Chemistry: Post your doubts here!

[daredevil]

Arent we provided with it in exams :/???

no! it's the DATA BOOKLET we are provided with NOT the applications booklet. Applications booklet is issued by CIE and serves as a textbook for a part of paper 4. It is basically an extension of the Core Syllabus in a way.

 

[Kim Shaw]

why is the ans Be and not Mg?

In the periodic table, there are diagonal relationships. This is when elements which are diagonal to each other possess similar properties. if u look in the periodic table, u will see that Be is diagonal to Al, the same way as Li is diagonal to Mg and B is diagonal to Si.

There are several reasons for this, but each depends on the way atomic properties like electronegativity vary around the Periodic Table.
As an explanation to the diagonal relationship with regard to electronegativity read this:

Electronegativity increases across the Periodic Table. So, for example, the electronegativities of beryllium and boron are:

Be1.5
B2.0

Electronegativity falls as you go down the Periodic Table. So, for example, the electronegativities of boron and aluminium are:

B2.0
Al1.5

So, comparing Be and Al, you find the values are (by chance) exactly the same.

The increase from Group 2 to Group 3 is offset by the fall as you go down Group 3 from boron to aluminium.

Something similar happens from lithium (1.0) to magnesium (1.2), and from boron (2.0) to silicon (1.8).

In these cases, the electronegativities aren't exactly the same, but are very close.

Similar electronegativities between the members of these diagonal pairs means that they are likely to form similar types of bonds, and that will affect their chemistry.
Thus, answer is Be rather than Mg

 

[Kim Shaw]

the ans is C. plz explain someone!

• Fluoride and chloride ions won't reduce concentrated sulphuric acid, as they are not strong enough reducing agents.
  
  
• Bromide ions reduce the sulphuric acid to sulphur dioxide. In the process, the bromide ions are oxidised to bromine.
  
  
• Iodide ions reduce the sulphuric acid to a mixture of products including hydrogen sulphide. The iodide ions are oxidised to iodine.
  
  
• Reducing ability of the halide ions increases as you go down the Group 7.

As a kind of explanation of why this is the case read this:
When a halide ion acts as a reducing agent, it gives electrons to something else. That means that the halide ion itself has to lose electrons.

The bigger the halide ion, the further the outer electrons are from the nucleus, and the more they are screened from it by inner electrons. It therefore gets easier for the halide ions to lose electrons as you go down the Group because there is less attraction between the outer electrons and the nucleus.

Thus, answer can only be C

 

[asma tareen]

no! it's the DATA BOOKLET we are provided with NOT the applications booklet. Applications booklet is issued by CIE and serves as a textbook for a part of paper 4. It is basically an extension of the Core Syllabus in a way.

Hmmm k thanks

 

[strangerss]

no! it's the DATA BOOKLET we are provided with NOT the applications booklet. Applications booklet is issued by CIE and serves as a textbook for a part of paper 4. It is basically an extension of the Core Syllabus in a way.

So I'm supposed to memorize all the information in it???

 

[strangerss]

no! it's the DATA BOOKLET we are provided with NOT the applications booklet. Applications booklet is issued by CIE and serves as a textbook for a part of paper 4. It is basically an extension of the Core Syllabus in a way.

So I'm supposed to memorize all the information in it???

 

[daredevil]

So I'm supposed to memorize all the information in it???

ummm I haven't actually started the application booklet yet in school but as far as i think... yeah i think you have to prepare it like you would prepare any other part of the syllabus. understand it, practice it and learn it.

 

[strangerss]

ummm I haven't actually started the application booklet yet in school but as far as i think... yeah i think you have to prepare it like you would prepare any other part of the syllabus. understand it, practice it and learn it.

I just rechecked the syllabus content and yes like you said all the chemistry of life topics are included! (more pressure XS) thanks for answering , btw do you have any idea where I can find p5 notes or classified past papers?

 

[daredevil]

I just rechecked the syllabus content and yes like you said all the chemistry of life topics are included! (more pressure XS) thanks for answering , btw do you have any idea where I can find p5 notes or classified past papers?

umm the past papers are available on xtremepapers' papers section.
the notes ... well there are no hard and fast set notes but check out the apparatus you are allowed to use in p5 as well as the volumes because mentioning the volumes in the p5 experiments is REALLY IMPORTANT. other than that search the xpc forum for paper 5 notes. I'm sure you'll get some help. I'll upload the ones I found too .... I found these on some forum or the other on xpc...
And yeah the most important thing is to practice past papers of paper 5 along with the marking schemes and examiner reports (all are available on papers.xtremepaper.com). My advice will be to start from 2013 and move backwards from there yearly doing your own variants first and then move on to the other variants. That will give you more than enough practice for paper 5

