Chemistry: Post your doubts here!

[robinhoodmustafa]

What?

Ionic compound are basic and Covalent ones are acidic. so how come to wrote 'thus an acid'

 

[AbbbbY]

Ionic compound are basic and Covalent ones are acidic. so how come to wrote 'thus an acid'

Firstly that is a very, very crude and rudimentary method to define acids and bases.

Secondly, ionic BEHAVIOR isn't the same as ionic-compound. Lets say someone is a man and behaves like a woman. He wont be a woman. Just a man who behaves like one. Get it?

Likewise, due to the H-Cl polarity, the bond with H2O present can from hydronium ion and chloride ion. (H3O+ and Cl-) (can also write it as H+ and Cl- but that wouldn't make sense further on). H3O+ is a proton donor, and thus classified as an acid.

 

[AbbbbY]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
can someone PLEASEEEE explain question 5b(iv)?!

Oh this question has given me a lot of trouble lately.

I went with (21/1)*(1/9) = 21/9 = 7/3


My explanation was something like 21/1 = ratio of rate of tertiary to primary H. 1/9 = ratio of tertiary to primary H present. Ratio of J/K = 21/1 * 1/9 = 21/9 = 7/3

J= Tertiary Hydrogen replaced.
K= Primary Hydrogen replaced.

 

[Logitech]

Guys I have a doubt. Now if we have an alkene, for example but-2-ene, when we react it with K2Cr2O7 it'll form CH3CH(OH)CH(OH)CH3 right? But what if we have an alkene with double bond at 2 different places like hex-2,5-ene, if we react this with K2Cr2O7 will a diol occur in both places?
Another question is when they ask for a reagent and the answer is potassium dichromate, should I write K2Cr2O7 or Cr2O7 2- or Cr2O7/H+ ?

 

[robinhoodmustafa]

Guys I have a doubt. Now if we have an alkene, for example but-2-ene, when we react it with K2Cr2O7 it'll form CH3CH(OH)CH(OH)CH3 right? But what if we have an alkene with double bond at 2 different places like hex-2,5-ene, if we react this with K2Cr2O7 will a diol occur in both places?
Another question is when they ask for a reagent and the answer is potassium dichromate, should I write K2Cr2O7 or Cr2O7 2- or Cr2O7/H+ ?

Yes. Both double bond with be broken and replace by OH on 5th and 2nd carbon bond. try drawing displayed formula.it really helps
and Cr2O7/H+ is liked by examiner. Mostly this is written in MS but K2Cr2O7 wont loose u marks.

 

[itallion stallion]

Can someone plz help me with this
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
Q5biv
Thanks!

 

[AbbbbY]

Yes. Both double bond with be broken and replace by OH on 5th and 2nd carbon bond. try drawing displayed formula.it really helps
and Cr2O7/H+ is liked by examiner. Mostly this is written in MS but K2Cr2O7 wont loose u marks.

It will if you don't write ACIDIFIED.

Acidified K2Cr2O7 or (Cr2O7)2-/H+

 

[AbbbbY]

Can someone plz help me with this
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_43.pdf
Q5biv
Thanks!

Oh this question has given me a lot of trouble lately.

I went with (21/1)*(1/9) = 21/9 = 7/3


My explanation was something like 21/1 = ratio of rate of tertiary to primary H. 1/9 = ratio of tertiary to primary H present. Ratio of J/K = 21/1 * 1/9 = 21/9 = 7/3

J= Tertiary Hydrogen replaced.
K= Primary Hydrogen replaced.

 

[Suchal Riaz]

It will if you don't write ACIDIFIED.

Acidified K2Cr2O7 or (Cr2O7)2-/H+

if u don't write acidified or H+ or H2SO4 then u will not get marks.

 

[AbbbbY]

if u don't write acidified or H+ or H2SO4 then u will not get marks.

....which is exactly what I stated up there.

 

[Namehere]

Guys I have a doubt. Now if we have an alkene, for example but-2-ene, when we react it with K2Cr2O7 it'll form CH3CH(OH)CH(OH)CH3 right? But what if we have an alkene with double bond at 2 different places like hex-2,5-ene, if we react this with K2Cr2O7 will a diol occur in both places?
Another question is when they ask for a reagent and the answer is potassium dichromate, should I write K2Cr2O7 or Cr2O7 2- or Cr2O7/H+ ?

Isn´t this supposed to be with cold dilute acidifed KMnO4?

 

[itallion stallion]

From where have u brought this 9?

 

[AbbbbY]

Isn´t this supposed to be with cold dilute acidifed KMnO4?

Exactly what I was thinking. Was trying to jog my memory and see where in alkene reactions K2Cr2O7 was used. All I can remember is Cold dil KMnO4 -> Di-ol, hot conc -> cleavage.

 

[robinhoodmustafa]

Isn´t this supposed to be with cold dilute acidifed KMnO4?

Dilute Cold* KMNO4

 

[AbbbbY]

From where have u brought this 9?

Number of primary hydrogens. I had to read the question several times to understand what 'game' the examiner was playing. He's taken a concept, twisted it, and asked it here.

 

[AbbbbY]

Dilute Cold* KMNO4

cold dilute, dilute cold. Whats the difference?!

 

[itallion stallion]

It will if you don't write ACIDIFIED.

Acidified K2Cr2O7 or (Cr2O7)2-/H+

What if I write heat in conditions where it is not mentioned in ms,but rest reagent and condition are complete,like if I want to make C6H5NH2 from C6H5NO2 and I use Sn +HCl and also heat so will writing heat negate the mark!

 

[itallion stallion]

Number of primary hydrogens. I had to read the question several times to understand what 'game' the examiner was playing. He's taken a concept, twisted it, and asked it here.

Really hard to digest,but Thanks aloot!

 

[Harsh Poddar]

I've made this site that can help you to quickly access past papers for a few common subjects. Try it out and please give feedback.

IGCSE: http://tinyurl.com/igcsepaper
AS & A Level: http://tinyurl.com/ciepaper

 

[Suchal Riaz]

I've made this site that can help you to quickly access past papers for a few common subjects. Try it out and please give feedback.

IGCSE: http://tinyurl.com/igcsepaper
AS & A Level: http://tinyurl.com/ciepaper

Thanks