Chemistry: Post your doubts here!

[iKhaled]

Waalikum Assalamu Wa Rahmatullahi Wa Barakatoho.

Well, for the cathode it worked perfectly.
Those cation which are less reactive than hydrogen (that is +ve E values) will form, as in Ag, while if not, then hydrogen forms.

Anion din't work with me either. But I always learned the when sulphate is there O2 is formed. Sorry. Rest I am confused too.

same thing happened to me PhyZac..worked with me perfectly with the cations but not with the anions :S:S

 

[ZainH]

Could anyone explain to me what reagents/conditions are used for elimination reactions, and why?
Thanks in advance.

 

[aleezay]

Two questions:
Q1. We write 'white fumes' as an observation if HCl is formed. Do we write the same thing for HBr and HI?
Q2. In reactions b/w PCl3 and alcohols/carboxylic acids heat is required, but not for those b/w them and PI3. Is this correct?
Also, does any one have Quick revision notes for Inorganic Chemistry? i just don't get it.. :/

 

[meobunny]

Ihow to make concentration for chemistry paper 5 rate of reaction, i need to vary concentration of HCL ! Please guide me urgent? Thanks

 

[knowitall10]

Ihow to make concentration for chemistry paper 5 rate of reaction, i need to vary concentration of HCL ! Please guide me urgent? Thanks

Which question is it?
Generally, to make any concentrations, we use serial dilution.. we add water to the given and make at least five concentrations. But in some mark schemes, they say "Reject/Ignore Serial dilution" so can you tell me which question you're talking about?

 

[PhyZac]

Anyone please explain!!! littlecloud11 PANDA-
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_22.pdf
Question 2 c i

How to know pH??

I made all as 7!

 

[PANDA-]

Aoa wr wb
need some detailed explanation on how to do qn 3 c of this paper pleaseeee

Using the method for electrode potential values, we don't get the answers exactly as the ms says

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_42.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_ms_42.pdf


PhyZac PANDA-
@everyone else taking A2

JazakAllah khair

Sorry, I'm AS still

 

[knowitall10]

actually i didnt get for the 1 d iv
cn u please explain it?didnt get the part thats written in the ms

Start the stopwatch as soon as you start adding HCl in the Na2S2O3. Stir with thermometer occasionally and stop the stop watch as soon as you no longer see the cross on the paper that's placed under the reaction vessel. BUT DON'T START TIMING AFTER MIXING OR STIRRING. time as soon you add the HCl.
This, I'm saying based on my knowledge of what we used to do in the AS practical. The problem I'm facing is that in the previous part, i don't know how to heat the reaction vessel. and, where to place the thermometer. I get the experiment but i just cant get the apparatus right. Can you please upload your diagram for that part?

 

[iKhaled]

According to the er:



It doesn't make sense. Like the anion which has the lowest electrode potential is the easiest to oxidise, right?

it is SUPPOSED to be a yes but i don't know i mean "we" don't know why the mark scheme is the opposite of us in this

 

[iKhaled]

this question needs a master in chemistry to fill the table and draw the graph. check question 2 ppl SOOO HARD!!!

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_53.pdf

 

[syed1995]

Anyone please explain!!!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_22.pdf
Question 2 c i

How to know pH??

I made all as 7!

Read the book.

1.) NaCl(s) + H2O --> NaCl(aq) .. no pH Change...
2.) MgCl2 + H2O --> only slightly hydrolyzes .. so pH 6.5 ..
3.) AlCl3 + 3H20 --> [Al(H2O)6]3+ and 3Cl-
[Al(H2O)6]3+ --> [Al(H2O)5(OH)]2+ and H+

so pH around 3..

 

[syed1995]

this question needs a master in chemistry to fill the table and draw the graph. check question 2 ppl SOOO HARD!!!

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_53.pdf

I am glad I am not in A2.

 

[ZainH]

Does no one know what reagents/conditions are used for elimination reactions, and why?

Asked it twice, no reply |:

 

[syed1995]

Does no one know what reagents/conditions are used for elimination reactions, and why?

Asked it twice, no reply |:

Reagent ..Na(OH) condition dipped in ethanol/heat under reflux .. for haloalkanes
Reagent .. Conc. H2SO4 /Al2O3 catalyst and 170C temperature.. for alcohols

 

[knowitall10]

Aoa wr wb
need some detailed explanation on how to do qn 3 c of this paper pleaseeee

Using the method for electrode potential values, we don't get the answers exactly as the ms says

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_42.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_ms_42.pdf


PhyZac PANDA-
@everyone else taking A2

JazakAllah khair

the question says aq. solutions of AgF, FeSO4 and MgBr2:
According to electrode potential values, the answer must be:
AgF
anode: O2
cathode: Ag
FeSO4 But when electrolysing FeSO4, why is SO2 wrong? beacause if you read pg 291 of
anode: SO2 x the chem textbook, you'll see that the OH- ions are discharged off at the anode
cathode: H2 in preference to sulfate ions. so the right answer is O2.

MgBr2 Same with MgBr2: on the same page, it also shows that Br- ions are discharged in preference to
anode: O2 x OH- ions so the right answer is Br2.
cathode: H2

 

[knowitall10]

using the other method that i showed u gives all of them correct values but i wonder why they dont give the same values with the potential electrodes if anyone here knows why or u know why then please do tell me because i want to know the reason now too..

look at pg. 291 of your textbooks and my reply to "Soldier..."

 

[xhizors]

column headings for winter 10 53 Q2
please any one
May Allah give you and me world wides distinctions Ameen

 

[ZainH]

Reagent ..Na(OH) condition dipped in ethanol/heat under reflux .. for haloalkanes
Reagent .. Conc. H2SO4 /Al2O3 catalyst and 170C temperature.. for alcohols

Thanks a ton, any specific reason why these reagents are chosen?

 

[syed1995]

Thanks a ton, any specific reason why these reagents are chosen?

Nope.. cuz it's written in the book and those are the only reactions which do elimination

 

[ZainH]

Nope.. cuz it's written in the book and those are the only reactions which do elimination

Ah I see, thanks again