Garrick_3658 had sent me a msg. In a nutshell, he said :
[Quote] Is it possible for you to provide me with a simplified
step-by-step answers for these questions that you posted? Well,
even my school teachers are dumbfounded by these things. They even
questioned its standard, whether is it of O Level
calibre. [/Quote]
In a nutshell, I replied :
[Quote] These questions are do-able at both 'O' levels and 'A'
levels, meaning while the difficulty or
complexity standard is fairly high, there is no
new concept or new mathematical formula that you need to learn
beyond the 'O' level syllabus, in order to complete these
questions.
And I give these questions to (and coach) my tuition
students, both 'O' levels and 'A' levels. Indeed, some of my ('O'
level) students remarked that some of their own teachers in school
may have difficulty solving these questions. But they (my 'O' level
students) could appreciate how attempting and eventually solving
(albeit more often than not with my guidance and teaching) these
questions, benefited them in terms of depth
and scope of thought.
So to answer you, are these questions 'O' level standard? Yes
and no. No, in that these are probably somewhat more challenging
than most 'O' level questions you would come across in the exam.
Yes, in that there is nothing new you need to learn (eg. 'A' level
stuff), in order to solve these questions... other than
challenging yourself to think a little deeper and see a little
further, to see the forest for the trees, so to speak.
So, now that this is out of the way, it's up to you whether you
think it worth your time to solve these questions, or perhaps
(depending on the individual student) it might be wiser to spend
your time on 'O' level TYS questions instead.
Perhaps I'd leave you with this recommendation : if your mastery
of the basic foundation, ie. stuff the syllabus
indicates you need to memorize, definitions, drawings, methods,
etc; is not there yet, then you'd be better off cheonging the 'O'
level TYS.
But if you find the TYS questions too easy for you and fancy a
challenge (that is beyond the typical 'O' level standard, but still
do-able at 'O' levels), then attempt my questions.
Finally, if you wish to attempt these questions, eg. the 2
questions you mentioned, and you would like my help, then
make a new post on the forum, and we can discuss these
questions. I won't type or post or send you the complete worked
solution though, instead what I'd do, is comment, guide and
hint, as you attempt these questions. So in the new posts that
you'll be making shortly (assuming you're still interested in
attempting these questions), share your thought process and
attempted working along the lines of, "I've done these calculations
so far, and have made these assumptions, and plan to solve it this
way... are there any conceptual errors I made? Would it be correct
for me to say that..." and so on.
1 Week to 'O' Levels. Make good. 
[/Quote]
So here are the 2 questions of interest to Garrick_3658.
3) A mixture of
MgSO4.7H2O and
CuSO4.5H2O is heated until a mixture of the
anhydrous salts, is obtained. If 5.0g of the hydrated mixture when
heated gives 3.0g of the anhydrous salts, calculate the % by mass
of CuSO4.5H2O in the initial hydrated
mixture.
4)
When Fe and
Fe3+ are mixed together, a reaction occurs in which
Fe2+ is produced. What is the ratio of Fe to
Fe3+ required to produce equal moles of Fe2+
and Fe3+ when the reaction is
complete?
I'd now invite Garrick_3658 and any other interested*
'O' level students ('A' level students are also welcome) to
attempt these questions here in this thread and to share your
working here, or feel free to ask questions to confirm, verify, or
clarify your concepts relevant to these questions.
*Note : As I msg'd Garrick_3658, if you're an 'O' level student
who hasn't already memorized and mastered your basic foundations,
then you're better off cheonging the 'O' level TYS instead of
attempting these questions. Don't waste your time if you know
you're not yet ready, you have 1 week left to your exams, make
good!!!
Now, to kickstart this thread, here are a couple of hints for
the 2 qns.
Q3 Hint : Let x and y be the no. of moles of the hydrated (or
anyhydrous, up to you, no difference to no. of moles)
copper(II) sulfate and magnesium sulfate, respectively. Next, based
on the information provided by the question, write two equations in
x and y, and solve simultaneously.
Q4 Hint : First, write the relevant half equations to obtain the
balanced RedOx equation. Next, although not strictly required (ie.
it's optional), it may help you to get a mental handle on the
situation if you write out an ICF table - Initial (no. of
moles), Change (in no. of moles), Final (no. of moles).
The Game's Afoot!
