Chemistry: Post your doubts here!

[mrnt3250]

My gut is saying answer is B. What's the answer?

Explanation please

 

[mrnt3250]

Yes the answer is B.

I kind of understood it myself, but my problem initially was that I didn't test each equation with this table. I thought I can get a straight answer.
So if we draw a table like this we can figure it out:

 

[syed1995]

I kind of understood it myself, but my problem initially was that I didn't test each equation with this table. I thought I can get a straight answer.
So if we draw a table like this we can figure it out:

yea that's exactly how it will be done.. Btw how did you make such a nice chart? cuz if I had solved it .. it would have been cluttered on the page...

Initial = 2
Final = 2- 2x -- > Q +x

2-2x --> Q + x

2-2x + Q + x = 2+x
2-x + Q = 2+x
Q = 2x

2P --> 2Q + R

 

[mrnt3250]

yea that's exactly how it will be done.. Btw how did you make such a nice chart? cuz if I had solved it .. it would have been cluttered on the page...

Initial = 2
Final = 2- 2x -- > Q +x

2-2x --> Q + x

2-2x + Q + x = 2+x
2-x + Q = 2+x
Q = 2x

2P --> 2Q + R

MS Word + Screenshot + MS Paint + Tinypic.com

 

[PANDA-]

MS Word + Screenshot + MS Paint + Tinypic.com

OR... MS Word + Screenshot + Ctrlv.in

 

[syed1995]

MS Word + Screenshot + MS Paint + Tinypic.com

This right here is the difference between a lazy chump (me) and a hard working student.. Keep up the good work!

 

[mrnt3250]

I've got this doubt always in chemistry.
Could someone post a complete list of types of reactions I must know (for AS Level Chemistry), such as that of acids and bases, carbonates, etc.
Cause sometimes the question wants us to write the products of the reaction, and I'm not sure of the products formed.

 

[PANDA-]

I've got this doubt always in chemistry.
Could someone post a complete list of types of reactions I must know (for AS Level Chemistry), such as that of acids and bases, carbonates, etc.
Cause sometimes the question wants us to write the products of the reaction, and I'm not sure of the products formed.

Well, you can't really memorize every single reaction... That except the organic reactions, which you must memorize, and are laid out very nicely here.. https://www.xtremepapers.com/community/threads/easy-organic-synthesis.24625/
If it's not clear, scroll further.

 

[mrnt3250]

Well, you can't really memorize every single reaction... That except the organic reactions, which you must memorize, and are laid out very nicely here.. https://www.xtremepapers.com/community/threads/easy-organic-synthesis.24625/
If it's not clear, scroll further.

Thanks for that.
But then I don't want to "memorize" all the possible inorganic reactions, more likely I want a list with general product of different reactions. Like for example (I want this type for all of the reaction types), acid + base --> salt + water

 

[syed1995]

Thanks for that.
But then I don't want to "memorize" all the possible inorganic reactions, more likely I want a list with general product of different reactions. Like for example (I want this type for all of the reaction types), acid + base --> salt + water

Well I don't have such a list.. most of it is usually a recall of O levels ....

In Inorganic.. the 3 main reaction for metals are as follows.. which solve most of the problems are..

MgO + H2SO4 --> MgSO4 + H20
Mg + H2SO4 --> MgSO4 + H2
MgCO3 + H2SO4 --> MgSO4 + CO2 + H2O

Al2O3 + 3H2SO4 --> Al2(SO4)3 + 3H2O
Al2O3 + 3NaOH --> Al(OH)3 + Na+
Al(OH)3 + NaOH ---> NaAlO2 + 2H2O

Which can be written as Al2O3 + 2NaOH ---> 2NaAlO2 + H2O ..

Apart from that the periodicity and group II/group VII reactions even I don't remember...

