Chemistry: Post your doubts here!

[shinnyyy]

With the kind of dp u hav
Calming down isnt possible

Lolx it's kasba xD
Ahhhh then I have tonne of phy questions and I'll make you to solve them

 

[Wkhan860]

Lolx it's kasba xD
Ahhhh then I have tonne of phy questions and I'll make you to solve them

Hahahahha
Ok

 

[tahakay]

If they ask you to draw the Structure of the organic compound , you draw structural formula or Displayed formula ? This question came in june 2015 p22 and i drew structural , will i lose all of the marks of that question because of it ?

 

[_MoHD_E]

If they ask you to draw the Structure of the organic compound , you draw structural formula or Displayed formula ? This question came in june 2015 p22 and i drew structural , will i lose all of the marks of that question because of it ?

In p21 they asked us for skeletal formula . If they ask you to draw the structure of the compound and they didn't mention either displayed or skeletal then don't worry boss you are 100% correct . Structural formula is therefore what they want

 

[tahakay]

Thankyou ! Im sorry to ask you this , but how do you know this ? Did some teacher told you or something ?

 

[_MoHD_E]

Thankyou ! Im sorry to ask you this , but how do you know this ? Did some teacher told you or something ?

Hey boss check oct nov 2005 paper 2 question number 5 F) and check the marking scheme the question also asked to draw the structure of the compound and in marking scheme a structural formula is given so don't worry boss

 

[tahakay]

Bro thankyou :') !

 

[_MoHD_E]

Bro thankyou :') !

Don't mention it boss

 

[phanttasy]

The thermal decomposition of Group 2 decreases down the group is due to the cation increases in size, and small cation with higher charge tend to undergo thermal decomposition with large anion. What would happened if both cation and anion are small in size too?

 

[Metanoia]

The thermal decomposition of Group 2 decreases down the group is due to the cation increases in size, and small cation with higher charge tend to undergo thermal decomposition with large anion. What would happened if both cation and anion are small in size too?

The variables are size of cation and size of anion, during comparison, keep one variable to be the same.

same size cation, increasing size of anion --> decomposition temperature decreases

increasing size of cation, same size anion --> decomposition temperature decreases

 

[Knightmare11]

http://imgur.com/iyav9gY

Why is the answer C? Thanks!

 

[_MoHD_E]

http://imgur.com/iyav9gY

Why is the answer C? Thanks!

first option is wrong because ethanol is having a minus charge which means it has donated its H+ to sulphuric acid and sulphuric acid is accepting the H+ this cannot be because concentrated sulphuric acid is a far stronger acid than ethanol therefore sulphuric acid is the acid which is going to lose its H+ to ethanol. ethanol is going to behave slightly like a base in this reaction. the stronger acid in the reaction is the acid which is going to lose the H+.

 

[Abdel Moniem]

View attachment 55508
why is it D. can someone explain

PCl5(g)-->PCl3(g)+Cl2(g)
Enthalpy Change=Enthalpy change of bonds broken+ Enthalpy change of bonds formed
2 P-Cl bonds were broken and a Cl-Cl bond was formed

 

[Michelle Ngu]

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?

 

[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