Edexcel chemistry - unit 2 19th january 2012

Original post by pri_123

heyy guys i am resitting this unit too, anyone got a good way of revising the titrations?

To revise titrations I went through all the papers and did all the titration questions from each. Practise makes perfect and you'll start to notice the common things they'll ask in a certain order.

1. Often they ask an indicator first (for acid-base titrations this would be methyl orange or phenolphthalein, for iodine/thiosulphate titrations it would be starch).

2. Then they sometimes ask you to calculate the mean titre.

3. You would then calculate the moles of one of the reactants using the mean titre and the concentration given to you in the question.

For the rest of the titration question it'll be a case of using the equation for the ratios, and manipulating the equation concentration = moles/volume.

Reply 24

pri_123

Original post by Cetacea

To revise titrations I went through all the papers and did all the titration questions from each. Practise makes perfect and you'll start to notice the common things they'll ask in a certain order.

1. Often they ask an indicator first (for acid-base titrations this would be methyl orange or phenolphthalein, for iodine/thiosulphate titrations it would be starch).

2. Then they sometimes ask you to calculate the mean titre.

3. You would then calculate the moles of one of the reactants using the mean titre and the concentration given to you in the question.

For the rest of the titration question it'll be a case of using the equation for the ratios, and manipulating the equation concentration = moles/volume.

oh cool thank you :smile:

Reply 25

lets make this thread more active come ONNNNNNNNNNNN !!!! okay can someone temme definitions of electronegativity and why london dispersion forces !!

Reply 26

NutterFrutter

I'm ready for this exam, bring it on! :colone:

Reply 27

Original post by moizedexcel

lets make this thread more active come ONNNNNNNNNNNN !!!! okay can someone temme definitions of electronegativity and why london dispersion forces !!

Yes you're right - there's only 2 pages!

Electronegativity is the ability or tendency of an atom to attract the bonding pair of electrons to itself in a covalent bond.

London forces (aka dispersion forces or instantaneous dipole-induced dipole) exist between all molecules (both polar and non-polar ones). Chemguide explains their formation particularly well on this page.

Reply 28

Original post by Cetacea

Yes you're right - there's only 2 pages!

Electronegativity is the ability or tendency of an atom to attract the bonding pair of electrons to itself in a covalent bond.

London forces (aka dispersion forces or instantaneous dipole-induced dipole) exist between all molecules (both polar and non-polar ones). Chemguide explains their formation particularly well on this page.

well i noe how they r formed buh i wanna know a precise definition for the paper !! can i say that assymmetrical distribution of electrons results in an instantaneous dipole tht causes an induced dipoles in neighbouting atoms ...???

Reply 29

ok peeople can someoen write reaction when carbon dioxide passes thru the limewater...............also why prolonged passage of CO2 doesnt form a precipitate ok i noe hydrogencarbonate is soluble buh whats the reaction equation for this too

Reply 30

Original post by moizedexcel

well i noe how they r formed buh i wanna know a precise definition for the paper !! can i say that assymmetrical distribution of electrons results in an instantaneous dipole tht causes an induced dipoles in neighbouting atoms ...???

That's correct. It's unlikely you'll be asked to define London forces as such, but you will be expected to know their formation which is pretty much defining them! (June 2011 paper - 'Explain the formation of London forces').

Reply 31

Original post by Cetacea

That's correct. It's unlikely you'll be asked to define London forces as such, but you will be expected to know their formation which is pretty much defining them! (June 2011 paper - 'Explain the formation of London forces').

umm yeah !!! ok temme something about the exammm do you hve any paper or makr scheme tht u'd like to share our scho0o0ol duznt give nytihng !!!!!!!!!

Reply 32

aqua05

OP

9

oh God i feel so stressed for this paper :frown:

I dont know what to expect ?!
Anyone got tips on how to do good revision for this paper ??

Reply 33

cisne

6

Original post by aqua05

oh God i feel so stressed for this paper :frown:

I dont know what to expect ?!
Anyone got tips on how to do good revision for this paper ??

do pastpaper....again do it....again do it...well,im nervous too.......lets do our revision here..

Reply 34

Misslassenza

5

Original post by arnab

errm a bit confused....do we need to need about group2 stuff for unit1? just did the unit1 paper for june 2009 and there were some group2 question which i thought can only come up in unit2?

Also can someone help me understand this question :

Which of the following has the smallest ionic radius and WHY?

A. F-

B. Na+

C. Mg+2

D. O-2

The numbers refer to charge of each ion. The right answer is C but can someone give me a reason for it please?

As we go throught the periodic table from left to right the size of ions decreases
Mg2+ has the smallest ionic radius because it lost 2 electrons from its outermost shell and hence lost one energy level.

Na also lost one electron but comes before Mg2+ in the periodic table. In F- and O-2 they both gain electrons making their ionic radii higher than that of Mg2+

Reply 35

cisne

6

guys....do u hv any idea about wht might come up on this exam????

Reply 36

Original post by cisne

guys....do u hv any idea about wht might come up on this exam????

It's impossible to say really. I've just revised everything according to the syllabus as anything on there could come up again. I have made lots of notes and done as many practice questions as possible and because of this I feel much more prepared for this exam than I did in June last year, so hopefully that will reflect in my result.

Reply 37

This Honest

3

Can someone please explain to me what is the difference between induced dipole dipole and permanent dipole dipole?

Also, is induced dipole dipole the same thing as London forces and vdw forces?

I thought NH3 had london,permanent dipole and hydrogen bonding but my teacher told me it hasn't got permanent dipole dipole

:confused:

Reply 38