Chemistry: Post your doubts here!

[zenyatales]

hi?
this is a question about dehydration of an alcohol to alkenes.
please help !

MCQ w05 q.no. 24

thanks !

 

[zenyatales]

http://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w05_qp_1.pdf
can some1 please explain question no.34....and

Which physical properties are due to hydrogen bonding between water molecules?
1 Water has a higher boiling point than H2S.
2 Ice floats on water.
3 The H−O−H bond angle in water is approximately 104°.

isn't number 3 suppose 2 be correct bcoz water has 105 angle?! but only 1 & 2 r correct

For the second question. The bond angle is 104 degrees, yes, but it is because of the two lone pairs in the Oxygen which bonds to two Hydrogen atoms, thus giving its non-linear angular shape.
Its not because of Hydrogen bonding.


Btw, the question i posted is from the same past paper

 

[sweetiepie]

Some Helpful Notes For Chemistry Paper 1
viewtopic.php?f=26&t=12407

hope this helps

 

[Silent Hunter]

aslam u alikum

i wanted some useful note and understanding of chapter of equilibrium of AS chemistry. especially the equilibrium calculations

Thank You

 

[yuliana95]

aslam u alikum

i wanted some useful note and understanding of chapter of equilibrium of AS chemistry. especially the equilibrium calculations

Thank You

Try:

http://www.revisionworld.co.uk/node/4890
http://www.s-cool.co.uk/a-level/chemist ... on-summary

 

[XPFMember]

aslam u alikum

i wanted some useful note and understanding of chapter of equilibrium of AS chemistry. especially the equilibrium calculations

Thank You

Waalaikumassalam!

for all chem topics: this is a best site if u wanna cover the syllabus points and all that: www.chemguide.co.uk

 

[Silent Hunter]

^^^its according to A levels whole syllabus?

 

[XPFMember]

Yes! exactly the CIE 9701 Chemistry syllabus!

Do check it out...it goes step by step...covers each and every point...open it...u'll get what i mean!

P.S. I have already included this link in the first post...i thought you knew it gud i still shared it

 

[Silent Hunter]

oh sorry for that.... and thanks

 

[Silent Hunter]

http://www.xtremepapers.com/CIE/Interna ... 4_qp_1.pdf

can anybody explain question number 12 ?

 

[unique840]

http://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_w04_qp_1.pdf

can anybody explain question number 12 ?

at a higher temp the curve should be towards right and smaller than the first curve. this is true only in option B and D. but B is the correct ans because the area under the curve should remain same at both the temp which is nt true for option D

 

[CaptainDanger]

Q1 d ) My answer to it is as followed
Final reading error + initial reading error makes it .10 as the error 0.05 so it is doubled...

While marking scheme and examiner reports say something else??? Explain that?

Here are the paper, marking scheme and examiner report :
9701_s09_qp_31.pdf

9701_s09_ms_31.pdf

9701_s09_er.pdf

 

[Dayyanah]

hey
can anyone help me with the data booklet for chem and formulae booklet for math
thanx in advance

wen r the 2011 oct/nov papers gonna b available?

 

[sweetiepie]

after da 1 week of result in Febraury

 

[student]

Questions !!!

-Explain why solid aluminium chloride vapourises at a relatively low temperature ?
-Describe simple test to show NaCl is ionic ?

-Aluminium Cholide has a simple molecular structure and occurs as a dimer Al2Cl6. There are weak molecular forces between the molecules resulting in a low sublimation point.
-Aqueous solution of NaCl conducts electricity.

 

[Silent Hunter]

hey
can anyone help me with the data booklet for chem and formulae booklet for math
thanx in advance

wen r the 2011 oct/nov papers gonna b available?

result coming around in 23 January 2012.... must be after that

 

[hm12]

chem mcq urgent

please explain mcq number 27

http://www.xtremepapers.com/CIE/Interna ... _qp_12.pdf

 

[abcde]

Q1 d ) My answer to it is as followed
Final reading error + initial reading error makes it .10 as the error 0.05 so it is doubled...

While marking scheme and examiner reports say something else??? Explain that?

Here are the paper, marking scheme and examiner report :
9701_s09_qp_31.pdf

9701_s09_ms_31.pdf

9701_s09_er.pdf

What you wrote is mentioned in the er as the mistake made by the majority of the candidates: "Most candidates simply referred to doubling the individual error, taking no account of positive or negative error". In this one mark question, you are supposed to give a precise reason why the max. error in titration is +/- 0.10 cm^3. This is so because the final burette reading could be +0.05 cm^3 and the initial burette reading could be -0.05 cm^3. Upon subtraction, you will get a max. error of : +0.05 - (-0.05) = +0.10 cm^3.
(For instance, if the accurate initial and final readings are 10.00 cm^3 and 30.00 cm^3, you get an accurate titre of 20.00 cm^3. Now since the error is +/-0.05 cm^3, there's a chance your initial and final readings are 9.95 cm^3 and 30.05 cm^3 instead, giving a titre of 20.10 cm^3! So the max. final error is 0.10 cm^3.)

 

[Silent Hunter]

I have a question: In the definations of standard enthalpy change of formation it says that the reactants and products must be in their standard states.

What are the standard states?

 

[abcde]

^The physical states of the reactants and products under standard conditions: 298 K (25*C) and 1 atmospheric pressure.