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last SG · 2015-08-19T22:54:00+00:00

Topic : atomic radius Hi! This is from singapore cambridge nov a level exam year 2010,Paper 1 qn 1Qn: which element has the largest atomic radius?BrKKrScSo...

Flying grenade SG

For FO2 to have single bonds between the F and two O atoms, F will gain a 2+ charge and each O atom with gain a -ve charge, and this separation of charge is destabilizing, since F is more electronegative than O.

Wouldn't '+' and '-' attract?

UltimaOnline SG

Mr heng may i ask u, is the one drawn with pencil correct

https://www.dropbox.com/s/avl731ngdwlyxmb/20151105_134421.jpg?dl=0

Then, if one were to draw the 9 e- ard cl atom, would it be wrong?

Edited : Yes, my typo, 1.5 lone pairs not 2.5 lone pairs.

I'll only reply to your last qn. For all the other qns, you need to come for my tuition to properly discuss and understand it. Furthermore, there's no time to address it now liao, it's best not to confuse yourself further just a few hours away from the A level exam.

Yes, your doubly bonded ClO2 is acceptable (unless the Cambridge qn specified conditions such as the presence of a dative bond, etc), and is actually 1 of the resonance contributors for ClO2 (the only one without separation of formal charges), no worries.

Flying grenade SG

SOLUBILITY OF SULFATES, CARBONATES, NITRATES DECREASES DOWN THE GROUP

Whereas SOLUBILITY OF HYDROXIDES INCREASES DOWN THE GROUP

How to account for this? I only know this

Less exothermic DelHsoln signifies a less soluble salt

Less exo DelHhyd decreases solubility

Less exo L.E. enhances solubility

Flying grenade SG

Mr heng i wan come ur tuition !!!

Mr heng wont confuse lah i love to seek knowledge

Wont confuse, i understand and absorbed everything you've posted hehe

Flying grenade SG

2010 p3 qn 4 gii

Photo is here

https://www.dropbox.com/s/morxcgb8519dx60/20151105_145329.jpg?dl=0

How can secondary alcohol oxidise to Carboxylic acid??

Thought secondary alcohol can only oxidise to ketone at maximum?

Flying grenade SG

Do we have to specify/indicate the polarity of an electrolytic cell /electrochemical cell?

E.g. 2010 p3 qn 5

When do we have to?

UltimaOnline SG

SOLUBILITY OF SULFATES, CARBONATES, NITRATES DECREASES DOWN THE GROUP

Whereas SOLUBILITY OF HYDROXIDES INCREASES DOWN THE GROUP

How to account for this? I only know this

Less exothermic DelHsoln signifies a less soluble salt

Less exo DelHhyd decreases solubility

Less exo L.E. enhances solubility

No time liao to bother with this (and you need to come for my tuition to discuss this properly, it's too inefficient back and forth on an online forum). But for those who feel they're prepared for tmrw's paper liao, and are keen on understanding this (it's *possible* Cambridge can ask this), can read : http://www.chemguide.co.uk/inorganic/group2/problems.html

UltimaOnline SG

Do we have to specify/indicate the polarity of an electrolytic cell /electrochemical cell?

E.g. 2010 p3 qn 5

When do we have to?

Wah lau eh, if in doubt just specify lor! If the qn need u to specify, it'll say so mah!

UltimaOnline SG

2010 p3 qn 4 gii

Photo is here

https://www.dropbox.com/s/morxcgb8519dx60/20151105_145329.jpg?dl=0

How can secondary alcohol oxidise to Carboxylic acid??

Thought secondary alcohol can only oxidise to ketone at maximum?

There are only 3 ways for a ketone to be further oxidized :

If it's part of a benzene ring side chain (with a benzylic H atom).

If you use a chemical oxidizing agent stronger than KMnO4, eg. concentrated HNO3.

If you burn it.

Flying grenade SG

You rock my world,

Thank you. Angel sent from heaven

Sludge man!

UltimaOnline SG

I’m logging off this forum at 9pm sharp until tmrw afternoon. Any serious and urgen qns, you guys (ie. JC students taking A levels tmrw) better post now. I won’t reply any posts after 9pm. Tell u first hor.

UltimaOnline SG

Logging off for tonight liao. Cya guys tomorrow here in this forum after P2 to discuss the P2 questions! Have fun! ;D

Flying grenade SG

Since amide and ester can react with both naoh and hcl, can it be said that they are amphoteric /amphiprotic?

UltimaOnline SG

No.

Flying grenade SG

When/what can say amphoteric/amphoprotic species

UltimaOnline SG

When/what can say amphoteric/amphoprotic species

When the species (eg. HCO3-) can both donate and accept a proton in an acid-base reaction. An ester or amide can only *kena hydrolyzed* by acid or alkali in a *hydrolysis* reaction, not acid-base reaction.

UltimaOnline SG

When/what can say amphoteric/amphoprotic species

And it's "amphiprotic" lah, still write what "amphoprotic" leh, make Cambridge laugh at Singapore students.

Edited : ok I noticed you spelled it correctly in an earlier post, so it's just your typo. Notwithstanding, typos can still make Cambridge laugh at Singapore students.

UltimaOnline SG

Oh, in case you're wondering (or if Cambridge decides to play punk and asks) "What's the difference between "amphoteric" and "amphiprotic"?", go read Jim Clark's http://www.chemguide.co.uk/physical/acidbaseeqia/theories.html

Bonus : If Cambridge asks "What's the difference between "amphoteric" and "amphiprotic"? Illustrate your explanation with an example of a species that is amphoteric but not amphiprotic."

Well, Al2O3 is an example of a species that is amphoteric but not amphiprotic. Can you figure out why? ;)

Vitalitylx SG

Hi for MJC Prelim 2014 P2/Q3b(iii)

the answer written for the oxidation state of cobalt in salt A is +4, but I cannot see why? From drawing the structure shouldn't it be 0?

UltimaOnline SG

Hi for MJC Prelim 2014 P2/Q3b(iii)

the answer written for the oxidation state of cobalt in salt A is +4, but I cannot see why? From drawing the structure shouldn't it be 0?

The question didn't even ask for the OS of Co in salt A, only in salt B. So if the question didn't ask, how can there be an answer (for a question that wasn't asked)? But yes you're right, the OS of cobalt in salt A is 0 (formal charge 4-) and in salt B is +3 (formal charge 3-).

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