How easy or difficult you find Chem calculations at 'O'
levels, will depend your own background proficiency in mathematics,
and on whether your teacher (whether school or tuition) teaches you
this topic in a way that you can relate to.
Most secondary school students don't really pay attention in
school lessons (partially their own fault, partially the
Singapore school systems' fault), and so struggle to self-learn
this maths-based Chem topic, and unsurprisingly encounter
similar difficulty as that encountered by secondary school
students struggling with mathematics (unlike say, Biology in
which you can still self-memorize without paying much
attention in school, especially for secondary level).
The best way to master 'O' level chem calculations (but this
would work best if you've a tuition teacher to guide you for this,
rather than do-it-yourself) is to practice simple 'A'
level chem calculations that can still be done at 'O'
levels (ie. strictly calculation-type questions that do
not require addition chem concepts or formulae beyond 'O'
levels).
The pedagogical principle being : if you're competent enough to
answer such qns at 'A' levels, you can easily answer such qns at
'O' levels. Of course, this applies more specifically to Chem
calculations.
For the other topics (eg. chemical bonding, energetics, acids
and bases, electrochemistry, organic chemistry, etc), it will be
less profitable (ie. diminishing returns) studying these
at any level higher than at 'O' levels, if you're focused on
preparing to sit for your 'O' levels (as opposed to say, Integrated
Programme learning).
Example of a simple 'A' level Chem calculations qn that can
function as a challenging 'O' level Chem calculations qn :
Solution :
