Chemistry: Post your doubts here!

[Mayarzawaydeh]

http://onlineexamhelp.com/past-pape...evel-year-wise/9701-chemistry-a-as-level-2011

Hi.
can someone please help me with s11_qp_22 question 1 part c(ii) ?
thanks in advance.

 

[The Sarcastic Retard]

http://onlineexamhelp.com/past-pape...evel-year-wise/9701-chemistry-a-as-level-2011

Hi.
can someone please help me with s11_qp_22 question 1 part c(ii) ?
thanks in advance.

No. of moles of NaOH is 0.04 as we calculated earlier meaning (0.1 - x) = 0.04
Because alcohol was the reactant and equilibrium concentration of reactant is given by:
(initial concentration - x) so (0.1 - x) = 0.04 and
therefore x = 0.06
So concentretion of acid and alcohol is (0.1 - x) = (0.1 - 0.06) = 0.04

 

[Mahnoorfatima]

No. of moles of NaOH is 0.04 as we calculated earlier meaning (0.1 - x) = 0.04
Because alcohol was the reactant and equilibrium concentration of reactant is given by:
(initial concentration - x) so (0.1 - x) = 0.04 and
therefore x = 0.06
So concentretion of acid and alcohol is (0.1 - x) = (0.1 - 0.06) = 0.04

If you dont mind can you please explain this question to me?
https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9701_s12_qp_23.pdf
Question 5 part d? How are we supposed to know the compound. I get the next k2cr2o7 but I don't get what compounds isomers do I draw?

 

[The Sarcastic Retard]

If you dont mind can you please explain this question to me?
https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9701_s12_qp_23.pdf
Question 5 part d? How are we supposed to know the compound. I get the next k2cr2o7 but I don't get what compounds isomers do I draw?

Yet I have not started Organic, if you have any doubts regarding Physical and Inorganic ask me.
Sorry.

 

[Ahmed Aqdam]

If you dont mind can you please explain this question to me?
https://docs.google.com/viewerng/vi...wp-content/uploads/2012/11/9701_s12_qp_23.pdf
Question 5 part d? How are we supposed to know the compound. I get the next k2cr2o7 but I don't get what compounds isomers do I draw?

According to reactions in parts (a) and (b) F has functional groups CO2H and OH. Also it has a molecular formula C3H6O3. It will contain an alkene if it is dehydrated so C-C bond must be present. OH can be attached to any of these two Carbons. The rest of 4 Hydrogen atoms will also be attached to these Carbons. Possible compounds are HOCH2CH2CO2H and CH3CH(OH)CO2H.

 

[princess Anu]

can somebody do 20 d ii

 

[princess Anu]

I don't get when does an element form a dative bond
for example for ClF3 , I thought chlorine is donating its 3 lone pairs to 3 fluorine atoms :/ but that's not the case!! actually Cl is expanding its octet!
Now, how do we know when an element is expanding its octet and when an element is donating its lone pair?

 

[princess Anu]

J 2013 p21 Q5a
in this part, h2 with Ni catalyst is actually reducing an aldehyde to primary alcohol :O
Does it happen always? will that mean it can reduce carboxylic acid and ketone too??

 

[qwertypoiu]

I don't get when does an element form a dative bond
for example for ClF3 , I thought chlorine is donating its 3 lone pairs to 3 fluorine atoms :/ but that's not the case!! actually Cl is expanding its octet!
Now, how do we know when an element is expanding its octet and when an element is donating its lone pair?

This Question came in 2013 J

For two atoms to form a dative bond, one of them must have a lone pair of electrons, and the other an empty orbital. In the case of ClF3, yes chlorine may have three lone pairs of electrons but Fluorine does NOT have an empty orbital to accept the lone pair being offered. So it could not have been dative bond

 

[The Sarcastic Retard]

can somebody do 20 d ii

http://forums.sgclub.com/singapore/chemistry_redox_question_338590.html

 

[Mayarzawaydeh]

can somebody do 25 d ii

I don't get when does an element form a dative bond
for example for ClF3 , I thought chlorine is donating its 3 lone pairs to 3 fluorine atoms :/ but that's not the case!! actually Cl is expanding its octet!
Now, how do we know when an element is expanding its octet and when an element is donating its lone pair?

