Chemistry Paper 21 discussion

[HubbaBubba]

Since 24 hours is up, I'm guessing we can discuss the answers ^_^ How much did you guys get in q1 - the percentage purity?

 

[shahed oly]

I got 28 percent

 

[red_angel]

I got 40 something % can't remember :/ What did you get?

 

[HubbaBubba]

44.6% after rounding to 3sf

What about q2? Did you get +90.5 KJ/mol in the hess law question? ^_^

 

[shahed oly]

i got +90.5 KJ/mol

 

[shahed oly]

what was the no. of electrons around chlorine in ClF3

 

[red_angel]

Yes yes something like that! Yup got that exact answer. Was worried about the positive sign but I thought if that's the answer I'm getting then I'm gonna leave it like that. Alhamdulillah

 

[IbtiCool]

Hey. For Question 1, I got 44+ something purity. Can't remember. And the Standard Enthalpy Change of NO was +90 something. This question caused a lot of issues because of it's sign What about the 2nd last question? What was the reaction of that alkene with PCL3

 

[schelsinger]

no reaction

 

[schelsinger]

i accidentally broke the double bond and placed 2 chlorine atoms in there

 

[HubbaBubba]

what was the no. of electrons around chlorine in ClF3

I got 10 electrons i think? It wasn't a normal number.

Hey. For Question 1, I got 44+ something purity. Can't remember. And the Standard Enthalpy Change of NO was +90 something. This question caused a lot of issues because of it's sign What about the 2nd last question? What was the reaction of that alkene with PCL3

We were supposed to leave the double bond and replace the OH with Cl. I didn't do that though T_T Made it a halogenoalkane with an OH.

 

[salvatore]

Everyone's getting 30-40% for the impurity question.. I got 85%!!
I just hope I don't lose all the marks in the question..

 

[HubbaBubba]

Everyone's getting 30-40% for the impurity question.. I got 85%!!
I just hope I don't lose all the marks in the question..

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!

 

[iKhaled]

hay guys the last question the last part of it when i broke the c=c double bond i didn't fully oxidise the organic compound to acid i only did to aldehyde..is it acceptable or i had to do complete oxidation ?

 

[n00bfi]

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% :/

 

[Manobilly]

What was the enthalpy change for NO and the percentage. For the fertilzer?

 

[HubbaBubba]

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% :/

Sorry I got confused ^_^ You're right it's NO REACTION. It's okay me and my classmates all got differing answers ranging from 1% to 2%. Depends if you rounded it up throughout the parts or only at the end. Personally I rounded it to 3 sf for each answer, getting 44.6 as my final answer.

What was the enthalpy change for NO and the percentage. For the fertilzer?

Enthalpy change is +90.5 (Triple checked, and it works in the equation), and I got percentage purity as 44.6% Your answer might vary by 0.5-2% if you did it correctly

 

[n00bfi]

Enthalpy change is +90.5 (Triple checked, and it works in the equation), and I got percentage purity as 44.6% Your answer might vary by 0.5-2% if you did it correctly

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.

 

[n00bfi]

what was the no. of electrons around chlorine in ClF3

It was 10, two lone pairs and 3 bonding pairs with Fluorine.

 

[Manobilly]

Sorry I got confused ^_^ You're right it's NO REACTION. It's okay me and my classmates all got differing answers ranging from 1% to 2%. Depends if you rounded it up throughout the parts or only at the end. Personally I rounded it to 3 sf for each answer, getting 44.6 as my final answer.

Enthalpy change is +90.5 (Triple checked, and it works in the equation), and I got percentage purity as 44.6% Your answer might vary by 0.5-2% if you did it correctly

Alhamdulillah I got the same answers: D my friend when I came out most of them told me the that the enthalpy change they got is 300 smthng,I didvide that 300 by 4 to get 90.5.and yeah the no reactiom was pcl3