Chemistry: Post your doubts here!

[snowbrood]

heyy easy there -_- u r talking to a GIRL who cant stand BIO even having been studying it for 5 years straight :/
yh well i get it where u're standing actually ..... but i haven't done applications yet so i'm afraid i cant help u all that much. my only advice would be to consult more sources on this particular topic. see if there are any relevant lectures on Khanacademy.com and search the webb life like said before. maybe you'll get a hang of it. and i am guessing that if this is a very basic chap then it must be o levels biology stuff so just imagine that u r studying it for the first time in o levels and have to learn it or something? Good Luck... maybe in a few months wen i have done it then i can be of more help. if later on you need help with any specific concepts of this stuff then tell me /... i'll try my best to help u out =)

believe me its not a basic stuff lol

 

[daredevil]

believe me its not a basic stuff lol

hahaha okay

 

[crys123]

ok ok sorry! i studied bio and believe me compared to what i had to study in bio, this is actually the easy one. And i said it so that you dont get scared of the chapter. coz it happened to me, somebody told me that moles is extremely hard and i ended up struggling the most with moles, for 2 years in school! I get it now and its not hard. i'll help if i can. post your questions. hope this helps a bit.

 

[crys123]

why is the ans Be and not Mg?

 

[crys123]

the ans is C. plz explain someone!

 

[strangerss]

HEY every one ,alsalum allaykom . I have a query , what is the use of the chemistry application support booklet for a2 students? am I supposed to study all the information ? hope some one can clear my doubt

 

[Kim Shaw]

hey guys, please help me with this question in equilibria. answer is C. Please explain why..
View attachment 33489

Hi...plz help me with this question! Its been a week now n no one seems to be answering it

 

[Kim Shaw]

iron tablets can be bought at chemists to supplement the diet. they contain iron(II)sulfate. which one of the following aqueous reagents could be used under suitable conditions to determine the percentage of iron in the tablets by titration?
A.ethanedioic acid B.Iodine in potassium iodide C.potassium manganate(VII) D.sodium thiosulfate
ans C..plz tell me why C and not the others..thnx

Also this one..plz plz plz!!

 

[ShreeyaBeatz]

Hey !
Please help me with this question.


The reaction between Fe3+ ions and I–
ions is an equilibrium reaction.
2Fe3+(aq) + 2I– (aq) gives 2Fe2+(aq) + I2(aq)


The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.
[Fe3+(aq)] = 2.0 × 10–4 mol dm–3
[I2(aq)] = 1.0 × 10–2 mol dm–3

Use these data, together with the equation to calculate the concentrations
of Fe2+(aq) and I–
(aq) at equilibrium

 

[Kim Shaw]

Hey !
Please help me with this question.


The reaction between Fe3+ ions and I–
ions is an equilibrium reaction.
2Fe3+(aq) + 2I– (aq) gives 2Fe2+(aq) + I2(aq)


The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.
[Fe3+(aq)] = 2.0 × 10–4 mol dm–3
[I2(aq)] = 1.0 × 10–2 mol dm–3

Use these data, together with the equation to calculate the concentrations
of Fe2+(aq) and I–
(aq) at equilibrium

According to the equation,
2moles Fe3+ react with 2 moles I-
so at equilibrium, [Fe3+]=[I-]
hence [I-]= 2.0 × 10–4 mol dm–3

Also, according to equation,
2moles Fe2+ react with 1 mole I2
so at equilibrium [Fe2+]=2[I2]
[Fe2+]=2×1.0 × 10–2 mol dm–3
=2.0 × 10–2 mol dm–3
Hope it helped

 

[Snowysangel]

why is the ans Be and not Mg?

Yeah I don't get this either.. I think it's to do with their ionization energies but i can't be sure. Could someone please answer this

 

[strangerss]

hey please can some one reply to my question about whether a2 students should memorize the chemistry application support booklet?

 

[Yash Jain]

freiends, can you please help me with following questions:-
9701_s07_qp1=> Q no. 9 and 13
9701_s08_qp1=> Q no. 5
9701_w08_qp1=> Q no. 3, 5 and 10
9701_s09_qp1=> Q no. 12
9701_w09_qp1=> Q no. 1 and 9

 

[asma tareen]

hey please can some one reply to my question about whether a2 students should memorize the chemistry application support booklet?

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

 

[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???