IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE O - Level => Sciences => Topic started by: nox_fjmoony on May 31, 2009, 07:10:45 am
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questions: 4, 6, 10,1 1, 17, 21, 24, 26, 32, 36.
Also it would be great if you could explain how to arrived at the answers, and the difference between the effect on the equilibrium and the effect on the rate of reaction.
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read these tips first:http://www.cambridgestudents.org.uk/subjectpages/chemistry/OLevel/Examiner_Tips_for_O_Level_Chemistry_5070_FINAL.pdf
4. i'm confused on this one too...it is calcium...ohhhh i get it!!! calcium is insoluble in excess NaOH...u see,since it was added too quickly, Al and Zn dissolved in excess...ammonium is not possible since it gives off a gas no matter what
6. changes in state involve the change in spacing BETWEEN molecules...remember that always.
7. r.f is dist travelled by solute/distance by solvent FROM THE POINT WHERE THE MIXTURE TO BE SEPARATED WAS PUT.
10. lead sulphate is insoluble....to make insoluble salts, u need soluble + soluble = insoluble + soluble ..answer is C ... D is not suitable because water is also formed...we need a soluble product,not just water
11. it is D.this is because XCl3 shows oxidation state of X is +3...look for the choice in which there's 3 of the other atoms.
17. increase in pressure would not help because there's 2 volumes of gases on both sides...the reaction is exothermic,so a decrease in temp. is most suitable...increase in temp. would cause decomposition,an endothermic process,of hydrogen iodide
21. it is a reducing agent...the test for oxidising agent is to react it with a reducing agent...the colour changes show that potassium dichromate and manganate have been reduced,by a REDUCING AGENT,the gas,i.e....
24. D...these are the characteristics of acids....what the examiner is asking is which statements show some chem/phy properties of acids.
26. remeber, sodium sulphate has the formula Na2SO4,so Se will also give Na2SeO4
32. P can be any of the MAZIT metals,which leads us to C or D. zinc needs carbon for reduction,whereas hydrogen is created...so,D is the answer
36. remember this-if a carbon is attached after the oxygen with the = double bond,then that one is the acid,with the single on,it is the alcohol...so,OCH3 is the alcohol part...one carbon means methanol...the other part has 3 carbons,so it is propanoic acid...
there u go..hope i'm not too late as i was tooo busy today...i tend to leave everything for the last day :P
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me too. I haven't started revising physics yet. But Inshallah I will, after a bath and lunch lol. Thanks man.
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yeah...physics is way tooooo lengthy...everytime i think i'm done another topic comes out of nowhere...i hope the papers are easy... :-[...anyways,can u plz explain the purpose of split ring in motor and slip rings in generator?
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in the motor...a commutator is used..
it always keeps the current flowing in one direction...
when the commutator is at 180 degree,,no current is flowing , however due to its momentum, the commutator turns ...
the current continues to flow ..and the commutator turns..
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commutator......reverses da direction of da current every half a rotation to keep da coil turning in da same direction.......
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http://www.walter-fendt.de/ph11e/electricmotor.htm
http://www.walter-fendt.de/ph11e/generator_e.htm
this will help you understand better