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  1. K

    Chemistry: Post your doubts here!

    (CH3)3CCH2OH will not dehydrate into an alkene. The reason being is that there can't be a double bond formed, as there are already 3 methyl groups on the carbon on the end. Carbon can only form up to 4 bonds, and so the reaction from alcohol to alkene is not possible here.
  2. K

    Chemistry: Post your doubts here!

    (CH3)3CCH2OH will not dehydrate into an alkene. The reason being is that there can't be a double bond formed, as there are already 3 methyl groups on the carbon on the end. Carbon can only form up to 4 bonds, and so the reaction from alcohol to alkene is not possible here.
  3. K

    Chemistry: Post your doubts here!

    In the question, they give you the initial number of moles of each substance present in the equilibrium. All of them should change by the same amount since the ratios are all 1:1, so lets say the change in the number of moles is x. Therefore, the equilibrium concentrations are (0.70–x) for...
  4. K

    Chemistry: Post your doubts here!

    In the question, they give you the initial number of moles of each substance present in the equilibrium. All of them should change by the same amount since the ratios are all 1:1, so lets say the change in the number of moles is x. Therefore, the equilibrium concentrations are (0.70–x) for...
  5. K

    Chemistry: Post your doubts here!

    The test for unsaturated compounds is with bromine water. Cl2(aq) is yellow, Br2(aq) is reddish brown, and I2(aq) is purple. I'm not too sure about dissolving them in organic solvent, but i suspect they will be the same colour. I couldn't find your question, I think you typed it wrong. P42...
  6. K

    Mathematics: Post your doubts here!

    1. X~B(400, 2/5) But since the number is way too big, and (2/5)(400) > 50, we can use a normal approximation. Mean = np = 2/5 x 400 = 160 Variance = npq = 2/5 x 3/5 x 400 = 96 Therefore, X~N(160,96) You will want to find P(X<165). Note to use continuity correction as you are approximating...
  7. K

    Mathematics: Post your doubts here!

    I'm going to assume you meant 9709 for Math. Anyway, draw out the normal distribution graph, with lines showing - 20(the mean) in the middle - 12 either side of the mean, specified in the question (8 and 32) The area in between, P(8<X<32) is 94%. So far so good? So now you'll want to find...
  8. K

    Re-Sit now or Later

    The scaling in A2 is quite high, so in the end it all depends how high you're aiming for at the end of the year. If you're aiming for C's and B's for your overall A level score, you most likely won't need to resit if you do well ish in A2. Cambridge costs are really expensive, so less resits =...
  9. K

    Chemistry: Post your doubts here!

    ii) 1st order reaction means that the length of half lives are constant. So for "construction lines" just draw lines from y= 0.1 mol/dm3 , y= 0.05 mol/dm3 , y= 0.025 mol/dm3 to the curve, and their respective x values. The length of time between each subsequent half life value should be...
  10. K

    Do i need AS math for engineering? PLEASE HELP

    Like everyone else who replied, I'd say math is a must. First year engineering is generally a general course; without some decent math knowledge, you're pretty much stuffed. If you're going to do engineering, I suggest doing A2 math as well.
  11. K

    Chemistry: Post your doubts here!

    18 ; CaO + SO2 -> CaSO3. You will need to learn it. 20 ; The aldehyde in the second reaction contains a partially positive carbon due to the oxygen bonded to it. The dipole set up makes it vulnerable to nucleophiles (The OH from ethanol). 33 ; Having high activation energy is fairly obvious...
  12. K

    Physics: Post your doubts here!

    It will stop vertically polarized light.
  13. K

    Doing AS Level Chemistry?

    Its not necessary for you to take IGCSE chemistry before going for AS, but its strongly recommended, since AS builds up on IGCSE as a foundation. ie. Organic chemistry knowledge about alkenes, alkanes etc are taught in IGCSE, and are carried on further in AS. Basic moles calculations are taught...
  14. K

    kinematics (projectile)

    Well, generally for projectiles, they'll give you a question where they will give you an angle, and an initial velocity. The very first thing you'll have to do is to find the horizontal and vertical components using SOH CAH TOA. Vertical: u sin theta Horizontal: u cos theta Where "u" is the...
  15. K

    Physics, Chemistry and Biology: Post your doubts here!

    There is no 0590 in IGCSE. I think you are referring to O levels 5090, which is sat in SE asia. Now, I can't find the marking scheme but it seems that you're not the only one. http://www.xtremepapers.com/community/threads/5090-1-may-june-2002-biology.4712/ All his answers seem to be right...
  16. K

    Physics p5

    Absolute uncertainty is pretty much just the smallest significant figure for your recorded results, or the lowest scale on your instrument of measurement. I can't find the June 2011 paper but i'll give you some examples. eg. - you have a result of 209.3g. absolute uncertainty is (+- 0.1g) -...
  17. K

    Biology; Chemistry; Physics: Post your doubts here!

    Cu reacts with water, but this reaction is VERY slow due to its relatively unreactive nature. Copper left in moist air will form CuCO3 and Cu(OH)2 in a roughly 1:1 proportion.. 2 Cu (s) + H2O (g) + CO2 (g) + O2 (g) → Cu(OH)2 (s) + CuCO3 (s)
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