Edexcel chemistry - unit 2 19th january 2012

Original post by Cetacea

Spot on! For (c) though just remember to say 'heat with alcoholic NH₃ in a sealed tube or container' to avoid contact with air.

aite klkl.....can u try and explain i put up on last post plzzzzzzzzzzzzzzzzzzz???

and here is another question for u, draw a diagram to show how u can do each of those experiment and label all the appratus!

Reply 142

F1's Finest

21

i got a question. explain why thermal stability of nitrates and carbonates increases down the group.

Reply 143

Original post by James A

i got a question. explain why thermal stability of nitrates and carbonates increases down the group.

As you are going down the group, the radius of the M2+ cation increases but the charge stays the same, hence the charge density decreases, Therefore the M2+ cation becomes less polarising towards the anion, hence less covalent and more ionic. This means the electrostatic attraction between the nitrate and the M2+ cation gets stronger, hence more energy is needed to overcome it.
therefore the thermal stabilty of it increases.

This might not be right cos again, i m doing this from the top of my head.

Reply 144

F1's Finest

21

Original post by arnab

As you are going down the group, the radius of the M2+ cation increases but the charge stays the same, hence the charge density decreases, Therefore the M2+ cation becomes less polarising towards the anion, hence less covalent and more ionic. This means the electrostatic attraction between the nitrate and the M2+ cation gets stronger, hence more energy is needed to overcome it.
therefore the thermal stabilty of it increases.

This might not be right cos again, i m doing this from the top of my head.

correct...... ring ring ring!!

Reply 145

halaaa

Is it true that polar molecules act as green house gases
If so then y do co2 and methane which are not polar called as such ?

Reply 146

Cetacea

8

Original post by halaaa

Is it true that polar molecules act as green house gases
If so then y do co2 and methane which are not polar called as such ?

Any molecule that changes its dipole moment when it absorbs infrared radiation can behave as a greenhouse gas. That means that even if the molecule is not polar but has polar bonds, like methane and carbon dioxide, the molecule can absorb infrared radiation and behave as a greenhouse gas.

Obviously water vapour, which has polar bonds and is itself polar, is a potent greenhouse gas.

Reply 147

This Honest

3

Hey guys,

In the syllabus, 2.7c part 3.
It tels us that we need to know the reaction between hydrogen halides with ammonia and with water to produce acids.

I haven't done this nor can i find it in the book?
any help?

edit: woops, i know the ammonia part NH3 + HCL --> NH4CL :colondollar:

but the water part, im still puzzled

edit 2: is it HCL + H20--> H3O+ + CL^-???

(edited 12 years ago)

Reply 148

so wt experiment do u lot think is going to come up that we will most likley have to draw?

Reply 149

041087

2

i have 2 mc to ask
http://www.sendspace.com/file/3k5uuz

Q11 why is A not C?
Q13 why is D not B?

(edited 12 years ago)

Reply 150

elprince_ra

Original post by 041087

i have 2 mc to ask
http://www.sendspace.com/file/3k5uuz

Q11 why is A not C?
Q13 why is D not B?

do u remember that part in the book which said : "STRAIGHT CHAINS HAVE STRONGER LONDON FORCES THAN BRANCHED CHAINS"........... so in the question he has made it easy for u by saying it depends on the strength of London Forces

for Q13 : as the conc. increases .......... position of equilibrium moves to the side with fewer no. of molecules..................... and as the conc. increases the rate of reaction increases

this is the case in the question ..... as he added more Ag+ the position of equilibrium moves to the right so as a result Ag (s) & Fe3+ increases ............ besides the rate of reaction increases to as there have been more no. of molecules per unit volume.. so more collisions are successful

hope u got the point

Reply 151

OP

Helloo can anyone help me answering this question from may 2011 Q19f) why is the answer Z & not X ?? :s-smilie:

Thank you in advance :smile:

Reply 152

halaaa

How to measure the residual alkali from skinning fruit with potassium hydroxide?
It is in da syllabus

Reply 153

BeHappy

Original post by aqua05

Helloo can anyone help me answering this question from may 2011 Q19f) why is the answer Z & not X ?? :s-smilie:

Thank you in advance :smile:

Hi, this one confused me too :smile:

It's because you have one +/- 0.05 error for initial reading and one for the final reading, so it's +/- 0.1

Reply 154

Original post by amy7

hi, this one confused me too :smile:

it's because you have one +/- 0.05 error for initial reading and one for the final reading, so it's +/- 0.1

thank you!

Reply 155

OP

Original post by Amy7

Hi, this one confused me too :smile:

It's because you have one +/- 0.05 error for initial reading and one for the final reading, so it's +/- 0.1

i dont understand :frown:

Reply 156

OP

you guys are just doing the new syllabus papers or you guys doing some other papers as well ?

Reply 157

Cetacea

8

Original post by aqua05

you guys are just doing the new syllabus papers or you guys doing some other papers as well ?

I'm mainly sticking to the new syllabus papers but have also done a few questions from the AQA Unit 2 papers as a lot of the content overlaps. It's good just to get extra practice and see questions presented to you in a different way.

So how do you feel about the exam? Less than 48 hours away now!

Reply 158

OP