Qualification > Sciences
CHEM AND BIO HELP AND TIPS HERE
rameeziiii:
ok its like this Si + 2F2.... 7.2 grams= 7.2/38...(not 19 as it is the gas molecule not the atom)
so it becomes 0.189.... now since Si needs 2 moles of F2 0.08 moles needs 0.16 moles but F2 has 0.189 and therefore Si is the limiting agent
sarasa:
--- Quote from: Shooting Star on June 05, 2010, 01:37:59 pm ---can anyone pls ans my question... :'(
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Ok calculate da no. of moles of Br2= 25 divided (80*2)= 0.156
then takin da ration Si: Br2 is 1:2 so if silicon is 0.07 then Br2 should be double it that is 0.14
but the real amount is 0.156 which is greater than 0.07 so bromine is in excess nd Silicon is da limiting reagent
Hope I helped
My answer is for da first variant
$H00t!N& $t@r:
--- Quote from: JD46 on June 05, 2010, 01:38:20 pm ---MJ04 Q4 how do i know what salt to use, what cant it be a zinc oxide or hydroxide for preparing an insolubles salt?
I'D LIKE A REPLY! theres been like 3 replies AFTER my post ,but no rresonse to my post! ???
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precipitation method uses two solubles to form an insoluble base
hydroxides are insoluble (except those of ammonia, barium and alkali metal (group 1) cations) so we cant use that
all oxides are also insoluble (except those of calcium, barium and alkali metal cations) so we cant use these either
we have to choose a soluble base. we can use chlorides as they are soluble. therefore zinc chloride+ sodium carbonate= zinc carbonate+ sodium chloride
Im not quite sure of my answer though. can some1 pls confirm
$H00t!N& $t@r:
thnku both for the answer!
i actually got the right answer but i was looking at the markscheme for a different variant! silly me! ;D
anyway Thanks guys!
rameeziiii:
--- Quote from: Shooting Star on June 05, 2010, 01:53:38 pm ---precipitation method uses two solubles to form an insoluble base
hydroxides are insoluble (except those of ammonia, barium and alkali metal (group 1) cations) so we cant use that
all oxides are also insoluble (except those of calcium, barium and alkali metal cations) so we cant use these either
we have to choose a soluble base. we can use chlorides as they are soluble. therefore zinc chloride+ sodium carbonate= zinc carbonate+ sodium chloride
Im not quite sure of my answer though. can some1 pls confirm
--- End quote ---
yeah its correct... although you could use sulphate or nitrate... both are soluble
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