Best of Lcuk

 

[strangerss]

umm the past papers are available on xtremepapers' papers section.
the notes ... well there are no hard and fast set notes but check out the apparatus you are allowed to use in p5 as well as the volumes because mentioning the volumes in the p5 experiments is REALLY IMPORTANT. other than that search the xpc forum for paper 5 notes. I'm sure you'll get some help. I'll upload the ones I found too .... I found these on some forum or the other on xpc...
And yeah the most important thing is to practice past papers of paper 5 along with the marking schemes and examiner reports (all are available on papers.xtremepaper.com). My advice will be to start from 2013 and move backwards from there yearly doing your own variants first and then move on to the other variants. That will give you more than enough practice for paper 5

Best of Lcuk

Thank you so much for the help and advice , I could use all the help needed because right now .So do you think I should start solving p5 even if I still haven't finished the syllabus?

 

[daredevil]

Thank you so much for the help and advice , I could use all the help needed because right now .So do you think I should start solving p5 even if I still haven't finished the syllabus?

Yes you should. do you remember the atp paper from o levels? paper 5 is more or less the same in essence as the atp paper. except that in this paper we need to DESIGN and ANALYZE the experiment procedure and not just work on the results. So it can be done (mostly) without the syllabus help as well.
I could give you the links for the papers and questions that we have done in class up till now if you want... we haven't completely done the syllabus but we did do these papers... they are just 8 questions btw.. so maybe it would be better if you see for yourself the papers and which questions you can do and stuff.... Best of Luck.
and no problem

 

[ahmed abdulla]

how to find C and D ...?
i got C as blue and D as red ... but in marking scheme its the opposite ! ..
is it the mistake of marking scheme ?

 

[Arjun12345]

need chemistry worksheets a level classified topic by topic plzzzz plzzzzzz

 

[strangerss]

Yes sure if y

Yes you should. do you remember the atp paper from o levels? paper 5 is more or less the same in essence as the atp paper. except that in this paper we need to DESIGN and ANALYZE the experiment procedure and not just work on the results. So it can be done (mostly) without the syllabus help as well.
I could give you the links for the papers and questions that we have done in class up till now if you want... we haven't completely done the syllabus but we did do these papers... they are just 8 questions btw.. so maybe it would be better if you see for yourself the papers and which questions you can do and stuff.... Best of Luck.
and no problem

Yes sure if you don't mind thanks a lot

 

[strangerss]

how to find C and D ...?
i got C as blue and D as red ... but in marking scheme its the opposite ! ..
is it the mistake of marking scheme ?

As far as I understand you're supposed to take the color opposite to that of the color absorbed , because the color absorbed is not the one that will be reflected into our eyes , that means anything other than the color blue absorbed is the one our eye will see get it? do you have an idea about the simple color wheel? in the question if blue was absorbed the color red is the one that our eyes will see because it is opposite to the color blue in the color wheel. Here take a look at this pic. I know orange is the opposite in the pic. but the option wasn't provided so red is the closest so blue is opposite to red and red is opposite to blue ..hope I made any sense hehe

 

[yousef]

For converting Methyl benzene To Chloromethyl benzene .. in the Free radical substitution ...we need
Cl2 and hf as reagent and condition .. as stated in marking scheme ..
My question is what is ( hf ) ?

 

[daredevil]

For converting Methyl benzene To Chloromethyl benzene .. in the Free radical substitution ...we need
Cl2 and hf as reagent and condition .. as stated in marking scheme ..
My question is what is ( hf ) ?

hydrogen floride

 

[yousef]

hydrogen floride

is it that simple
But does it make sense adding hf to methyl beneze .. i mean there should be a flouride in the compound ?
we know that hydrogen fluoride is HF most probably it stands for a condition

 

[daredevil]

is it that simple
But does it make sense adding hf to methyl beneze .. i mean there should be a flouride in the compound ?
we know that hydrogen fluoride is HF most probably it stands for a condition

yeah well it does seem kinda weird ...
actually the way I have it in my notes, you need Cl2 as a reactant and ultraviolet rays (UV rays) as the catalyst typ ething you know the one you mention above the arrow...
I havent even ONCE used HF instead but thats what HF is i think.... google it?

 

[daredevil]

Yes sure if y

Yes sure if you don't mind thanks a lot

here you go
Pleanning: N10/p51/Q1
J10/p51/Q1
N09/p52/Q1
J09/Q1

Analysis and Evaluation: J10/p51/Q3
N09/52/Q3
N08/Q2
J07/Q2