Aqa chem 4/ chem 5 june 2016 thread

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most +ve electrode potential means it's the best oxidising agent (itself is reduced).. Like I'm certain there..
One oxidises the other due to which is the higher electrode potential. More +ve electrode potential is reduced and oxidises the one with the lower electrode potential.
The reaction happens if the total electrode potential (more +ve - more -ve) is positive.

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My bad, I literally slipped right there LOL xD Yup, you are correct :h:

Reply 81

shiney101

For any calculation questions do you have to show the full working out that they used? Sometimes I'll show like a line or two and I'll get the answer right but would they give full marks for that even though I'd show every line that they've mentioned in the mark scheme?

Reply 82

Lilly1234567890

Why is a ammonia a stronger ligand in comparison to water?

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Reply 83

theboss1998

Original post by Lilly1234567890

Why is a ammonia a stronger ligand in comparison to water?

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Well, a ligand is a lewis base (electron donor). So i think that ammonia is a more basic than water (in terms of pH), and so it will be stronger as a ligand.

Reply 84

RMNDK

Original post by theboss1998

Well, a ligand is a lewis base (electron donor). So i think that ammonia is a more basic than water (in terms of pH), and so it will be stronger as a ligand.

You're not really answering the question. Why is it more basic? The more basic it is, the stronger the ligand so to answer the latter requires full explanation of the former.

Original post by Lilly1234567890

Why is a ammonia a stronger ligand in comparison to water?

Ligands are electron pair donors
If you can donate the lone pair of electrons to the metal ion more readily, you are going to form a stronger coordinate bond.
Nitrogen is less electronegative than oxygen so the lone pair of electrons is electrostatically attracted less to the nucleus. Thus it is more available to be accepted.

If I blu-tacced some money to a wall and superglued the same amount of money to another wall, which one is more obtainable? Same principle.

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Reply 85

cowie

Original post by RMNDK

You're not really answering the question. Why is it more basic? The more basic it is, the stronger the ligand so to answer the latter requires full explanation of the former.

Ligands are electron pair donors
If you can donate the lone pair of electrons to the metal ion more readily, you are going to form a stronger coordinate bond.
Nitrogen is less electronegative than oxygen so the lone pair of electrons is electrostatically attracted less to the nucleus. Thus it is more available to be accepted.

If I blu-tacced some money to a wall and superglued the same amount of money to another wall, which one is more obtainable? Same principle.

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I think ammonia is more polar than water as ammonia is NH3 and is trigonal pyramidal so it is more polar due to it having 3 inductive effects due to 3xH, than H2O which only has 2 inductive effects due to only 2xH?
And hence its electrons are more available as it is more polar?
- I may be wrong

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Reply 86

Guls

Original post by theboss1998

Well, a ligand is a lewis base (electron donor). So i think that ammonia is a more basic than water (in terms of pH), and so it will be stronger as a ligand.

its electron pair donor.

Reply 87

mortal infinity

For the nucleophilic addition reaction of aldehydes and ketones with HCN, does it need a dilute HCl catalyst? Also it it better to use KCN/NaCN since HCN is more toxic?

Reply 88

Superbubbles

is the rate equation and the rate expression the same thing?

Reply 89

SubwayLover1

Does one ethyl group have the same positive inductive effect as two methyl groups ? I can't find an answer :frown:

Reply 90

RMNDK

Original post by cowie

I don't think NH3 is more polar as the N-H bond will have a smaller dipole moment than the O-H bond. I'm also not so sure whether you can talk about hydrogen creating positive inductive effects, but even so, you can't compare as the central atom is different.
Yes there are more hydrogen atoms which release electrons, but oxygen will pull the electron density of the hydrogen atoms even more than nitrogen, and I don't know which is the bigger factor.

Reply 91

Superbubbles

does a catalyst affect the rate constant?

Reply 92

shiney101

Original post by Superbubbles

does a catalyst affect the rate constant?

No, only temperature will affect it

Reply 93

Superbubbles

does anyone know why in the condensation reaction 2n-1 water is produced

Reply 94

cowie

Anyone know the acid dissociation of H3PO4? - or what aqa want us to believe it is at least?

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Reply 95

JK11

Original post by shiney101

No, only temperature will affect it

You are wrong. you are thinking of Kc.

Reply 96

JK11

Original post by JacobFinney

If anyone can be arsed...Is it possible to run me through why there is a 3:5 ratio of manganate(VII): Iron(II) ethanedioate as opposed to the 2:5 ratio that I managed to get after cancelling out the electrons etc on June 2012 6(d)(i) ? I managed to get 4/5 for working through with my ratio but am a bit irritated at not being able to work out the right ratio.
http://filestore.aqa.org.uk/subjects/AQA-CHEM5-QP-JUN12.PDF
Ta

Iron ethanedioate releases 3 electrons. managnate releases 5.

Reply 97

SirRaza97

Original post by cowie

anyone know the acid dissociation of h3po4? - or what aqa want us to believe it is at least?

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h₃po₄-----> h₂po₄^-+ h⁺

Reply 98

shiney101

Original post by JK11

You are wrong. you are thinking of Kc.

Ahh yes! My bad, thanks for correcting me.

Reply 99

jammypancake

I don't really understand the difference in buffer calculation when there is XS base or XS acid?
What I usually do:
1. Find moles of each acid/base given
2. Find the XS mol of whatever is in XS
Am I right in thinking you use Ka for the acid XS buffer?
I always get the final answer wrong :frown:

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