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  1. D

    Chemistry: Post your doubts here!

    For 27 The acid will cleave the ester group removing the -OCH3 group. Structural formulas like this can be confusing. I would suggest filling in the carbon atoms so that you can clearly see that this is an ester. The treatment with hydrogen will then reduce all the double bonds so the answer...
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    Chemistry: Post your doubts here!

    The slowest step in the reaction is the rate determining step and therefore only the species involved in that step will determine the overall rate. If step 1 is slowest then the rate will only depend on the concentrations of H2O2 and I-. Since it is a bimolecular reaction the order will be...
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    help grades calculation

    I divided by two because I couldn´t think of anything else to do with the difference between the two grades. However these calculations are not relevant because for the first time they give the thresholds for A* with the June grades. My number does not agree with theirs. Happily the threshold...
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    Physics: Post your doubts here!

    The weight of the helicopter must equal the downward force of the blades on air. So we need to calculate the force of the blades on air. We cannot use F = ma because we do not have acceleration and cannot calculate it from the information given in the problem. So we use instead F=rate of change...
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    So You Think You Know Probability?

    Have you considered doing M1 instead of S1? Probability is weird. Some people can do it and some can not. It is like those that cannot do not have the wiring in their brains that is necessary for them to easily picture and solve the problems. For me there is no comparison between doing M1 and...
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    Physics: Post your doubts here!

    15) Two ways to look at problem. The top half of the water on the left fell to the other side. The essence of solving this problem is to remember that the position and motion of any mass can be reduced to that of its centre of gravity. The centre of gravity of the top half of the water is...
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    Chemistry: Post your doubts here!

    Ionisation energies are a measure of the energy of an electron in an atom and these energies can be compared to the electron configurations of the atoms. In group I the amount of energy needed to remove the 2nd electron is much greater than that needed to remove the 1st electron. This is because...
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    Physics: Post your doubts here!

    Q 10 From the syllabus you are supposed to know that Newt´s second law is that the force on an object is the rate of change of momentum. When asked to define force this is the definition that you are supposed to give and not F = mass x acceleration. So the average force = average change of...
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    a little help in physics??

    I have some difficulties pasting my comments on your questions. Take the question from 12 may/june 2011 Q6. The first question your mind should ask is, “where is this question from in the syllabus?” The exact place is “describe and explain motion due to a uniform velocity in one direction...
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    a little help in physics??

    Well, if you love physics then you should be able to make friends with it (him? she?) and have a very constructive relationship. You should enjoy the subject. First do not allow yourself to fall into a state of panic. The only time in life you are allowed to do that is when you are in a plane...
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    Chemistry: Post your doubts here!

    ok, the structure did not show up correctly when I pasted it.
  12. D

    Chemistry: Post your doubts here!

    For 22 choice A is not correct because you could get substitution at both 1 and 2 positions. For B and D the two are dilute aqueous solutions which are not going to do much of anything. This leaves C which is the reaction of an alcohol with SOCl2 which is the preferred method for making alkyl...
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    a little help in physics??

    Ok, I was fooled by this one too. You have to remember that the total velocity is the area under the graph since a =dv/dt so dv = a dt then if you integrate both sides you get the velocity. If you imagine adding up the area under the acceleration graph it first increases at in increasing rate...
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    Chemistry: Post your doubts here!

    Sorry, I myself got confused with question 27. I looked at it for 5 minutes and did not read it correctly. Since the question is about alkenes I was thinking about electrophilic addition and I read choice A as electrophilic addition. Possibly because right below it is the word addition...
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    a little help in physics??

    It can not be zero because some of the water is at a lower level than at the start. How to calculate the loss? At first it seems very difficult because each layer of water initially has a different amount of potential energy. Then one remembers that the problem can be simplified by the use of...
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    Chemistry: Post your doubts here!

    Actually I reread the question and here again is why MCQ is difficult and you have to read the questions like a lawyer reading a contract. When I read choice A I was thinking electrophilic addition reaction because that is what alkenes do. However the choice is electrophilic substitution which...
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    Chemistry: Post your doubts here!

    27) It took me a while to come to the answer of C. There is no denying that if the two molecules are hydrolysed that the products will be the same. However alkenes are normally said to undergo electrophilic addition. So what is wrong with A? The addition of bromine occurs in two steps. The...
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    Engineering admission help pleaseeeee!!!!!!!

    Well since no one has offered a comment I will give you what I know. I have known students to enter Canadian universities with A levels. However you should have long ago checked the entrance requirements for the universities to which you wish to apply to make sure that you have met them. If...
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    Chemistry: Post your doubts here!

    1/10 of the vanadium ions were used so this is .0013 moles Vn where n is the oxidation number of the vanadium in the complex. .0208 X .025 = number of moles KMn O4 that reacted this is equal to .00052 moles Mn goes from the +7 to the +2 state in the reaction and so each ion gains 5...
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    Physics: Post your doubts here!

    The starting momentum of ball A at right angles to its motion is zero. (The y-component is zero). Therefore after the collision y-components of the momentum of the two balls must be zero. Since the y-component of the momentum of ball A after the collision is 2.6*1.2*sin(30) then the momentum of...
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