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  1. Metanoia

    Chemistry: Post your doubts here!

    2X(NO3)2 --> 2XO + 4NO2 + O2 let x be the Mr of element X moles of X(NO3)2 = 3/(x+124) mass of XO = 3 - 1.53 = 1.47 g moles of XO = 1.47/ (x + 16) Based on the balanced equation, moles of X(NO3)2 =moles of XO Therefore, 3/(x+124) = 1.47/ (x + 16) Solve for x.
  2. Metanoia

    Chemistry: Post your doubts here!

    For the question, its actually 1200 million tonnes (the total mass of limestone).
  3. Metanoia

    Chemistry: Post your doubts here!

    When you say equilibrium shifts to the left, which equilibrium equation are you referring to? And how do you conclude it would shift to the left? For weak acid, [H+] = square root (Ka*[acid]) The concentration of Fe2(SO4)3 is o.1 mol/dm3. But since we are using concentration of Fe3+ , we do...
  4. Metanoia

    Chemistry: Post your doubts here!

    Qn 24, upon dehydration, we have either 2-methylbut-2-ene or 3-methylbut-1-ene Neither versions have cis-trans isomerism, so there are only a total of 2 possible alkenes.
  5. Metanoia

    Chemistry: Post your doubts here!

    If reaction 1 is slowest Rate determining step is based on reaction 1: H2O2 + I- --> IO- + H2O The powers of the rate equation is based on the stoichiometric ratio of the reactants , so its [H2O2]^1 and [I-]^1 If reaction 2 is slowest, we combine reaction 2 with the reactions that occur before...
  6. Metanoia

    Chemistry: Post your doubts here!

    A pretty interesting analysis. I would say a peptide bond is when the N-terminus forms a bond with the C-terminus of the amino acid (the N-terminus and C-terminus should be both connected to the same carbon). The side chain of (CH2)4 NH2 is not considered the N-terminus. fii) Imagine...
  7. Metanoia

    Chemistry: Post your doubts here!

    1) 4 bond pairs, 0 lone pairs. Tetrahedral 2) 3 bond pairs, 0 lone pairs. Trigonal planar 3) 2 bond pairs, 0 lone pairs. Bent.
  8. Metanoia

    Chemistry: Post your doubts here!

    This takes a bit of visualization. Imagine viewing the molecule from the side, the blue parts are the 3 front groups, the red parts are the 3 back group. Fix your front COOH at 12 o'clock position, fix your back COOH at 6o'clock position. Change the positions of H and OH groups to get unique...
  9. Metanoia

    Chemistry: Post your doubts here!

    How do we know which line denotes what atom? The useful background knowledge required is that chlorine has two main isotopes; Cl- 35 and Cl-37. So, from left to right, we have Cl-35 , HCl (where the Cl is Cl-35), Cl-37 and HCl (where the Cl is Cl-37). Even if we do not have that background...
  10. Metanoia

    Chemistry: Post your doubts here!

    Ag+ + e- --> Ag E = + 0.800 V Shifting the eqm to the right will increase the E value, shifting to the left will decrease the E value. Since you correctly said the eqm would "shift to LHS", you can see that the E value should decrease.
  11. Metanoia

    Chemistry: Post your doubts here!

    I believed you have gone through the ms already which I am posting below. Which part of the answers do you need to clarify? Q1 Q2 Q5 Q7 As for patterns in setting of questions, I don't really look at it. I seldom encourage "spotting of questions".
  12. Metanoia

    Chemistry: Post your doubts here!

    Cis-trans and EZ are both geometrical isomers but are not the same. Cis-trans is more specific, it requires at least 2 out of the 4 groups (at the C=C) to be identical to each other. ClCH=CHCl or ClCH=CHBr EZ is more general, it can consist of 4 different groups. ClCH3C=CHBr
  13. Metanoia

    Chemistry: Post your doubts here!

    There is EZ isomerism at the C=C double bonds.
  14. Metanoia

    Chemistry: Post your doubts here!

    With so little time left, it makes more sense to focus on the main and common concepts rather than a list of "unexpected questions". Such a "list" will never be accurate nor exhaustive; and would only add unnecessary stress instead.
  15. Metanoia

    Chemistry: Post your doubts here!

    Short answer: 1.67V is for neutral/mildly alkaline conditions 1.52V is for acidic conditions. In case you are wondering, the 0.56V half equation is not commonly needed as the MnO42- is unstable and tends to undergo disproportionation.
  16. Metanoia

    Chemistry: Post your doubts here!

    Let concentration of eqm concentration of Pb2+ be x [Cl-] = 2x Ksp = [Pb2+][Cl-]^2 = (x) (2x)^2 = (x)(4x^2) = 4x^3
  17. Metanoia

    Chemistry: Post your doubts here!

    Its not easy to say what is important or not. Its best for you to look through the objectives listed for the respective chapters and make sure you understand the requirements. http://www.cie.org.uk/images/128593-2015-syllabus.pdf If any objective seems unfamiliar, its an indication you need...
  18. Metanoia

    Can somebody guide me through CIE A-Level Past Years Codes?

    S15_ms_11 means 2015 summer (june) _ marking scheme_paper 1 (variant 1) S15_qp_11 means 2015 summer (june) _ question paper_ paper 1 (variant 1)
  19. Metanoia

    New chemistry website http://metatutorchemistry.blogspot.sg/

    New chemistry website http://metatutorchemistry.blogspot.sg/
  20. Metanoia

    Chemistry: Post your doubts here!

    C2H4O --> C3H6O3 moles of ethanal used = 4.4/44 = 0.1 mol moles of lactic acid expected = 0.1 mol mass of lactic acid expected = 0.1 x 90 = 9 g % yield of lactic acid = actual mass/expected mass x 100% = 5.4/9 x 100% = 60%
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