I assume this is a simple concept. To know whether an atom donates a pair of electrons or shares them to expand it's octet, you have to think about each atom and how many electrons it requires to complete it's octet.
the atom that donates it's pair of electrons has to have at least one pair of lone pair of electrons after it has formed the bond.
also you have to know, that in a dative bond, the electron donor atom donates electrons in pairs. (in the case you mentioned, 3 electrons donated are not in pairs. hence in this case chlorine has to share those 3 electrons with 3 fluorine atoms to expand it's octet.) if an atom has those qualities metioned then in this case it will donate a lone pair instead of expanding it's octet.

you can look at other similar example to help you,

• like Al2Cl6, ( in this case there is no octet expansion taking place)

here each aluminium atom is covalently bonded with 3 chlorine atoms , while at the same time it's accepting a pair of electrons from a forth chlorine atom,,, take a look at the fourth chlorine atom, (as mentioned before the atom donating the pair of electrons has to have at least one pair of electrons after forming the bond, at the same time it donates the electrons in pairs.)
I hope this answers your question

 

[princess Anu]

I assume this is a simple concept. To know whether an atom donates a pair of electrons or shares them to expand it's octet, you have to think about each atom and how many electrons it requires to complete it's octet.
the atom that donates it's pair of electrons has to have at least one pair of lone pair of electrons after it has formed the bond.
also you have to know, that in a dative bond, the electron donor atom donates electrons in pairs. (in the case you mentioned, 3 electrons donated are not in pairs. hence in this case chlorine has to share those 3 electrons with 3 fluorine atoms to expand it's octet.) if an atom has those qualities metioned then in this case it will donate a lone pair instead of expanding it's octet.

you can look at other similar example to help you,

• like Al2Cl6, ( in this case there is no octet expansion taking place)

here each aluminium atom is covalently bonded with 3 chlorine atoms , while at the same time it's accepting a pair of electrons from a forth chlorine atom,,, take a look at the fourth chlorine atom, (as mentioned before the atom donating the pair of electrons has to have at least one pair of electrons after forming the bond, at the same time it donates the electrons in pairs.)
I hope this answers your question

But I said 3 LONE PAIRs of Electron :s
do you mean to imply, by the al2cl6 example, that the element forming a dative bond must have lone pair after it
has formed the dative bond? :O

 

[Metanoia]

I don't get when does an element form a dative bond
for example for ClF3 , I thought chlorine is donating its 3 lone pairs to 3 fluorine atoms :/ but that's not the case!! actually Cl is expanding its octet!
Now, how do we know when an element is expanding its octet and when an element is donating its lone pair?

Each F only needs one more electron, they can't accept a lone pair from the Cl atom.

One simple guideline is to explore the possibility of a covalent bond first before considering using dative bonds.

 

[Metanoia]

J 2013 p21 Q5a
in this part, h2 with Ni catalyst is actually reducing an aldehyde to primary alcohol :O
Does it happen always? will that mean it can reduce carboxylic acid and ketone too??

Ni/H2 reduces alkenes, aldehydes, ketones and nitriles. But not carboxylic acid.

To reduce carboxylic acid, you need to use LiAlH4.

 

[Awesome12]

http://studentbounty.com/pastpapers.../Chemistry (9701)/2011 Jun/9701_s11_qp_12.pdf

Question 26?

 

[Mayarzawaydeh]

http://studentbounty.com/pastpapers/Cambridge International Examinations (CIE)/International AS and A Level/Chemistry (9701)/2011 Jun/9701_s11_qp_12.pdf

Question 26?

the Answer is D.
possible isomers are:
1. CH2=CHCH2CH2CH3
2. CH3CH=CHCH2CH3 <--- the cis isomer.
3. CH(CH3)=CH(C2H5) <--- the trans isomer.
4. CH2=C(C2H5)CH3
5. CH2=C(CH3)CH2CH3
6. CH3C(CH3)=CHCH3

 

[Sarosh Jameel]

SOMEONE !

 

[princess Anu]

what will be the structure of ClF4-?

Each F only needs one more electron, they can't accept a lone pair from the Cl atom.

One simple guideline is to explore the possibility of a covalent bond first before considering using dative bonds.

 

[princess Anu]

How to name organic compounds with more than one functional group?
which functional groups are chosen as to give them the least number? and is it necessary for both or all of the functional groups to be on the longest chain ?

 

[princess Anu]

SOMEONE !

30 C?
28 D?
37 A?

and the last one D?