Chemistry: Post your doubts here!

[LeoMessi]

Hahahh. This is one of my better drawings

Always sucked at drawings and diagrams and always will. This is why I loathe P5. All my diagrams are so funny it's actually amusing lol

Abby can you OR ANYONE plss explain the question to me???? The answer is also attached
plsss
ANSWER

 

[GCE As and a level]

https://www.xtremepapers.com/community/threads/chemistry-p21-gt.33403/

GUYS VOTE HERE ABOUT YOUR EXPECTATIONS FOR CHEMISTRY ''GT'' P21
________________________________________________________________________
https://www.xtremepapers.com/community/threads/biology-9700-p11-gt.33482/

GUYS VOTE HERE ABOUT YOUR EXPECTATIONS FOR BIOLOGY ''GT'' P11
________________________________________________________________________

BEST OF LUCK

 

[A star]

https://www.xtremepapers.com/community/threads/new-format-of-exams-for-2014.33380/page-2#post-773505

 

[Dexterwarrior12]

2 Questions. Firstly, in p4 (A2), do we have to memorize the colour of complexes of all transition metals? Apart from Co and Fe ones ofcourse.
Secondly, what about when we add KMno4 to Fe2+ solution? TEchnically, shouldn't the solution turn from green to brown? Mark scheme says that the solution turns colourless and then finally on excess of MnO4- it turns pink. How?

 

[Farez]

Abby can you OR ANYONE plss explain the question to me???? The answer is also attached
plsss View attachment 41708
ANSWER View attachment 41708View attachment 41709

Have you read the chapter on partition coefficients? This page does a great job in explaining the concept and how to do the calculations. http://www.chemguide.co.uk/CIE/section112/learningf.html

Read that page and try to figure out how to solve the question yourself. It's mostly math anyway.

2 Questions. Firstly, in p4 (A2), do we have to memorize the
of complexes of all transition metals? Apart from Co and Fe ones ofcourse.
Secondly, what about when we add KMno4 to Fe2+ solution? TEchnically, shouldn't the solution turn from green to brown? Mark scheme says that the solution turns colourless and then finally on excess of MnO4- it turns pink. How?

No need to memorize colours of complexes, other than Cu2+ complexes, and iron (ii)/(iii) ones. Make sure you know the reason behind the colours as that is a very common question.

As for your second question, it's rather subjective. The colour of the Fe2+ solution really depends on the concentration of the ions. If it's dilute, the colour would be harder to notice than the very prominent purple of the KMnO4 solution. This is what I think to make the most sense. I have no idea what the examiner had in mind lol.

 

[Someone2]

can anyone explain if cyclohexane reacts with NaOH or not?? so confused...

 

[Farez]

can anyone explain if cyclohexane reacts with NaOH or not?? so confused...

Cyclohexane is an unsaturated organic compound so it wouldn't react with NaOH.

Phenol does react with NaOH, as phenol is acidic (lone pair of O being delocalised into the ring causes the O-H bond to be more polar so the H breaks off more easily)

 

[Shkrrhmt]

can teach me steps to sketch graph for acid-base neutralisation? for eg: 25 cm^3 of 0.200moldm^-3 NaOH is titrated against 0.100 moldm^-3 ethanoic acid solution. Tq

 

[Farez]

can teach me steps to sketch graph for acid-base neutralisation? for eg: 25 cm^3 of 0.200moldm^-3 NaOH is titrated against 0.100 moldm^-3 ethanoic acid solution. Tq

This page does a great job in thoroughly explaining it http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html

Make sure you understand acid-base reactions, pH calculations, and buffer solutions first though.

 

[AnujaK]

Hi everyone
I've started a site which will provide you with solved papers showing all the steps in the working and with useful tips on the side. The best part is that when you look at a solved paper, you can look at commonly made mistakes and learn from them.
Please do check it out!
https://sites.google.com/site/fromatoscom/home

 

[A star]

can anyone explain if cyclohexane reacts with NaOH or not?? so confused...

NaOH doesnt react with cyclohexane nor cyclohexene it reacts with phenols forming sodium phenoxide

 

[Dexterwarrior12]

Have you read the chapter on partition coefficients? This page does a great job in explaining the concept and how to do the calculations. http://www.chemguide.co.uk/CIE/section112/learningf.html

Read that page and try to figure out how to solve the question yourself. It's mostly math anyway.



No need to memorize colours of complexes, other than Cu2+ complexes, and iron (ii)/(iii) ones. Make sure you know the reason behind the colours as that is a very common question.

As for your second question, it's rather subjective. The colour of the Fe2+ solution really depends on the concentration of the ions. If it's dilute, the colour would be harder to notice than the very prominent purple of the KMnO4 solution. This is what I think to make the most sense. I have no idea what the examiner had in mind lol.

thanks man, thanks alot

 

[A star]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_41.pdf 5d(i)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_ms_41.pdf is the answer correct , i mean is the water molecule sttracted towards Na in this way???

 

[Dexterwarrior12]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_41.pdf 5d(i)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_ms_41.pdf is the answer correct , i mean is the water molecule sttracted towards Na in this way???

I found that confusing too, but I don't think its important, because they gave marks without the mention of that point too, anyways, hoping that someone will answer it here,

 

[Dexterwarrior12]

Hi everyone
I've started a site which will provide you with solved papers showing all the steps in the working and with useful tips on the side. The best part is that when you look at a solved paper, you can look at commonly made mistakes and learn from them.
Please do check it out!
https://sites.google.com/site/fromatoscom/home

Great step, but I'd advice that you do them with pen, ofcourse these have been done, but the later ones, if you ever add them, try doing them with pen because the contrast is quite low so its pretty difficult to read. Anyways, its really cool!

 

[AnujaK]

Thank you! Yeah I'll try and do that. Problem is that I scratch out a LOT while writing so that would be quite an eyesore. I'll make sure that I adjust the contrast and see if it's readable for the next papers. Thank you so much for the feedback, I appreciate it

Great step, but I'd advice that you do them with pen, ofcourse these have been done, but the later ones, if you ever add them, try doing them with pen because the contrast is quite low so its pretty difficult to read. Anyways, its really cool!

 

[Dexterwarrior12]

Is there some specific stuff I should really know of AS for the A2 paper? I know it can come from anywhere maybe, but can anyone tell me if there are some specific topics I should really revise. I personally think Halogens and Kc are asked quite often.

 

[itallion stallion]

Thank you! Yeah I'll try and do that. Problem is that I scratch out a LOT while writing so that would be quite an eyesore. I'll make sure that I adjust the contrast and see if it's readable for the next papers. Thank you so much for the feedback, I appreciate it

When are u gonna do the same for A2 papers!it would be awesome if u take the same initiative for A2 soon,cuz we have papers next week!As students gonna get a great help from your work!

 

[itallion stallion]

Can someone clear my confusion,when we have to calculate solubility of Ag2CO3 we divide the Ksp by 4'and take the cube root.now if we have to calculate solubility of Al2O3,by which no are,we gonna divide the Ksp with and which root are we gonna take!

 

[itallion stallion]

Can someone plz provide me link to any notes where I can understand how to complete the missing electrons questions in past papers,like showing electron sharing in N20 etc.thanks!