Chemistry: Post your doubts here!

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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
shorturl.at/iEGT7
2) AS - Atomic structure (including ionisation energy, atomic and ionic radii)
shorturl.at/blzX7
3) AS -Chemical structure and bonding (including intermolecular forces)
shorturl.at/cdfls
4) AS - States of matter (including the gas laws)
shorturl.at/eoxzM
5) AS - Chemical energetics (thermodynamics - enthalpy changes)
shorturl.at/mqDL9
6) AS - Redox changes (oxidation numbers)
shorturl.at/jFHNW
7) AS - Reaction kinetics (qualitative Maxwell-Boltzmann distribution)
shorturl.at/lwCW8
8) AS - Chemical equilibria (Le Chatelier, equilibrium constants)
shorturl.at/ntvP6
9) AS - 9.1 - General periodicity
shorturl.at/pIKT6
10) AS - 9.2 - Group 2 chemistry (qualitative trends, reactions)
shorturl.at/uDGZ7
11) AS - 9.3 - Group 17 chemistry
shorturl.at/pAWY8
12) AS - 9.4 - Nitrogen and sulfur chemistry
shorturl.at/nvJMP
13) AS - 10.1 - Introductory organic chemistry (isomerism, naming, reaction types)
shorturl.at/tzBI6
14) AS - 10.2 - Hydrocarbons (alkanes and alkenes)
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15) AS - 10.3 - Addition polymerisation
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16) AS - 10.4 - Alcohols
shorturl.at/hmABZ
17) AS - 10.5 - Halogenoalkanes
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18) AS - 10.6 - Carbonyl compounds (aldehydes and ketones)
shorturl.at/pqBEO
19) AS - 10.7 - Carboxylic acids and its derivatives
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20) AS - 10.8 - Simple organic nitrogen compounds (amines)
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21) AS - infra-red spectroscopy
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22) A2 - energetics (entropy, Gibbs, feasibility)
shorturl.at/mtS19
23) A2 - reactions kinetics (orders, rate determining step, etc)
shorturl.at/hkCX0
24) A2 - transition metals
shorturl.at/lwHW4
25) A2 - redox chemistry (advanced electrochemistry, cell potential, etc)
shorturl.at/exzAV
26) A2 - Group 2 (thermal stability and solubility essays)
shorturl.at/juyzV
27) A2 - ionic equilibrium (acids, bases, Kw, Kpc, Ksp)
shorturl.at/kpD04
28) A2 - aromatic chemistry (benzene and its derivatives)
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29) A2 - halogenoarenes
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30) A2 - phenols
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31) A2 - phenylamines and amides
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32) A2 - Comparing relative acidities and basicities of organic compounds
shorturl.at/mxD18
33) A2 - amino acids and proteins (including electrophoresis)
shorturl.at/tvBWY
34) A2 - polymerisation
shorturl.at/cCDW8
35) A2 - analytical chemistry (NMR, mass spec, chromatography)
shorturl.at/ovw12
 
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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
 
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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.

 
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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?
 
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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?
 

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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? :pardon:
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.
 
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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? :pardon:

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.
 
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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
 
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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?
 
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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.
 
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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
 
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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 25.0 cm of 0.100 mol dm sodium hydroxide solution.
what could be the identity of X?
Al2O3
MgO
P4O10
SO3
 
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Hi guys, so about half a year ago, when I was writing up my thesis, I was inspired to start my own Chemistry tutorial channel. It has since humbly continued to attract more viewers (students/learners, I assume) globally.

www.youtube.com/c/ptetchemistry

I have recently resumed teaching, albeit at a different level, and I have continued to update my channel (in my own free time) with more teaching and learning resources including lectorials (lecture tutorials), practical videos, alternative to practical (for those who did not get the chance to actually work in the laboratory) and importantly, my think-aloud tutorials for exam questions.

It is not a fancy channel, but an educational one at best. In my previous work, I was (and still am!) an accomplished synthetic organometallic chemist, working with some of the most air-sensitive compounds. My passion is however in advancing chemical education and affording equal opportunities for all who want to learn from me.

The topical playlists for O/IGCSE/GCSE (pure chemistry and combined science chemistry) make it suitable for any 14-16 years old at various stages of the curriculum, while that for A/IB make it suitable for any 16-18 years old too.

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