Chemistry: Post your doubts here!

[sidbloom1995]

this one is from the same one as before, o/n 2010 p42
to me the reaction seem same going by the molecular formula and i cant say how the structure will be so can someone just give me a drawing of it's structure??

 

[hellangel1]

the same paper as

ok i get it but i used conc. H2SO4 with heat under reflux for ester reactions and since i saw this as esterification i did the same here ut was wrong!!
can u please tell y we cant use H2SO4?
Ohh and thank you for replying!

with acyl chlorides we get a much higher yield because HCl is evolved which is a gas and escapes from the reaction vessel causing equilibrium to move forward. So acyl chloride are preferred in esterification reactions

 

[syed1995]

Hi guys! Can you help me with this questions? Thank you in advance
View attachment 37249 View attachment 37249

NH4NO2 You need to come up with all possible molecular ions which can be formed from this..

Notice the peaks of A and B at 18 and 44. so form the compounds which can total to those two.

N - 14
O - 16
H - 1

For Compound A it's easy.. form the compounds which can total to 18.. H2O = 18 .. so answer for gas A will be H2O+, OH+, O+ (Remember only cations are present in the mass spectrometer)

For Compound B however it's difficult.. you know that one of the peaks is at 14 .. so that will be N+, another is at 16 so that will be O+ and one at 28 which will be N2+.. and at 30 it can be 14+16.. so NO+ so the compound has 2Ns and one O.. it's N2O! which cuz that equals 44 mass..

So answers for compound B will be N+,O+,N2+,NO+ and N2O+

Cheers

 

[syed1995]

PS: @everyone else who knows me/was here last year as well.. It's the end of march and I am back for the preparations.. do tag me if you have some EASY questions and good notes

 

[TheStallion-Reborn]

Can someone please explain what exactly is standard enthalpy change of atomisation?

 

[TheStallion-Reborn]

Can someone please help me with hybridisation?

 

[sidbloom1995]

with acyl chlorides we get a much higher yield because HCl is evolved which is a gas and escapes from the reaction vessel causing equilibrium to move forward. So acyl chloride are preferred in esterification reactions

i see thank you!

 

[sidbloom1995]

Can someone please explain what exactly is standard enthalpy change of atomisation?

standard enthalpy cahnge of atomisation is when one mole of gaseous atom are formed from element in there standard states!
suppose you have copper, Cu
naturally in the environment it exit as Cu(s)
but we convert it to gas by providing energy to it, thus it form Cu(g), the energy we provided is called the atomisation energy, and if we do it to a specific mass or mole of Cu(s) then it's called standard enthalpy change of atomisation!
so our equation will be Cu(s) ------> Cu(g)

 

[Pwetty Angel]

pleasee memberss!!
i really need revision sites for Chemistry stoichiometry!!!
moles iss really baddd.. i am not soo good in itt!

 

[ZaqZainab]

pleasee memberss!!
i really need revision sites for Chemistry stoichiometry!!!
moles iss really baddd.. i am not soo good in itt!

Helped me hope it helps you too
try http://studyguide.pk/

 

[mai jinn hun 2]

Can anyone help me with this questions?

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w05_qp_2.pdf
Question 5e, f and g

 

[Asad rehman]

I want quick answer for paper1 june 2007 q.9 only

 

[Pwetty Angel]

Helped me hope it helps you too
try http://studyguide.pk/

Thankyouu!!

 

[Pwetty Angel]

Can someone please explain Q5) c)i) of http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_2.pdf
Pleaseee

 

[Namehere]

Can someone please explain Q5) c)i) of http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_2.pdf
Pleaseee

Well ethanedial is simply a di aldehyde. Acidified potassium dichromate is used as an oxidising agent so will oxidize the aldehyde parts into two carboxylics.

 

[Pwetty Angel]

well owhh yeah i get it!! thankss Namehere

 

[sadiaali]

Please can anyone help me to explain the structure of ice. I had a bad chemistry teacher

 

[Faaiz Haque]

Question 5 A and 7 A i with explanation please.
Thanks

 

[sidbloom1995]

Can anyone help me with this questions?
View attachment 37561

in this one, H2PO4- ats like a base and donated electron and HPO4-2 acts as an acid
the trick is that when a buffer reacts with an acid or a base, the product include the reactent of the other (this is some thing that i have noticed and is not a given rule, watch in the example)

H+ + HPO4-2 ----------> H2PO4-
now
OH- + H2PO4- ---------> HPO4-2 + H2O

as for the part (iii)
you need to use the formula for acidic buffer solutions to find it's pH, which is
pH = pKa + log ( [salt]/[acid])
for pKa u use the value of 7.2, (sorry about this part im a little confused as to how to explain it, form what i remember, i took out the no. of moles of [H+] and used them again in pKa= (-log[H=]) equation and got 7.2 as answer so that's why you have to use 7.2, thought im still not 100% on that, sorry,)
can you give me the paper no. or this, i'll try solving it once more and see if i can answer it