Chemistry: Post your doubts here!

[Falconwing]

I had no idea there was a connection! Thanks alot ^^

 

[Kool boy]

Any idea about paper 32

 

[Xaptor16]

Convert the masses of ethanol and ethanoic acid to moles to figure out the limiting reagent.

Limiting reactant is acid, 0.5 moles. Expected moles of ester is thus 0.5 moles, 44g.

%yield = 22/44 = 50%

thankyou

 

[Xaptor16]

n of alcohol = 30/46
n of acid = 30/60
limiting reagent is acid since its no of mole is smaller
so mass of theoretical yield of ester - 30/60 x 88 = 44
percentage = 22/44 x 100% = 50%

thanks!

 

[princess Anu]

Yes.... princess anu......all the answers are correct.............but can u explain?

last one : the rate increases at first as products are being formed ..(products act as catalyst here). but soon all of the substrate gets used up, products r no longer being formed therefore rate finally decreases.

21 A & B are wrong. in D, since v r using aqueous HCL there is a possibility of lone pair on O of H2O attacking the carbocation instead of the Cl.. therefore it may not give the best yield

27: I wasn't sure about it.. though I recognised the repeating unit ( I have marked it on the picture) & then I thought the groups on both ends of the repeating unit must possess a double bond in order to polymerise.

 

[princess Anu]

Q38 why is 2 wrong?

Q8 why do we need pH 7? both Al(no3)3 & Ba(No3)2 are neutral compounds right.. so even extremely high/low pH should not affect them? :s

 

[princess Anu]

help with this please

 

[princess Anu]

how to do it?

 

[princess Anu]

2 moles of water are formed, and the arrow is pointed in the correct direction, so it is +2 multiplied by the enthalpy of formation of water.

had they given an option like.. ' -2 * enthalpy change of combustion of H2'.. wud that be correct?

 

[nehaoscar]

Wouldn't a lower temperature increase the rate of the forward reaction since it's exothermic? So why is it A instead of D??

Did you find out why? If so please can you explain to me too?

 

[nehaoscar]

How to do this one?
I form the table but then I don't know what to do (which values for P and Q?)

 

[Autumn98]

someone please help me with this.. answer and reason? asap

 

[Mathemagical]

someone please help me with this.. answer and reason? asap

The answer is A.

From the diagram and the arrow showing the enthalpy change of formation, we can conclude that the bottommost layer is CO2(g).

Thus, the second from bottom level has to be Option C, which shows the elements in their standard states. Working our way upwards, we can see that the change from Option B to Option A is an enthalpy change of vaporisation, which is positive. Therefore, A is the top level.

 

[Mathemagical]

had they given an option like.. ' -2 * enthalpy change of combustion of H2'.. wud that be correct?

No, it would not be correct. The signs + and - are very important in Hess Law reactions, and it is important to keep them in mind while attempting questions of this sort.

 

[nehaoscar]

What bondings do each contain?

 

[nehaoscar]

Have i marked the dipoles correctly? And why B? why not the others?

 

[Mathemagical]

View attachment 54304
How to do this one?
I form the table but then I don't know what to do (which values for P and Q?)

This requires a bit of trial and error. The answer is D.

 

[Mathemagical]

View attachment 54310
Have i marked the dipoles correctly? And why B? why not the others?

In C and D, the dipoles sort of "cancel out" each other so the overall dipole will not be as large as the one in B.

 

[nehaoscar]

Wouldn't A form H2O2 ?
And if not what will it form? like what would the equation be?

 

[nehaoscar]

This requires a bit of trial and error. The answer is D.

Thanks! So it's always trial and error? There's no way to work it out directly right?