Debrief -> Science Chemistry MCQ

• Darkness_hacker99

  6 Nov 07, 02:54

  Discuss here
• University Of Cambridge

  7 Nov 07, 13:02

  
  
  
  
  
  
  
  
  
• University Of Cambridge

  7 Nov 07, 13:08

  
  
  
• kenshin_himura

  7 Nov 07, 13:31

  opps i rmb now
• Darkness_hacker99

  7 Nov 07, 17:38

  My suggested answer:
  
  Q21) D
  Q22) C
  Q23) D
  Q24) C
  Q25) A
  Q26) B
  
  Out of the 20 chemistry question, the question I like most will be this. On the surface it looked simple, but it's testing Limiting reactant, and calculation of excess reactant.
  
  First step is to determine the molecular formula. After you've done with your calculation, you'll get FeS.
  
  Then next is to find out which is the the limiting reactant. After the calculation, you'll know that Fe is the limiting reactant, and of course S is in excess.
  
  No. of mol of FeS/ No. of mol of Fe = 1/1 = 1
  
  No. of mol of FeS = 1 x 0.125 = 0.125 mol
  
  Mass of FeS = 0.125 x (56 + 32) = 11g
  
  Final step is to fine out the mass of excess reactant(S).
  
  As calculated earlier(not shown here), take the no. of mole of S minus the no. of moles of Fe. Which is 0.219 - 0.125 = 0.094 moles of S in excess
  
  Then 0.094 x 32(Ar of S) = 3.
  
  Answer: B
  
  Q27) D
  Q28 ) B
  Q29) D
  Q30) C
  Q31) A
  Q32) D
  Q33) A
  Q34) C
  Q35) C
  Q36) C
  Q37) A
  Q38 ) B
  Q39) A
  Q40) B
  
  Edited for Q34, thanks kester for pointing out my mistake.
• ceecookie

  7 Nov 07, 17:42

  Oh,i dont wanna check my ans.Scared of finding out how bad i done
• lpx88

  7 Nov 07, 17:43

  Chemistry ah..i see i sian ah Next monday i die liao
• Y_Shun

  7 Nov 07, 18:23

  that person who posted the question papaer got alot wrong leh.
• University Of Cambridge

  7 Nov 07, 19:58

  Originally posted by Y_Shun:

  that person who posted the question papaer got alot wrong leh.

  This O Level Paper belongs to another person.
• lolhahalol

  8 Nov 07, 09:10

  although i dont take this paper
  but the FeS question
  I think that first u get 7+7 = 14g
  14g - 11g = 3g
  3g is the mass of sulphur
  Iron is limiting so nothing left
  so answer is 11g Fes 0 Fe 3g S
• kester

  8 Nov 07, 13:21

  Assuming Darkness_hacker99 answers are correct, which I'l ltrust him on this one.
  
  Chemistry MCQ : 18/20.
  
  Not too bad actually.
  
  Fermentation doesn't involve water. How silly of me =.="
  
  Regarding Q34, Doesn't both sulphur dioxide and nitrogen oxide affect limestone ?
  
  My ans is C.
• Darkness_hacker99

  8 Nov 07, 14:25

  Originally posted by kester:

  Regarding Q34, Doesn't both sulphur dioxide and nitrogen oxide affect limestone ?
  
  My ans is C.

  You are right.
  
  Both SO2 and NOx does plays a part in Acid rain. I admit my mistake.
  
  Thanks for pointing out
• PwnYou

  8 Nov 07, 19:33

  may i ask
  
  why is qns 24 C?
  why is qns 40 B?
  
  oh, i tink i got 3 wrong.
• Darkness_hacker99

  9 Nov 07, 05:39

  Originally posted by PwnYou:

  may i ask
  
  why is qns 24 C?
  why is qns 40 B?
  
  oh, i tink i got 3 wrong.

  
  
  The answer is C.
  
  The ions in ionic compound are arranged in a lattice form, that why it's called ionic lattice.
  
  Property of Ionic compound:
  1) When molten, it conducts electricity due to moving electrons.
  
  2) have high melting points.
  
  
  
  The answer is B.
  
  The word 'poly' means many. Comparing the linkage which I have posted(below), there is a different between 'Amide' and 'Ester' Linkage.
  
  If you look can see... Polyester seems to be the most similar out of the other options.