2007 H2 Chemistry
Paper 3 Qn 3 (b)(ii)
My question is what exactly is the information given in Data 1.
Enthalphy change of formation of Ca2+ (aq)= -543 and f- (aq)= -333
??
This data is given together with enthalphy change of atomisation
of Ca(s), enthalphy change affinity of flourine atom and enthalphy
change of formation of CaF2(s).
Do I have to use information from data booklet as well, as it is
not stated in the question ?
2006 H2 Chemistry
Paper 3Qn 5
Write a balance equation when KI(aq) is added to a solution of
Pb2+(aq). A bright yellow precipitate is formed. Further addition
of KI(aq) causes the ppt to redissolve.
My Answer:
2KI(s) + Pb2+(aq) ----PbI2(s)+ 2K+(aq)
Yellow ppt of PbI2 is formed.
PbI2 (s) + I- (aq)----[PbI3]- (aq)
Further addition of KI causes the formation complex ion which is
soluble.
However, the formula of the complex ion given in the TYS was
[PbI4]-. Does that mean my answer is wrong cause I wasn't taught
about this in my school. Is there a way of coming up with the right
complex ions.
Thanks In Advance :)
Qn 1. The data given in the question suffices (for drawing a
Hess Law enthalpy cycle), you do not need any further info from the
Data Booklet. But if any exam qn appears to give inadequate
data, feel free to quote values from Data Booklet to help you
answer the question. It's just that in this instance, further info
is not required.
Qn2. Different JCs teach different content. If you intend to get
a distinction, you cannot rely on just notes provided by any JC
(even so-called top JCs), but must be prepared to peruse multiple
sources. Your fictitious tri-iodo complex ion will not score the
mark. You must give the formula
for the tetra-iodo plumbate(II) ion.
No single source (eg. any single JC's notes) will give an
exhaustive list of complex ions, their formulae, their geometries
and their colours. Cambridge deliberately does not release any
list, to reserve the right to ask on obscure complex ions to test
the candidate's ability to extrapolate and deduce probable
formulae, geometries and colours.
You can find a more complete list of complex ions, their
formulae, their geometries and their colours on Jim Clarke's
website and Rod Beavon's website.