Chemistry: Post your doubts here!

[h4rriet]

="h4rriet

q10 same ppr

Draw a Hess cycle.

 

[kiran11]

Can't see the question because your link doesn't work.

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q10, i have confusion btwn B and C

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q10, i have confusion btwn B and C

B's dipole is 6 multiplied by the dipole of C-H, whereas C's dipole is 2 multiplied by the dipole of C-Cl.

 

[cute97]

22. Ethyl propanoate will give ethanol and sodium propanoate when hydrolysed with NaOH. Find the molecular masses of both, and then find the % by mass. For example, to find the % by mass of ethanol, do (mass by ethanol)/(mass of ethanol + sodium propanoate).
23. Yes, but you have to take into account the number of C atoms as well.

okk got it thank you very much frnd

 

[cute97]

They're saying that the compound reacts with Na to give a 3+ charged ion. Only OH and CO2H react with Na to give a 1+ charged ion, so there must be 3 functional groups, either CO2H or OH. When NaOH reacts, a compound with a 1+ charge is produced by CO2H only, not OH. That means there is only ONE CO2H in the compound we're talking about. So there is ONE CO2H and TWO OH groups, that makes it 3 overall. So they can react with Na to give a 3+ charged ion and with CO2H to give a 1+ charged ion.

ooohh okkk thankss

 

[Jiyad Ahsan]

yes but how we will choose btwn C and B option of the same question?

the Cl and the O cancel each others effects somewhat as they both are quite electronegative.. in option C,
while in option B the O side becomes electronegative quite easily, no resistance from the CH4 to become electro-positive whatsoever

the correct link..
papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s12_qp_12.pdf

 

[Alice123]

Construct the balanced equation for the reaction between N2 and H2. 120-96 kg of H2 is used. Use mole ratios.

in that case 8 moles of N2 will react with 24 moles of H2 and 16 moles of NH3 are produced....
so mass of NH3 wud be 16* Mr of NH3 ie 272 :/ please help me out

 

[Dr.MMM]

Thank you so much

 

[h4rriet]

Can you do it for me ?

 

[cute97]

i think we will have products ethanoic acid and propanol

ummm noo i think sodium ethanoate and propanol i tried it and i got correct answer cz in the ques they used an alkali so salt of the acid is formed instead of an acid COONa

 

[kiran11]

B's dipole is 6 multiplied by the dipole of C-H, whereas C's dipole is 2 multiplied by the dipole of C-Cl.

i am sorry but i still have confusion whr did the 6 and 2 came from to multiply with c-h nad c-cl

 

[Aries_95]

Can you do it for me ?

apart form drawing the Hess's cycle, try using this method:
C3H6O+4O2---->3CO2+3H2O
Enthalpy change of combustion of propanone is the enthalpy change of reaction. and the enthal of formation of an element is always zero.
(-1786)+(Enthalpy of formation of propanone)= (3x enthalpy of combustion of C)+ (3x enthalpy of H2)
(-1786)+(X)= (3x-394)+(3x-286)
(-1786)+X=(-1182)+(-858)
(-1786)+X=-2040
X=-254 kj/mol
Answer is C.
Plz tell me is this answer right?

 

[kiran11]

ummm noo i think sodium ethanoate and propanol i tried it and i got correct answer cz in the ques they used an alkali so salt of the acid is formed instead of an acid COONa

i didnt see NaOH, sorry :-s

 

[darkxangel]

apart form drawing the Hess's cycle, try using this method:
C3H6O+4O2---->3CO2+3H2O
Enthalpy change of combustion of propanone is the enthalpy change of reaction. and the enthal of formation of an element is always zero.
(-1786)+(Enthalpy of formation of propanone)= (3x enthalpy of combustion of C)+ (3x enthalpy of H2)
(-1786)+(X)= (3x-394)+(3x-286)
(-1786)+X=(-1182)+(-858)
(-1786)+X=-2040
X=-254 kj/mol
Answer is C.
Plz tell me is this answer right?

Yes, the answer is C and thankyou

 

[Dr.MMM]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q28?

 

[darkxangel]

Thankkks

 

[Aries_95]

Yes, the answer is C and thankyou

Welcome
Hope you understand

 

[h4rriet]

i am sorry but i still have confusion whr did the 6 and 2 came from to multiply with c-h nad c-cl

2 C-Cl bonds and 6 C-H bonds (because there are 2 CH3 groups and each group contains 3 C-H bonds; draw a displayed formula if it still isn't clear).

 

[kiran11]

2 C-Cl bonds and 6 C-H bonds (because there are 2 CH3 groups and each group contains 3 C-H bonds; draw a displayed formula if it still isn't clear).

ok thank u i got it now. thank u so much!

 

[cute97]

ANYONE PLS
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q4, Q17,Q23
thanks in advance plz answer