Chemistry: Post your doubts here!

[knowitall10]

but will that affect the total mark of the paper? like for example if a question has been canceled because the majority of the candidates didn't do it and its worth 5 marks the total mark of the paper will be 95 for example instead of 100 ?

I don't think they'll cancel the paper... they might just be lenient. beacuse its not just us giving this exam: Pakistan, India, Dubai (Mostly Paks and Ind's), Saudi Arabia... and out of all of them, its just the Saudi candidates (regardless of the nationality) who are the dumbest (lol jk). Pak's and Ind's have their IQ levels peaking higher than mount everest... what i'm sure of is that the grade threshold would be lowered. plus, p5 doesnt really play an important role in our overall grades.. its our AS and P4 that carry the greatest weight.

 

[iKhaled]

Just give me a few minuted to attempt the graph then i'll check and compare the ER

show ur graph when u r done pls!!

 

[knowitall10]

show ur graph when u r done pls!!

Yesss!! Please!

 

[knowitall10]

I'm pretty sure thats the only way to make allowances. Either that or giving the marks to all candidates. But thats not something to stress about. Point is, be vigilant and read everything closely and make intelligent informed decisions on the paper!
IA We wont have to face anything so weird!

Hey, MaxStudentALevel, i'm not studying in Pakistan.."intelligent informed decisions" doesnt apply here

 

[MaxStudentALevel]

Hey, MaxStudentALevel, i'm not studying in Pakistan.."intelligent informed decisions" doesnt apply here

LOLLLL HAHAHHAA I'm not from here either, moved here at the beggining of O levels

 

[MaxStudentALevel]

show ur graph when u r done pls!!

Sure!

 

[goodluckayesha]

There's no hydrogen bond between CH3F molecules because there is no H-F bond, F is bonded to C here, not H. Also, in aldehydes, there's no H-O bond, the O is bonded to C. I suggest you revise hydrogen bonding from the textbook.

Hydrogen bonding occurs between H that is bonded to F, O or N in one molecule, and F, O or N bonded to H in another molecule..
Examples:
NH3 can form hydrogen bonds with water.
N-H ---- O-H

HF can form hydrogen bonds with water as well.
H-F ---- O-H

H from one CH3F molecule cann bond to F from another CH3F molecule? no?

 

[xhizors]

Assalamu alaykum.
Can someone please explain the mark scheme of M/J 11 Paper 53 Q1 c?
I don't understand how we use the water bath with the reagents provided and i do not know what the thermometer range must be.
Jazakum Allahu Khair.

You place The Container with Solution in a bath with a constant concentration of both the reagents and measure the time for flask becoming opaque or any cross getting disappear at a setted Temperature then u vary the temperature for next experiments !!
For temparature
Always remember to state on thermometer a minimum and a maximium point 0`C and 100`C with a graduations of either 0.1`C or 0.2 `C
In a Enthalphy Change of Combustion use 0.1`C graduations

btw column headings for winter 10 53 Q2
aren't on ms

hope it helps

 

[MaxStudentALevel]

H from one CH3F molecule cann bond to F from another CH3F molecule? no?

For hydrogen bonding, there would have to be a covalent bond between the H and F. In CH3F, the covalent bonds are C-H and C-F, so no hydrogen bonding.

It is dipole-dipole, as the F is very electronegative, and H is less electronegative than C, forming a negatively charged 'end' which can interact with neighbouring molecules.

 

[goodluckayesha]

For hydrogen bonding, there would have to be a covalent bond between the H and F. In CH3F, the covalent bonds are C-H and C-F, so no hydrogen bonding.

It is dipole-dipole, as the F is very electronegative, and H is less electronegative than C, forming a negatively charged 'end' which can interact with neighbouring molecules.

hmm yaa got it thnq

 

[iKhaled]

H from one CH3F molecule cann bond to F from another CH3F molecule? no?

yes it can but not hydrogen bonds. this will be permanently dipole-dipole bonds

 

[knowitall10]

You place The Container with Solution in a bath with a constant concentration of both the reagents and measure the time for flask becoming opaque or any cross getting disappear at a setted Temperature then u vary the temperature for next experiments !!
For temparature
Always remember to state on thermometer a minimum and a maximium point 0`C and 100`C with a graduations of either 0.1`C or 0.2 `C
In a Enthalphy Change of Combustion use 0.1`C graduations

btw column headings for winter 10 53 Q2
aren't on ms

hope it helps

Thanks a lot Jazak Allah!
But how do we heat the mixture?
the bunsen burner will burn the paper underneath my conical flask...

 

[xhizors]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_53.pdf
question 2 please the first part

Use c1v1= c2v2 for each column
so first Row workout With 0.1 NaOH is (0.1x24.3)/10
Note: we didn't conver cm3 to dm3 as both volumes are in cm3 else we would have to divide each volume by 1000

 

[MaxStudentALevel]

Use c1v1= c2v2 for each column
so first Row workout With 0.1 NaOH is (0.1x24.3)/10
Note: we didn't conver cm3 to dm3 as both volumes are in cm3 else we would have to divide each volume by 1000

AHHH THAT MAKES SO MUCH SENSE THANKS!

 

[xhizors]

Thanks a lot Jazak Allah!
But how do we heat the mixture?
the bunsen burner will burn the paper underneath my conical flask...

Water Bath is Thermostatically Controlled Apparatus this is more handy when u have to vary temperatures then a bunsen burner!
so y u want to place a paper above bunsen burner beneath conical flask ?

 

[knowitall10]

Use c1v1= c2v2 for each column
so first Row workout With 0.1 NaOH is (0.1x24.3)/10
Note: we didn't conver cm3 to dm3 as both volumes are in cm3 else we would have to divide each volume by 1000

yeah, that ddnt occur to me.. C1V1=C2V2 makes sense.. nice...

 

[knowitall10]

Water Bath is Thermostatically Controlled Apparatus this is more handy when u have to vary temperatures then a bunsen burner!
so y u want to place a paper above bunsen burner beneath conical flask ?

ahh.. thats what i ddnt get... but now i do, thanks a lot
Jazak Allahu Khair!

 

[xhizors]

w

OH NO!!! I think it does matter! Read the examiner's report on this question. column D's heading must be 0.1B/20 based on the 2:1 mole ratio principle!
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_er.pdf

hat is the second column reading

 

[applepie1996]

Use c1v1= c2v2 for each column
so first Row workout With 0.1 NaOH is (0.1x24.3)/10
Note: we didn't conver cm3 to dm3 as both volumes are in cm3 else we would have to divide each volume by 1000

i have a question though after we get the concentration won't we have to divide it by 2 ?

 

[MaxStudentALevel]

i have a question though after we get the concentration won't we have to divide it by 2 ?

Yes! But you put that in the expression! So instead of B*0.1/10 it becomes B*.1/20 !!