Chemistry: Post your doubts here!

[ptet.chemistry]

Help please!!!

Well you should always have tried something, i.e. outline your ideas then people can just help to guide you along. Remember, if you don't do that and just rely on someone explaining from zero, you risk losing it all big time in the real exam. By then it becomes too late.

Go for option 2 => since these involve specific isotopes, they both have mass of 34. Even if you remove some of the dioxygen, the average mass will remain the same.

Check number 1. Same deal with option 2. Average mass will just be 34 because all the molecules present have mass of 34.

Check number 3. H2S + 3/2 O2 --> SO2 + H2O (to balance the eqn - gcse/o level, no). I leave you to think about limiting and excess reactant based on the reacting mole ratio, and the information that you have equal number of these two molecules in the mixture. It all comes down is 3 correct or not.

 

[Hamnah Zahoor]

Help please!!!

Sorry I couldn't reply in time and i guess ptet.chemistry explained it well enough but still if you don't understand it you can ask.

 

[s_t_u_d_e_n_t]

Does anyone have topical CIE A level chemistry past papers?

 

[Mr.Physics]

Does anyone have topical CIE A level chemistry past papers?

I believe this site has all the resources you'll need:

CIE A-level Chemistry (9701) Revision - PMT

Revision for CAIE AS and A-level Chemistry (9701) papers, including summary notes, videos, worksheets and past exam questions by topic.

www.physicsandmathstutor.com

 

[ptet.chemistry]

Check out my topical chemistry A Level tutorials. Subscribe to the channel for updates and share widely with group chat and friends please, if you find them useful. Good luck.


Why settle for less when an A*/A is up for grabs?
What: topical playlist for A Level/IB/Pre-U chemistry
Who: AS/A/IB Level students (16-18 pre-university, junior college level)
Why: My subject expertise, my teaching experience, my commitment to excellence, your desire to learn
To do: Subscribe and share widely if you find these useful.
Main channel (navigate the playlist): www.youtube.com/c/ptetchemistry

Shortened YouTube playlist links
1) AS - Mole concept and stoichiometry calculations
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2) AS - Atomic structure (including ionisation energy, atomic and ionic radii)
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5) AS - Chemical energetics (thermodynamics - enthalpy changes)
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7) AS - Reaction kinetics (qualitative Maxwell-Boltzmann distribution)
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9) AS - 9.1 - General periodicity
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10) AS - 9.2 - Group 2 chemistry (qualitative trends, reactions)
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11) AS - 9.3 - Group 17 chemistry
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14) AS - 10.2 - Hydrocarbons (alkanes and alkenes)
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19) AS - 10.7 - Carboxylic acids and its derivatives
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22) A2 - energetics (entropy, Gibbs, feasibility)
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27) A2 - ionic equilibrium (acids, bases, Kw, Kpc, Ksp)
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32) A2 - Comparing relative acidities and basicities of organic compounds
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33) A2 - amino acids and proteins (including electrophoresis)
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34) A2 - polymerisation
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35) A2 - analytical chemistry (NMR, mass spec, chromatography)
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[Madina2410]

Help pls

 

[Filth1212]

View attachment 65374Help please

This is a biology question, the answer is disulfide as it is covalent and breaks last.

 

[Filth1212]

View attachment 65625Help pls

Since $$H_2SO_4$$ is a strong acid it will dissociate fully into $$H^+$$ ions, $$HSO_4^-$$ is the conjugate base and further dissociates into $$SO_4^{2-}$$ ions and protons therefore the solution wont contain an equal number of $$H^+$$ and $$HSO_4^-$$ ions so 2 is incorrect, hence since 2 is incorrect the only option available is D.

Also wait r u from sir shoukats class because i swear i just answered this question there rn

 

[ptet.chemistry]

Anyone doing CIE Chemistry variant 13?

Check out my full Paper 1 tutorials, and enjoy my take on thinking out loud through the different papers. It is more important to be able to work things out than simply doing without understanding why and the how.

Check the other topical MCQ playlists too as well as other A level chemistry related playlists ranging across all the different topics, components.

Subscribe and share with friends, class group chats, juniors/seniors from school, anyone else you think the channel might be useful for. Cheers.

