hey these are the missing answers to the prelim paper (chemistry)..(after my session with lkp)
Either 5b) need to know that Mg + NH3 ---> Mg(x)N(y) + hydrogen
Mg(x)N(y) + water -----> Mg(OH)2 + NH3
u balance then u will realise that x=3 and y=2.. (coefficient of water is 6)
the figures are just there for u to check your final answers..
5di) Ksp of BaCO3 is lower than that of CaCO3..
if small quantities of CO2 were to be detected..
BaCO3 is preferred becos the [ carbonate ion] might be high enough such that the I.P of BaCO3 is higher than Ksp of BaCO3 but low enough such that I.P of CaCO3 is smaller than Ksp(CaCO3)..
dii) one disadvantage of using Ba(OH)2 is becos its such a reactive base such that it will be able to react with CO2 in the air...
5 or) i) to blow out the bromine gas into the vats
ii) bromate(V) is produced becos Br2 react with OH- ions in the sea to form bromide ions..bromate(v).. and water..( the 3-6-5-1-3 equation)
5c) the ans is ICl3..( 1.83g refers to AgCl)
find no of moles of Cl-
find no of moles of Iodine that reacted with s2o3..(brown solution is iodine solution)
compare mole ratio..should be 3/2the equation: IxCly + I- ---> iodine + Cl-
then balance!
ok gd luck for prelims.. and btw if u haven realised..polymers and monomers out of syllabus...so no need mug that much after all..(i hope everyone stops mugging to visit the class blog for a while!!)HAHAHAHA
okay. the above was the courtesy of qingsheng so if you still have any questions i think you can ask him.
if you want the original email he sent to me, you can ask me! (: ok. happy mugging!