okay let's try a few quick problems regarding acids and bases the
first one asks the conjugate acid of NH 2 - is and we have some options there
number 2 which compound is not a Lewis acid so which one cannot behave as a
Lewis acid and number 3 an acidic buffer solution can be prepared by mixing
solutions of and then we have four options here so you may want to review
with some of my tutorials regarding acids and bases or buffer solutions and
when you're ready give it a try
so for number one we're looking for the
conjugate acid of NH 2 - in order for this to form its conjugate acid it must
act as a base which means it must gain a proton so NH 2 minus plus h plus is
going to give us NH 3 or ammonia and so ammonia is the conjugate acid of NH 2 -
now looking at number 2 which one is not a Lewis acid so we know that in order
for something to act as a Lewis acid it must be an electron pair acceptor so the
central atom must be able to accommodate another pair of electrons right
something is going to attack it a lone pair of electrons is going to attack
that central atom so what we notice is that these first three bf3 alcl3 and
becl2 all have incomplete octet that means that they can accommodate
more electron density and in fact we've seen things like alcl3 act as lewis acid
catalysts in a number of reactions in organic chemistry so these first three
all can act as a lewis acid however sncl4 that tin atom has a complete octet
it's got four bonds to other atoms so it is going to have a very hard time
accommodating more electron density so that is very
unlikely to be able to act as a lewis acid so option D will be our answer
there now looking at number three we're trying to prepare an acidic buffer
solution now we know that any buffer system is always a weak acid or base and
it's conjugate so it's got to be a weak acid or base so let's look at some of
these options well option C this one's not going to work because we have some
strong electrolytes sulfuric acid is a very very very strong acid that will
dissociate completely and we have sodium sulfate and so number one these are not
even conjugate species right sulfuric acid and sulfate are not conjugates
there's the bisulphate ion is in between them that is the conjugate of either of
those two so that one's just not going to work
option D again we have some strong electrolytes we've got sodium chloride
and we have sodium hydroxide hydroxides a very strong base so hydroxide will
react with water and will have an equilibrium there but that's not gonna
that's not going to give us a buffer solution now looking at option B we have
ammonium chloride and ammonium hydroxide well the ammonium ion looks pretty good
that is a weak acid but we have hydroxide in solution hydroxide is a
very strong base so that is going to give us a basic solution and that's not
gonna work we want an acidic buffer solution so lastly looking at option A
this one is going to work because we've got ammonium acetate and acetic acid and
this will give us an acidic buffer solution because we have acetic acid in
equilibrium with the acetate ion so that will be option A and those are the three
questions regarding acids and bases.