Ultima, for A levels purposes can I simple assume that polar
will always be able to be soluble in polar reagents and non polar
solvents wil mix with non polar reagents ? Ionic salts will always
dissolve because they can form ionic like bonds with polar water
molecules. Anything that can form hydrogen bonds iwith water can
dissolve in water. as long as the bonds holdingh the solid
together is weaker than the bonds that will form with the solvent,
solid will surely dissolve. please correct any misconceptions ! im
struggling with the whole solubility thing ( not the energetics
kind but the bonding of solvent solution )
Not so simple. At O levels, everything is simplistically 'always'.
At Uni levels, nothing is simplistically 'always'. A levels is
between O levels and Uni levels, expect anomalies and having to
examine case-by-case.
'Like dissolves like' is usually applicable for most cases, but
the question can add in more variables to get you to discuss
relative solubilities of a polar solute in 2 or 3 different
solvents, all of which are polar (for example).
Not all ionic salts are soluble, hence you have Qsp and Ksp. But
species like phenylammonium ions and phenoxide ions, are indeed
more soluble than their molecular conjugate acid/base forms, due to
ion - permanent dipole interactions which are stronger than
hydrogen bonds (provided the formal charge is on a small period 2
atom).
Even if a molecule can form hydrogen bonds with water, it may
not be very soluble, because of the non-polar parts of the molecule
(eg. benzene ring) thermodynamically preferring to form van der
Waals forces with the non-polar parts (eg. benzene ring) of the
other solute molecules, while the snobbish water solvent molecules
thermodynamically prefer to form hydrogen bonds with other water
solvent molecules. Hence, aqueous solubility of alcohols decrease
with increasing length of its non-polar hydrocarbon chain.
So once you see it as a beautiful complex spectrum of
solubilities, rather than an oversimplistic black-and-white binary
system of just 'soluble' or 'insoluble', you can let go of your
frustrations and it will finally make logical sense for you.
Also e.g say when an amine is added into HCl, the solution
surely dissolves and forms a salt rite? but isnt it reacting with
the acid which permanently changes its chemical formula and not
dissolving ? compared to maybe amine being dissolved in water which
only forms hydrogen bonds with water and does not react.
Also Hormones must be made up of 2-amino carboxylic acids like
proteins or any kind of amino acid?
Yes, it is reacting with the acid to be protonated, and it's
formula changes from its conjugate base form to its conjugate acid
form, and its conjugate acid form is more soluble than its
conjugate base form, because ion - permanent dipole interactions
are stronger than hydrogen bonding, as long as the formal charge is
on a small period 2 atom.
Hormones may or may not be
protein in nature (H2 Bio students have an advantage over H2
Physics students for this topic). Only proteins are polymers of
alpha-amino acids.