 

[unseen95]

CH3CH2COCl + H2NCH2CH2CH3 = CH3CH2CONHCH2CH2CH3 + HCL , why is the reaction mechanism nucleophilic substitution in this case. Please explain

 

[Alice123]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_23.pdf
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_ms_23.pdf
Q5c(i) ......X is HOCH2CH2CO2H according to the markscheme. If X is heated under reflux with acidified K2Cr2O7, an aldehyde would be produced, so it is supposed to give positive results with 2,4-DNPH..... and can any1 explain what cleavage reactions are?? i havent cum across these before but my teacher said CIE gave cleavage reaction questions in 2011 or 2012, cant remember

 

[iKhaled]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_23.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_23.pdf
Q5c(i) ......X is HOCH2CH2CO2H according to the markscheme. If X is heated under reflux with acidified K2Cr2O7, an aldehyde would be produced, so it is supposed to give positive results with 2,4-DNPH..... and can any1 explain what cleavage reactions are?? i havent cum across these before but my teacher said CIE gave cleavage reaction questions in 2011 or 2012, cant remember

no you are wrong, if X is heated under reflux then complete oxidation will happen and instead of an aldehyde formed you will have a carboxylic acid formed and carboxylic acids do not give positive results with 2,4- dinitrophenylhydrazine. i am sorry but i really don't know what are cleavage reactions and i never heard that name before Oo

 

[PANDA-]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_23.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_23.pdf
Q5c(i) ......X is HOCH2CH2CO2H according to the markscheme. If X is heated under reflux with acidified K2Cr2O7, an aldehyde would be produced, so it is supposed to give positive results with 2,4-DNPH..... and can any1 explain what cleavage reactions are?? i havent cum across these before but my teacher said CIE gave cleavage reaction questions in 2011 or 2012, cant remember

They said before when X is heated with Na2CO3 it gives an effervesence, and what gives effervesence with CO3? Acids.
So now we know it's a -COOH... and it has 3 carbons, so it technically could be propanoic acid, but they said it reacts with K2Cr2O7, which means it has to have an -OH group as well... Now where the -OH goes does matter, we have to know if it's a primary or secondary alcohol, now because they said it reacts to give a product that does not react with 2, 4-DNPH, then it must be primary, because secondary will give ketone, which do react with 2,4-DNPH. So the final formula would be a HOCH2CH2CO2H.

 

[Alice123]

no you are wrong, if X is heated under reflux then complete oxidation will happen and instead of an aldehyde formed you will have a carboxylic acid formed and carboxylic acids do not give positive results with 2,4- dinitrophenylhydrazine. i am sorry but i really don't know what are cleavage reactions and i never heard that name before Oo

I got it now . the aldehyde wasnt distilled off, so a carboxylic acid is produced.....Im forgetting evrything... anyways thanks, im relieved, atleast im not the only one not to knw abt cleavage reactions

 

[Alice123]

They said before when X is heated with Na2CO3 it gives an effervesence, and what gives effervesence with CO3? Acids.
So now we know it's a -COOH... and it has 3 carbons, so it technically could be propanoic acid, but they said it reacts with K2Cr2O7, which means it has to have an -OH group as well... Now where the -OH goes does matter, we have to know if it's a primary or secondary alcohol, now because they said it reacts to give a product that does not react with 2, 4-DNPH, then it must be primary, because secondary will give aldehyde, which do react with 2,4-DNPH. So the final formula would be a HOCH2CH2CO2H.

Primary alcohols give aldehydes on oxidation and secondary ones give ketones AND KETONES AND ALDEHYDES BOTH GIVE POSITIVE RESULTS WIYH 2,4-DNPH

 

[PANDA-]

Primary alcohols give aldehydes on oxidation and secondary ones give ketones

Oh yes, sorry mixed that up, but the primary will not give aldehyde, because the oxidation will take place directly to Carboxylic acid, because it's acidified K2Cr2O7 under reflux, i.e. strong oxidation. But for secondary, there is no further oxidation after ketones.

 

[A star]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_23.pdf
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_ms_23.pdf
Q5c(i) ......X is HOCH2CH2CO2H according to the markscheme. If X is heated under reflux with acidified K2Cr2O7, an aldehyde would be produced, so it is supposed to give positive results with 2,4-DNPH..... and can any1 explain what cleavage reactions are?? i havent cum across these before but my teacher said CIE gave cleavage reaction questions in 2011 or 2012, cant remember

can you specify what is a cleavage reaction?

 

[Alice123]

can you specify what is a cleavage reaction?

Reactions of 1,2-diols give ketones maybe instead of dicarboxylic acids, im not sure

 

[Umar Farooq]

Reactions of 1,2-diols give ketones maybe, im not sure

no they give first Aldehydes then aicds cz the di ols are not the secondry alcohols but primary alcohols...