui

Original post by kuku2013

wait wait wait what was answer to the other question the one about describe a test.....

lol I wouldn't worry too much about it, but there's no reason why it wouldn't be a 1 marker:
Add (aqueous) sodium hydroxide which will give a brown/rusty ppt

Reply 2654

Myocardium

Original post by _HabibaH_

They gave it in the table didn't they? The important thing is to pick according to the conditions - I overlooked it though it was written clearly in bold.

Haha they always throw in a dodgy equation in those tables to throw us off, like those ones where two similar half eqs have the same species, and only when you are halfway through merging two equations together you realize that you overlooked the other one -_-

Reply 2655

Nuna

Original post by rival_

In the mark scheme where does the "40" come from when working out conc^ in g dm^-3

this

Reply 2656

Dr00n

Original post by kevloui

niiiiiiceee; although its 4 moles of the iron, but nonetheless..
Describe a test to show the presence of iron(III) ions in a solution of FeSO4.7H2O.

Do you add NaOH to it to get a brown ppt?

Reply 2657

kevloui

Original post by otrivine

A molecule or ion that can donate 2 lone pair of electrons to a transition metal ion forming 2 coordinate bonds

Original post by liam627

Yup, Explain why the H—O—H bond angle in the water ligand is 107° rather than 104.5°.

Reply 2658

überambitious_ox

Original post by bmpink

Haha i've found it! For the Zn half cell, you need 2 electrons to balance the charge, and bottom you need 2Cr2+ to balance the 2 cr on the left, 7h2o on right to balance the O7 in the dichromate and 14H+ on the left to balance the 7x2 H's on the right! :smile: