Chemistry: Post your doubts here!

[Abdel Moniem]

on being heated the hydrogen iodide breaks down more quickly than hydrogen chloride.Which statement explains this faster rate?
1 HI bond is weaker than HCl bond
2 the reaction of breakdown of HI has a smaller activation energy than HCl
3 breakdown of HI is more exothermic than HCl
Why is 2 acceptable & why not 3 too?

2 is acceptable because the overlap of the orbital of the H and I atoms produces a longer bond length thus bond strength is lower. Less energy is then required to break the H--I bond. 3 is incorrect because any decomposition requires the input of energy(endo).

 

[Metanoia]

on being heated the hydrogen iodide breaks down more quickly than hydrogen chloride.Which statement explains this faster rate?
1 HI bond is weaker than HCl bond
2 the reaction of breakdown of HI has a smaller activation energy than HCl
3 breakdown of HI is more exothermic than HCl
Why is 2 acceptable & why not 3 too?

There are 2 stages in the reaction
STAGE 1: the breaking of the H-X bonds
STAGE 2: forming of the H-H and X-X bonds.

The rate is limited by how easy STAGE 1 (breaking of the H-X) occurs.

Statement 1 and 2 is related to the weakness of the H-X bonds (STAGE 1)

Statement 3 takes about the combination of the two stages without being specific about STAGE 1.

 

[nehaoscar]

Is Mg(OH)2 more soluble in MgSO4 or in H2O?
The answer is H2O
And it says that MgSO4 has a common ion so it reduces the solubility but H2O also has a common ion (OH-) ... :/
Can someone please explain??
http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w07_qp_4.pdf
Q2 c - ii

 

[Metanoia]

MgSO4 breaks up into Mg2+ and sulfate ions readily

Water however, dissociates to OH- and H+ to a small extent (1 x 10-7 mol/dm3).

So if the impact of the OH- ion as the "common ion" is insignificant compared to the Mg2+ ions.

 

[peacce]

dear all,
i need a suggestion and hope that u guys will suggest me the best,
i've got really unexpected result c in maths and d in chem and physics
i'm planning to appear for AS PHY this november and appear for chem accelerated in may/june 2016 as my teacher suggested so, before i appear for chemistry im going to get my papers rechecked because i dont think i can get less than an A.
plz give me your suggestion in this matter... SHOULD I APPEAR FOR PHY IN NOV OR NOT?
P.S. i was expecting STRAIGHT A's

 

[nehaoscar]

dear all,
i need a suggestion and hope that u guys will suggest me the best,
i've got really unexpected result c in maths and d in chem and physics
i'm planning to appear for AS PHY this november and appear for chem accelerated in may/june 2016 as my teacher suggested so, before i appear for chemistry im going to get my papers rechecked because i dont think i can get less than an A.
plz give me your suggestion in this matter... SHOULD I APPEAR FOR PHY IN NOV OR NOT?
P.S. i was expecting STRAIGHT A's

http://gceguide.com/papers/A Levels/Physics (9702)/
Check out the m/j/15 paper and mark scheme and try to compare the mark scheme with the answers you remember you wrote
You can thus calculate an approximate score which you think you should have and so decide whether to re-check or re-sit the physics

 

[Copy Cat]

9701/02/O/N/04
Q 5 (c) part

 

[Metanoia]

9701/02/O/N/04
Q 5 (c) part
View attachment 55724

C2H4O --> C3H6O3

moles of ethanal used = 4.4/44 = 0.1 mol
moles of lactic acid expected = 0.1 mol
mass of lactic acid expected = 0.1 x 90 = 9 g

% yield of lactic acid = actual mass/expected mass x 100% = 5.4/9 x 100% = 60%

 

[Adnan Nurani]

why isnt chemguide.co.uk not opening? Is there any good website to study chemistry?

 

[The Sarcastic Retard]

why isnt chemguide.co.uk not opening? Is there any good website to study chemistry?

Go to google, type chemguide and open the link where u find chemguide.co.uk
It is still working.

 

[qwertypoiu]

why isnt chemguide.co.uk not opening? Is there any good website to study chemistry?

Try http://www.chemguideforcie.co.uk

 

[bubbles1997]

Aoa everyone. Can somebody please guide me to A2 topical worksheets? I mean question papers? It is difficult to check for a specific chapter in every paper.

 

[qwertypoiu]

Aoa everyone. Can somebody please guide me to A2 topical worksheets? I mean question papers? It is difficult to check for a specific chapter in every paper.

Try here:
https://www.xtremepapers.com/community/threads/a2-chemistry-topicals-here.30502/

 

[bubbles1997]

Try here:
https://www.xtremepapers.com/community/threads/a2-chemistry-topicals-here.30502/

thank you. They were really helpful. God bless

 

[omar999]

guys does anyone know where can I find june 2015 mark schemes for AL Chemistry ?? Thanks in advance.

 

[_MoHD_E]

guys does anyone know where can I find june 2015 mark schemes for AL Chemistry ?? Thanks in advance.

http://gceguide.com/papers/A Levels/Chemistry (9701)/

 

[Xtreamer]

2 is acceptable because the overlap of the orbital of the H and I atoms produces a longer bond length thus bond strength is lower. Less energy is then required to break the H--I bond. 3 is incorrect because any decomposition requires the input of energy(endo).

1 is correct too right? And why do H and I atoms produce a longer bond?

 

[qwertypoiu]

1 is correct too right? And why do H and I atoms produce a longer bond?

Yes, 1 is correct.
HI forms longer bonds than HCl, because the valence electron of Iodine is much further away from the nucleus than the valence electron of Chlorine.
Longer bonds are weaker, simply because the nuclei of the atoms forming the bond are far away from the shared electron pair, and thus have weaker attraction to it, and so can be easily broken.
Hope that made sense

 

[Xtreamer]

Yes, 1 is correct.
HI forms longer bonds than HCl, because the valence electron of Iodine is much further away from the nucleus than the valence electron of Chlorine.
Longer bonds are weaker, simply because the nuclei of the atoms forming the bond are far away from the shared electron pair, and thus have weaker attraction to it, and so can be easily broken.
Hope that made sense

Yeah it Did THANKS =)

 

[22shimmer22girly]

i need help wid chem past papers solving