Chemistry: Post your doubts here!

[Rizwan Javed]

How is A dehydration? :3

The products of the reaction are an alkene and water molecule. Since a water molecule is lost, the reaction is a dehydration reaction (or you can also say it to be an elimination reaction)

 

[synchros]

Hey guys! I want to know how to revise for As Level MCQs. I find Paper 2 relatively easy compared to Paper 1. So got any tips? Please share them and how to study for it.

 

[qwertypoiu]

Hey guys! I want to know how to revise for As Level MCQs. I find Paper 2 relatively easy compared to Paper 1. So got any tips? Please share them and how to study for it.

MCQs cover all topics so make sure you know the entire syllabus.
MCQs have to be completed within a very short amount of time so make sure you time yourself when doing the papers. Do it all in one go. Don't waste too much time on any one question. Leave difficult questions (like those involving complex calculations) for the end.
Practice many papers and read examiner reports for those that confuse you.
When you finish each paper evaluate yourself and see which topics make you lose the most marks. Revise these topics.
You can ask difficult questions here as well. Good luck

 

[Dark Destination]

The products of the reaction are an alkene and water molecule. Since a water molecule is lost, the reaction is a dehydration reaction (or you can also say it to be an elimination reaction)

Is this reaction mentioned in the Cambridge book?

 

[synchros]

MCQs cover all topics so make sure you know the entire syllabus.
MCQs have to be completed within a very short amount of time so make sure you time yourself when doing the papers. Do it all in one go. Don't waste too much time on any one question. Leave difficult questions (like those involving complex calculations) for the end.
Practice many papers and read examiner reports for those that confuse you.
When you finish each paper evaluate yourself and see which topics make you lose the most marks. Revise these topics.
You can ask difficult questions here as well. Good luck

Thank You!

 

[Rizwan Javed]

Is this reaction mentioned in the Cambridge book?

In the new edition, no. But instead of H3PO4, they have used Al2O3 catalyst for dehydration reactions.

 

[areeba240]

I don't have a calculator right now but the answer should be D I think.

Mr of CH4 is 16, which is much higher than that of H2 or He. So just look at the planet with largest amount of methane.

i didnt understand...can u plzz explain this qtn.....why there should more of methane

 

[qwertypoiu]

i didnt understand...can u plzz explain this qtn.....why there should more of methane

Because they want the densest material. And more dense means more mass. More methane is more mass. Right?

 

[areeba240]

Because they want the densest material. And more dense means more mass. More methane is more mass. Right?

yes....and how to find the mass from percentage by number of molecules.....
thank u for the help

 

[areeba240]

I don't have a calculator right now but the answer should be D I think.

Mr of CH4 is 16, which is much higher than that of H2 or He. So just look at the planet with largest amount of methane.

how to find the mass from percentage by number of molecules.....
thank u for the help

 

[fatimarehman]

Can someone help me with may June 2012 var 41,question 2,part bii onwards?

 

[cashew]

You have to play with the numbers to try to deduce the species responsible for each mass peak. Start with the smallest one and build on from there:

133 - SiCl3

I got this by subtracting various mass numbers from 133 on my calculator and this worked.

Next step is 149, which is 16 away, so just add O:

149 - SiCl3O

Next is 247... That's 98 we have to add. Cl2 gives 70, and Si another 28! So:

247 - Si2Cl5O

Then 263.... That's again a leap of 16:

263 - Si2Cl5O2

Next we have 396... 133 to jump! Get rid of 70 again with Cl2. 63 left. The last digit of 63 is 3, and that could be made by numbers ending with 8 and 5. Basically, 28 + 35 = 63. So we add SiCl3 more:

396 - Si3Cl8O2.

Hey, thanks a lot.
God Bless.

 

[The Sarcastic Retard]

Can someone help me with may June 2012 var 41,question 2,part bii onwards?

b(iii)

Spoiler: Add them up.

(iv) Rate determining step : The equation which contains reactants concentration in rate reaction. Its 2 or 3 here. H2 is involved plus O is formed from NO so step 2 has NO as well.

c(i) The last reaction has the highest Ecell value. So that reaction will go in forward direction and other two back ward, so NO is the answer.
(ii) dative or coordinate bonds when ligands will be attached to T.metal ion.
(iii) Like [Cu(NH3)4(H20)2]2+ it will be [Fe(NO)4(H20)2]2+

 

[fatimarehman]

Thanks. I had the same concept but how to write the equation for the overall reactions. Why the examiner has combined the equations 2 and 3? You missed that part.

 

[techgeek]

how to find the mass from percentage by number of molecules.....
thank u for the help

Multiply Mr by percentage
for A : (2 x 89.8) + (4 x 10.2) = 220.6
for B: (2 x 80) + (4 x 19) + (16x1) =252
for C: (2x 96.3) + (4 x 3.25) + (16 x 0.45) = 213.4
for D: (2 x 82.5) + (4 x 15.2) + (16 x 2.3) = 263.8
You could have guessed the answer straight away, since CH4 is the heaviest and it's largest percentage exists in D

 

[Eugene99]

Need a little help in equilibrium. The ICE table is kinda confusing to me... could somebody please explain how do I make one for this question?

 

[areeba240]

Multiply Mr by percentage
for A : (2 x 89.8) + (4 x 10.2) = 220.6
for B: (2 x 80) + (4 x 19) + (16x1) =252
for C: (2x 96.3) + (4 x 3.25) + (16 x 0.45) = 213.4
for D: (2 x 82.5) + (4 x 15.2) + (16 x 2.3) = 263.8
You could have guessed the answer straight away, since CH4 is the heaviest and it's largest percentage exists in D

thanks

 

[Rizwan Javed]

Need a little help in equilibrium. The ICE table is kinda confusing to me... could somebody please explain how do I make one for this question?
View attachment 60274

What's the answer? A?

 

[Eugene99]

What's the answer? A?

yep, it's A

 

[Abdullahassan_99]

Can someone explain how is the answer B?