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  1. X

    Chemistry MCQ thread...

    i dunno for sure because nothing like this came up before. but i'll put a yes for my own answer cause when you draw out the mechanism, you include the intermediate stage too rite?
  2. X

    Chemistry MCQ thread...

    both Sn1 and Sn2 have intermediates its just that the Sn2's intermediate is a very fast step such that it is often ignored.
  3. X

    Chemistry MCQ thread...

    ans is D. Sn1 is undergone by tertiary haloalkane Sn2 is undergone by primary and secondary haloalkanes - Sn1 and Sn2 are reaction mechanism - when tertiary undergo substitution, the halogen has to break off first before the new nucleophile can fit in - so it's like one by one, break then...
  4. X

    Chemistry MCQ thread...

    isin't the answer A? cause from what i know, chlorine is a stronger oxidising agent than sulphuric acid.
  5. X

    Chemistry MCQ thread...

    24. ans : A. - the alcohol will be dehydrated to form an alkene. - the double can be on the left or right, making it 2 types. - if the double bond is on the left side, then the alkene have cis-trans isomers in total : 3 34. only 1 rite?
  6. X

    Chemistry MCQ thread...

    1 and 2. when propane form free radicals that DOES NOT contain any halogen group, there are only 2 types of free-radical. either its CH3CH'CH3 or CH3CH2CH2' and if you join them together, the one in 3 is not possible because no matter how you separate it into two, one of them is bound to have...
  7. X

    Chemistry MCQ thread...

    what do you not understand? A - cannot because there are no changes in the oxidation number B - for AS level, electrophilic addition occurs only across C=C D - from alcohol to aldehyde is oxidation ans : C because reactions that occurs across C=O is nucleophilic reaction. *the mechanism is...
  8. X

    Chemistry MCQ thread...

    according to what my lecturer found, CO has a very very very long half-life and cannot be oxidise easily. thats why.
  9. X

    Chemistry MCQ thread...

    pure water has no concentration?
  10. X

    Chemistry MCQ thread...

    num. of mole of CS2 = 10/24000 = 4.17 x 10^-4 mole number of mole of oxygen needed = 3 x 4.17 x 10^-4 = 1.25 x 10^-3 mole vol of oxygen needed = 1.25 x 10^-3 x 24000 = 30cm3 - so we have 20cm3 of unreacted oxygen volume of CO2 produced = 10cm3 volume of SO2 produced = 20Cm3 - so volume of gas...
  11. X

    Chemistry MCQ thread...

    nope, PH3 is 104 not 107. NH3 is 107. although both have trigonal pyramidal shape the main reason for the difference is - N is more electronegative than P - bonding electrons are closer to N than in P - the electrons are closer hence the bonds in N experiences a greater repulsion than in P
  12. X

    Chemistry MCQ thread...

    formation 1/2H2 + 1/2I2 -> HI bond energy = broken - formed = ( 218 + 75.5) - ( 299) = -5.5 EXOTHERMIC!!!
  13. X

    Chemistry MCQ thread...

    D * shouldn't the answer for this be A? i though the cation is the same throughout the group? H+ right?
  14. X

    Chemistry MCQ thread...

    Ans : A - the percentage of N is the fertiliser is 15/100 = 0.15% - in 14g of fertiliser, the amount of N is 14 x 0.15 = 2.1g - the number of moles of N is 2.1g of N is 2.1/14 = 0.15 mole - concentration = mole/volume, hence, 0.15/5 = 0.03moldm-3 right?
  15. X

    Chemistry MCQ thread...

    oh well, if u ask me, my teacher said 1st, balance elements that only occur once on both side of the equation. - so from the above eqn, that special element is N and S. then after that you go to elements that are used more than once. - from our eqn, the elements are O and H.
  16. X

    Chemistry MCQ thread...

    and please help me with oct nov 04 no 10 11 12 and 21.. i cant paste it here because there are pictures and tables.. I have the same query regarding 19. Please can someone tell me how to solve it???? Pleease :o O/N 04 Q 10 - partial pressure of gas1 = (num.of mole of gas1)/(num. of mole...
  17. X

    Chemistry MCQ thread...

    question 19 just write out the equation and balance. quite easy (NH4)2SO4 + 4O2 -> H2SO4 + 2HNO3 + 2H2O
  18. X

    Chemistry MCQ thread...

    you actually typed the question wrongly, it's suppose to be ethane. well talk about ethane before we go to ethene. so ethane + bromine = free- radical substituition. its actually very very long to type and the answer is 9. * u should check your book under free-radical substituition, I M 100%...
  19. X

    Chemistry MCQ thread...

    optical isomers - always look for C=C or anything with double bond, and eliminate them - when given a long chain, you'll just have to check all the C atoms one by one - if both sides of the C are not symmetrical, then they are considered different groups ( look at the pic for reference ) * well...
  20. X

    PHYSICS MCQ thread

    using the normal example with two parallel plates connected across a voltage. Electric field strength = V / d and the F = Eq *q being the charge of the charge itself so back the question, Q is like the two parallel plates Q provide the E but when it comes to the F, we use the charge of q not Q.
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