some salts are soluble in water whereas
some are insoluble in a previous lesson
we learned how to make and isolate
soluble salts in this lesson we will
learn how to make and isolate insoluble
salts
let's say you have been given two
solutions sodium iodide and silver
nitrate these two salts are soluble in
water so aqueous solutions are formed
add silver nitrate dropwise to sodium
iodide and you will notice that a bright
yellow solid is formed
this bright yellow solid is known as a
precipitate which is an insoluble solid
formed from combining two solutions
this is known as the precipitation
method
sodium iodide and silver nitrate have
undergone a double displacement reaction
whereby the sodium ion and the silver
ion have switched places creating silver
iodide and sodium nitrate
since sodium iodide and silver nitrate
are soluble in water they form aqueous
solutions in the reaction equation we
represent this using aq
in brackets as a subscript right after
its formula
here is a big question we know that
sodium nitrate and silver iodide are
formed but how do we know which is the
precipitate
to do so we must refer to the solubility
table as we have learned in a previous
lesson you may know the solubility rules
off by heart
all nitrate salts are soluble in water
all iodide salts are soluble in water
except when combined with lead and
silver
therefore silver iodide is insoluble in
water and is that bright yellow
precipitate formed in this reaction
referring back to the equation we
represent this by writing aq in brackets
as a subscript after sodium nitrate and
s in brackets as a subscript after
silver iodide
to isolate the silver iodide precipitate
we filter it through a funnel lined with
filter paper since it is insoluble in
water we can rinse the contents of the
beaker with distilled water to ensure
that we get all of the precipitate
produced
distilled water is simply water with
most ion impurities removed this
filtration process
separates a solid from a liquid
the solid collected is known as the
residue and the liquid that the solid is
separated from is known as the filtrate
are you ready for a challenge
let's grab a pencil and a piece of paper
predict the products for the double
displacement reaction of barium chloride
and potassium sulfate and write the
reaction equation remember to include
the state symbols and to fully balance
the equation
the answer is
did you remember to balance the equation
and did you get the correct answer using
the solubility table we can see that
almost all chloride salts are soluble in
water so potassium chloride in water
forms an aqueous solution
almost all sulfate salts are soluble
except for a few with one of them being
the barium sulfate precipitate so the
reaction equation including all the
state symbols is
this barium sulfate precipitate is in
fact so insoluble that one can ingest
this and have it safely pass through our
gastrointestinal tract without being
absorbed by our bodies it is used as a
contrast agent to image our
gastrointestinal tract using x-rays this
is not the only method to form an
insoluble salt another method is by the
direct combination of the constituent
elements insoluble salts can be formed
using two methods
via precipitation or by the direct
combination
you