A Level Chemistry Paper 1 MCQ tutorials - also check topical MCQs

Hi all, other topical MCQ playlists for A Level chemistry are very useful for covering theory contents and to see variations of questions/concepts tested. Ch...

www.youtube.com

 

[Claire MK]

View attachment 54323
For optical isomerism, you need a carbon with a chiral center ( 4 different substituents on the C)
As you can see only 1,2 and 3 have a chrial carbon (marked red)
So it is B

thank youuuuu

 

[kent123]

chemistry past paper mayjune 2011 paper 22. (s11_22).
number 1. 1ci.
I still couldn't process why it is directly 0.04. I thought 0.04 reacted so why didn't it subtract 1-0.04 = 0.06 for ethanoic acid?

 

[kent123]

i have attached two files here: a question paper and its markscheme. Please do help me with number 6b as soon as possible. Why 19.10 (which I think is got directly from the titre of titration 5). Why not sum up all titre values then divide by 5, I had got 19.23? How am I calculating wrong, or where am I not understanding the question?

 

[kent123]

Can any one help me in getting chemistry an physics notes? plz its urgent! God bless you guys. thnx :friends:

You can view as and a level chemistry notes here https://mathsmadeeasy.co.uk/a-level-chemistry-revision/
Physics https://mathsmadeeasy.co.uk/a-level-physics-revision/

 

[kent123]

http://www.xtremepapers.com/CIE/Interna ... _qp_11.pdf

number 4. Why is the answer C and not D? With a catalyst, activation energy is lowered isnt it? ardon:

in diagram 1, the higher temperature must be Q due to more molecules with high energy/ energy greater than ea, and less molecules with low energy.
in diagram 2, yes catalyst lowers the Ea, so only a small value of molecular speed is required for particles to make successful collisions. Less Ea, less speed necessary for particles. So it's X.
Thus C.

 

[kent123]

http://www.xtremepapers.com/CIE/Interna ... _qp_11.pdf

number 4. Why is the answer C and not D? With a catalyst, activation energy is lowered isnt it? ardon:

in diagram 1, the higher temperature must be Q due to more molecules with high energy/ energy greater than ea, and less molecules with low energy.
in diagram 2, yes catalyst lowers the Ea, so only a small value of molecular speed is required for particles to make successful collisions. Less Ea, less speed necessary for particles. So it's X.
Thus C.

 

[ptet.chemistry]

i have attached two files here: a question paper and its markscheme. Please do help me with number 6b as soon as possible. Why 19.10 (which I think is got directly from the titre of titration 5). Why not sum up all titre values then divide by 5, I had got 19.23? How am I calculating wrong, or where am I not understanding the question?

If you had done any A Level titrations, you should be aware of what concordant titres within +/-0.10 cm3 is the maximum acceptable. You are going to be marked within that margin relative to that of your teacher/centre supervisor who has to do the titration using the same batch of chemicals you did, and that is how titration accuracy marks are marked. Looking at the five readings, you should be able to see that reading 1 is comparatively different from the others. I didn't check all the titres, I just quickly glanced over them, so you get to them again.

Check out my chemistry tutorial channel for more useful insights on how to think through theory level questions, as well as experimental planning, analysis and evaluation...a skill many students often lack but are assessed in practical components as well.

Subscribe and share the channel with friends, chat groups, juniors/seniors from school, etc. Cheers.

www.youtube.com/c/ptetchemistry

 

[Bobo17]

NOVEMBER 2015 P11 QUESTION 16

X is the oxide of a Period 3 element. X reacts with water to give an acidic solution.
A solution is prepared by reacting 0.100g of X with excess water. This solution was neutralised
by exactly 25.0cm3 of 0.100 moldm–3 sodium hydroxide solution.

What could be the identity of X?
A A l2O3
B MgO
C P 4O10
D SO3


Can anyone explain why answer is D?

 

[kent123]

hi. so3 + 2naoh ->na2so4 + h2o
mol of NaOH = 2.5 x 10^-3 mol = 2 x mol of SO2
mol of SO2 = 1.25 x 10-3 mol
Mr of X oxide = mass / mol = 0.1 / 1.25x10^-3 = 80 g/mol

SO3 is (3 x 16) + 32 = 80 g/mol

i did this backwards, knowing the answer as you've told. u can do it forwards by writing down each balanced equations and see which one fits.

 

[Jawahir Ghafoor]

here, can somebody explain me question 16 part (c) ??
the markscheme answer is pentane.

 

[Hamnah Zahoor]

here, can somebody explain me question 16 part (c) ??
the markscheme answer is pentane.

i wasn't able to find even a clue
I guess the question was wrong because as according to the above equation none of the options are correct. Is this a whole question from a paper? if yes please mention the year and variant.
if this is your school exam they might have mixed the question options