Chemistry Paper 21 discussion

[Ariel Robert]

There wasn't an alcohol in the organic compound as far as I recall. Crotonaldehyde it was :/

As for percentage purity, I got 43.3% :/

I even got 43.3% because of the mole ratio 1:2 if you got something 80% that's wrong, because you did not take the mole ratio...

The equation is (NH4)2SO4 + 2NaOH = 2NH3 + Na2SO4 + 2H2O

My Equation was wrong but the percentage was correct

My Equation --> (NH4)2SO4 + 2NaOH = NH3 + NaHSO3 + H2O

I didnt balance it because time was up... but i knew that the mole ratio was 1:2 because I did this equation long back...

 

[Ariel Robert]

Though it was a very easy paper... Threshold might be high...

 

[Adorkableme]

i got +90.5 KJ/mol

the enthalpy change of formation is -ve so we had to put a -ve sign there....my answer was +ve but the correct sign was -ve.....

 

[HubbaBubba]

the enthalpy change of formation is -ve so we had to put a -ve sign there....my answer was +ve but the correct sign was -ve.....

Enthalpy change of Formation can be both negative and positive. The equation doesn't work if you input -90.5 instead of +90.5

 

[Manobilly]

the enthalpy change of formation is -ve so we had to put a -ve sign there....my answer was +ve but the correct sign was -ve.....

it is positive!

 

[HubbaBubba]

Yup, it was a bit of a sneaky question, because with the cycle you get 362, but you had to divide it by 4.

Also, which element forms an oxide that's a reducing agent? Only one I didn't know and so I put down Calcium. Otherwise, this test was easy.

I did a quick research on google. The answer can be Aluminium, Sulphur, or Calcium

 

[HubbaBubba]

the enthalpy change of formation is -ve so we had to put a -ve sign there....my answer was +ve but the correct sign was -ve.....

The equation was 4x + 6(-242) + 4(-42) = -906
So x = +90.5
If you input -90.5 the equation cannot add up to -906

 

[1357913579]

I did a quick research on google. The answer can be Aluminium, Sulphur, or Calcium

wasnt the question asking oxidising agent?

 

[Ariel Robert]

wasnt the question asking oxidising agent?

no it was reducing agent

 

[Jisu]

what was the no. of electrons around chlorine in ClF3

2 lone pairs and the rest bonding pairs

 

[Jisu]

I did a quick research on google. The answer can be Aluminium, Sulphur, or Calcium

I wrote calcium x)

 

[Jisu]

What about the organic stuff...there were all 4 of the mechanisms right?? The one where we had to write the mechanism and reagents
What about for the last question with cold n hot manganate ions..did u get diol first and then ketones were formed??

 

[hela]

There wasn't an alcohol in the organic compound as far as I recall. Crotonaldehyde it was :/

As for percentage purity, I got 43.3% :/

i wrote my answer as 43,29% do i lose the mark ?

 

[iKhaled]

Someone pls explain the Clf3 and ClBr3 question..the difference in their boiling point ?

 

[Rain]

I even got 43.3% because of the mole ratio 1:2 if you got something 80% that's wrong, because you did not take the mole ratio...

The equation is (NH4)2SO4 + 2NaOH = 2NH3 + Na2SO4 + 2H2O

My Equation was wrong but the percentage was correct

My Equation --> (NH4)2SO4 + 2NaOH = NH3 + NaHSO3 + H2O

I didnt balance it because time was up... but i knew that the mole ratio was 1:2 because I did this equation long back...

Alhumdulilah It took me some time to get this equation. I left the question in the start and came back after completing the rest of the paper.

43.3% check.

 

[Manobilly]

A

Alhumdulilah It took me some time to get this equation. I left the question in the start and came back after completing the rest of the paper.

43.3% check.

Alhamdulillah did the same thing

 

[ali khan saaed]

2 lone pairs and the rest bonding pairs

there is a dative bond ..

 

[hady94]

What was the answer for the difference in boiling points between ClF3 and BrF3 ?
Is it to do with the difference in size and strength of van der Waals ?

 

[ali khan saaed]

what is answer for 1 mole question calculation part

 

[salvatore]

One of my friends also got 80% because he did something else in the (ii) of the moles question. I'm sure there's an E.C.F on the question, so as long as you showed your working and it's correct according to your answers, then they'll just minus you one or two marks!

Damnn! I just realised.. I hadn't balanced the second equation right