Chemistry: Post your doubts here!

[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

 

[The Sarcastic Retard]

i need help wid chem past papers solving

As or A2

 

[DipinS]

Anyone has topical past paers for AS level chemistry? Help me

 

[Copy Cat]

November 2002 Q6 (a)

 

[qwertypoiu]

November 2002 Q6 (a)

be specific. Which paper?

 

[qwertypoiu]

The shell of a chicken’s egg makes up 5% of the mass of an average egg. An average egg has a


mass of 50 g.

Assume the egg shell is pure calcium carbonate.

How many complete chicken’s egg shells would be needed to neutralise 50 cm3 of 2.0 mol dm–3

ethanoic acid?

So we are neutralising ethanoic acid using calcium carbonate:
2CH3COOH + CaCO3 --> (CH3COO)2Ca + H2O + CO2

Moles of ethanoic acid = 50/1000 * 2 = 0.1mol
Moles of CaCO3 required = 0.1/2 = 0.05mol
Mass of this CaCO3 = 0.05*Mr(CaCO3)= 5g

So we want 5g of eggshell.
Mass of average eggshell = 50g*5% = 2.5g
Number of eggshell required = 5/2.5 = 2 eggshells

Hope that was helpful

 

[AnonymousX9]

I don't understand the concept behind s,p,d sub-shells and orbitals and also the Aufbau principle. Can any please explain the basics?