Edexcel IAL Chemistry Unit 2 (WBIO2) / June 10th 2016

Original post by omar5478

I absolutely hate this paper. Although I am pretty confident about getting a high A in Unit 1 and 3, I am barely getting an A in the past papers of this unit (losing 15-20 marks) which is really frustrating. I lose a ton of marks from the practical stuff and the one markers , so do you have any tips for those ??

Could you explain question 3 and 4 in the June 2014(R) paper as well ?? I am at a loss with these equilibrium questions.

3a) - A decrease in temperature always favors the exothermic side. Since the enthalpy of the reaction is negative ( exothermic reaction), the equilibrium shifts to the right side, hence color change is goes dark purple.

3b) - An increase in pressure favors the side with fewer molecules. The reactants side has 2 molecules whereas products side has 4 molecules (2 hydrogen and 2 iodine molecules), therefore the equilibrium shifts to the left side and goes dark purple.

4a) - A solution of I2 dissociates to give ions in a solution of NaOH as it reacts with it, hence the equilibrium shifts to the right and the mixture goes lighter.

Hope that helps. :smile:

Reply 5

Original post by Sandy_Vega30

3a) - A decrease in temperature always favors the exothermic side. Since the enthalpy of the reaction is negative ( exothermic reaction), the equilibrium shifts to the right side, hence color change is goes dark purple.

3b) - An increase in pressure favors the side with fewer molecules. The reactants side has 2 molecules whereas products side has 4 molecules (2 hydrogen and 2 iodine molecules), therefore the equilibrium shifts to the left side and goes dark purple.

4a) - A solution of I2 dissociates to give ions in a solution of NaOH as it reacts with it, hence the equilibrium shifts to the right and the mixture goes lighter.

Hope that helps. :smile:

Wait, what ?? Doesn't pressure favor the side with less moles (not molecules) ?? Moreover, doesn't 2HCL contain 4 molecules as well ??

Reply 6

Sandy_Vega30

OP

Original post by omar5478

Wait, what ?? Doesn't pressure favor the side with less moles (not molecules) ?? Moreover, doesn't 2HCL contain 4 molecules as well ??

Oh god! So sorry! I just realized my mistake! Yes, pressure favors the side with fewer moles since product side has only one mole and reactant side has 2 moles, the equilibrium shifts to the right hand side to give a dark purple solution.

Spoiler

Reply 7

Original post by Sandy_Vega30

Oh god! So sorry! I just realized my mistake! Yes, pressure favors the side with fewer moles since product side has only one mole and reactant side has 2 moles, the equilibrium shifts to the right hand side to give a dark purple solution.

Spoiler

Maybe I am just turning blind by this point, but don't both sides contain 2 moles of gases(2 of HCL on the reactants side, 1 of H2 and 1 of Cl2) ? What am I not getting here ?

Thanks for the compliment btw, I am still not good enough to secure that A though.

(edited 7 years ago)

Reply 8

alevels2k17

14

I srsly hate this paper so much, and im so unmotivated to revise for it ughhhh. Unit 1 is way waaaaay better than this.

Reply 9

Sandy_Vega30

OP

Original post by omar5478

Maybe I am just turning blind by this point, but don't both sides contain 2 moles of gases(2 of HCL on the reactants side, 1 of H2 and 1 of Cl2) ? What am I not getting here ?

Thanks for the compliment btw, I am still not good enough to secure that A though.

Oh yeah, well if I were to answer this question I would choose A because pressure has no effect on an equilibrium that has equal moles on both sides. But I don't know why the answer is D. Give me sometime, I'll ask my teacher and let you know soon.

As for the tips, especially the one markers. Always answer in context to the question. Try and understand or better, visualize the question. Any one marker following that question would probably sound like : Why was so and so used to blah blah blah? In this case, try and analyse the experiment. This may give you lots of sensible points. Try learning all the diagrams for distillation etc. Good luck!

Reply 10

Original post by Sandy_Vega30

Oh yeah, well if I were to answer this question I would choose A because pressure has no effect on an equilibrium that has equal moles on both sides. But I don't know why the answer is D. Give me sometime, I'll ask my teacher and let you know soon.

As for the tips, especially the one markers. Always answer in context to the question. Try and understand or better, visualize the question. Any one marker following that question would probably sound like : Why was so and so used to blah blah blah? In this case, try and analyse the experiment. This may give you lots of sensible points. Try learning all the diagrams for distillation etc. Good luck!

Exactly !! This should be a very straightforward question, yet the answer is seemingly inexplicable.

I will definitely try thinking of the context first before answering a question,and thanks for the help !!

Reply 11

Sumaiyya1999

4

After the unit 3 paper i have lost all my motivation for this paper as well

Reply 12

Bliss_

Original post by Sumaiyya1999

After the unit 3 paper i have lost all my motivation for this paper as well

i feel ya. i hope the grade boundaries are super low

I hope so

Original post by Sumaiyya1999

I hope so

Don't worry guys, much easier exams had 33/50 for an A.

Reply 15

Sumaiyya1999

4

I am kinda nervous for my overall grade cuz i expected to get a full ums in unit 1 but got a B and that papermwent soo amazing for me i dont know where i went wrong

Reply 16