1. Some data is given below (i only extract the relevant
parts)
Substance type of
bonding
mp/deg
cel
bp/deg cel
Iodine
covalent
114 184
In the question, i was asked to name the substances that are NOT
solids at r.t.p.
From the table, we know iodine IS a solid at r.t.p since it
melts at 114deg cel. so i did not name iodine as not being a solid.
But the answer did include iodine. Quite a controversial question
since the iodine we use in the lab is a liquid.
2. May I know what are the conditions for esterification?
Is it H2SO4 as catalyst, 200 deg cel temperature and 1000 atm?
(I might have mixed up the parts on temperature and pressure.
Please correct.) As far as I know, the TB only tells us to use
H2SO4. I did this question in my prelims but all the corrections
are with my teacher so i can't check up the answer.However the
answer in a similar question from TYS gives the conditions as
contrn H2SO4 as catalyst and heat under reflux. For O level, which
is the accepted answer?
3. Regarding the fractional distillation of crude oil, do we
needa memorise the number of C atoms and boiling range of each
fraction? (If I am not wrong, my teacher said there's no need to
memorize. But I want to confirm this)
4.Here are 2 equations of the combustion of octane and hexdecane
respectively
2C8H18 + 25O2 ->
16CO2 + 18H2O
2C16H34 + 49O2 -> 32CO2 +
34H2O
Using the equations, explain why hexdecane burns with a smokier
flame than octane.
The model answer is: 1 mol of octane required only 12.5 mols of
O2 for complete burning whereas 1 mol of hexadecane required 24.5
mol of O2 for complete combustion. Therefore, when hexadecane
burns, more C is left unburnt making the flame smoky.
For me, I compared usin ghte no. of moles of CO2 produced. But
after taking a look at the answer, I feel that my answer didn't
really answer the question because indeed, if we have more C atoms
left, it means that combustion is not as complete, hence more smoky
reaction.
5. Solutions of 2 salts, A and
B, were electrolysed using Carbon eletrodes. The
following products were collected
Salt
Products
A
O2 and H2
B Cl2
and H2
Suggest the names of the 2 salts
I wrote the answer as aq. NaCl and concentrated NaCl for A
and B respectively. But for the answer given, they list A as sodium
sulfate. Are the namings strictly restricted to TWO DIFFERENT
salts?
Thanks
1) The I2 can sublime at room temperature into I2 vapour
4) Unburnt C is what causes the smoke to be black. CO2 is
colourless and thus does not affect the colour of the smoke
regardless the amount.