Chemistry: Post your doubts here!

[PANDA-]

hmm i think that this question is the question where it says no oxygen atom is attached to carbon because if this is the case then ur answer is wrong plus ur answer is not fully displayed so it is wrong yeah. is this the question where it says no oxygen is attached to carbon=carbon double bond?

Yes! That's it..
I didn't fully read the question My bad.

You have the eyes of a hawk

 

[MaxStudentALevel]

if it didn't specify then i am sure it is accepted in any form but maybe since professional examiners set up the marking scheme for A levels then they draw the structures in skeletal formulas most of the time

Makes sense. Ithink I better ask a teacher for a confirmed opinion

 

[daredevil]

I want to know how we calculate the kc like in questions may/June 2007 question. 2c

Kc is calculated using the formula
([C]^c x [D]^d )/([A]^a x ^b)

for a reaction: -
aA + bB --> cC + dD

where the small letters represent the number of moles of the substances (capital letters are substances)
x is the sign of multiplication
and do not use round brackets at all!! i used them just to show that all the products were in the numerator and theproducts are all in denominator

 

[knowitall10]

HEY GUYS pleasssssse answer this for me:

STRUCTURAL FORMULA = OH(CH2)4OH for example
Right?
SKELETAL= OH/\/\/OH
Right?
DISPLAYED is where you show the bonds.

BUT in the A2 MS all organic comounds are given I skeletal? When it says "DRAW THE STRUCTURES"
Does that not mean draw structural formulae?

Just draw what's easy for you when they don't specify. Examiner bara hadharam aadmi hai

 

[PANDA-]

One more thing iKhaled
Do we have to show all bonds when drawing a displayed formula?

Like if there's a big compound, can we draw CH3 as CH3 or do we have to draw it with all bonds?

 

[knowitall10]

Yes! That's it..
I didn't fully read the question My bad.

You have the eyes of a hawk

lol

 

[iKhaled]

One more thing iKhaled
Do we have to show all bonds when drawing a displayed formula?

Like if there's a big compound, can we draw CH3 as CH3 or do we have to draw it with all bonds?

if the question says "fully displayed" then yes u have to show every single bond or u will lose the mark for not showing it displayed. this applies more to optical isomerism

 

[MaxStudentALevel]

Hey can anyone step by step explain Q1 (c) for MJ12-41 ??
I always get SIMPLE lattice energy or enthalpy change questions in general wrong :/
I'd be forever greatfuk (

 

[knowitall10]

Hey can anyone step by step explain Q1 (c) for MJ12-41 ??
I always get SIMPLE lattice energy or enthalpy change questions in general wrong :/
I'd be forever greatfuk (

hahaha *grateful you mean.. that sounds wrong

 

[MaxStudentALevel]

hahaha *grateful you mean.. that sounds wrong

HAHAHAH OMG LOLLLL

 

[PANDA-]

hahaha *grateful you mean.. that sounds wrong

LOL.

 

[Jinkglex]

Any other questions or queries guys?

BTW i have a question myself. Does reactivity depend on cation SIZE or charge and if so how does it depend on it? And also, what is the difference between ALKALI and BASE?

 

[knowitall10]

Any other questions or queries guys?

BTW i have a question myself. Does reactivity depend on cation SIZE or charge and if so how does it depend on it? And also, what is the difference between ALKALI and BASE?

Dude, you in AS or A2?
and not all alkali are bases but all bases are alkali. This is my IGCSE knowledge which always confuses me... maybe u understand it
Reactivity depends on numerous factors that are affected by size and charge.. for eg ionisation energy..or electronegativity.. am i right? It's been a while since i last looked at this chapter.. its about time i start revising

 

[Jinkglex]

Im in A2 why do you ask? and alright thanks I was just confused because i keep involving Lattice energy in here, which is strictly A2

 

[PANDA-]

Dude, you in AS or A2?
and not all alkali are bases but all bases are alkali. This is my IGCSE knowledge which always confuses me... maybe u understand it
Reactivity depends on numerous factors that are affected by size and charge.. for eg ionisation energy..or electronegativity.. am i right? It's been a while since i last looked at this chapter.. its about time i start revising

You got it wrong there, all alkali are bases bot not all bases are alkaline. This is because alkali's are bases which are dissolved in water, like NaOH(aq) for example.
Reactivity mainly depends on the effective nuclear charge, atomic radius, and molar mass (not really sure about molar mass lol).

 

[Jinkglex]

And check this out :

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s03_qp_2.pdf
http://papers.xtremepapers.com/CIE/.../Chemistry (9701)/9701_s03_ms_1+2+3+4+5+6.pdf

isnt the MP graph for question 4A wrong? Since there is a slight increase from P to S in melting point?

 

[Jinkglex]

Molar mass only plays a part in diffusion rate and thus it KIND of does affect reactivity, but not really

 

[knowitall10]

Im in A2 why do you ask? and alright thanks I was just confused because i keep involving Lattice energy in here, which is strictly A2

Oh i was asking cuz depending on that, i'd ask you my questions... firstly... i do not understand how on earth to calculate the enthalpy change using bon enthalpies- more precisely i'm always confused which side is bond breaking and which is bond forming... i know this is AS stuff but i hate the AS part that comes in p4... the manhoos examiners can't make it any harder :/

 

[knowitall10]

You got it wrong there, all alkali are bases bot not all bases are alkaline. This is because alkali's are bases which are dissolved in water, like NaOH(aq) for example.
Reactivity mainly depends on the effective nuclear charge, atomic radius, and molar mass (not really sure about molar mass lol).

thanks Panda... i'm ashamed to mention i'm in A2 now

 

[Manobilly]

Kc is calculated using the formula
([C]^c x [D]^d )/([A]^a x ^b)

for a reaction: -
aA + bB --> cC + dD

where the small letters represent the number of moles of the substances (capital letters are substances)
x is the sign of multiplication
and do not use round brackets at all!! i used them just to show that all the products were in the numerator and theproducts are all in denominator

Can you show the full working of the question.