when we talk about a salt we don't just
mean regular table salt we are actually
referring to a very wide spectrum of
ionic compounds or compounds made of
negative and positive ions
some of these salts like table salt
which is sodium chloride are soluble in
water
some others such as barium sulfate used
as a contrast agent when forming an
x-ray image of the gastrointestinal
tract are insoluble in water
in this lesson we will learn two
different methods to form and isolate
soluble salts
you have likely encountered copper ii
sulfate either as crystals or in
solution but have you ever wondered how
it is made
did you know that you can make your very
own copper ii sulfate crystals
add two scoopfuls of copper two oxide
which is a black powder into a beaker
then add sulfuric acid so that all of
the copper 2 oxide powder is covered and
a bit more
mix with a glass rod not very exciting
is it but if you heat this over a
roaring bunsen burner flame while
stirring it turns bright blue
this is how you know that the reaction
is complete let's remove it from the
heat and let cool while we discuss the
chemistry of this reaction
copper ii oxide reacted with sulfuric
acid to give copper ii sulfate and water
as copper ii sulfate is soluble in water
a solution is formed
copper ii oxide is a metal oxide which
is an insoluble base and as you may
already know sulfuric acid is an acid so
what has happened here is an acid-based
neutralization reaction where a salt and
water has been formed an acid-base
neutralization reaction is a type of a
double displacement reaction
the copper and hydrogen ions have
switched much like how certain dancing
partners can switch
therefore a soluble salt can be made by
reacting an insoluble base with an acid
referring back to your solution you may
find some unreacted copper ii oxide
powder that can be removed by filtration
here is a mini challenge how can we
remove water without removing copper ii
sulfate please pause to think about this
and resume when ready
we can evaporate some water right over
the bunsen burner flame
then we can place the solution in a
crystallizing dish near a windowsill and
find that copper ii sulfate crystals
have formed
these crystals are bright blue and you
may notice that they have an irregular
rhombus shape
we can also make soluble salts by
reacting a soluble base or an alkali
with an acid we will make sodium
chloride
by titrating hydrochloric acid with
sodium hydroxide remember to add
phenolphthalein so we know the endpoint
of the titration
can you remember the correct color
change
pause and resume when ready
phenolphthalein goes from colorless to
light pink at the end point
however we don't want pink crystals so
we must make note of the amount of
sodium hydroxide used in the initial
titration and repeat the titration
without phenolphthalein
here is a challenge can you write the
equation for this reaction just as we
did in the first example
use a piece of paper and a pencil pause
the lesson and resume when ready
the answer is
this is a double displacement reaction
whereby the hydrogen and sodium ions
have switched
as sodium chloride is soluble in water
what we get is a solution of sodium
chloride this is also an acid-based
neutralization reaction yielding a salt
and water
now we can evaporate as much water as
possible and let sodium chloride
crystallize over the next few days in a
crystallizing dish
unlike the copper ii sulfate crystals
sodium chloride crystals are white
smaller and have a cubic like structure
so there you have it
two soluble salts have been made by
acid-base neutralization and isolated to
recap we can form soluble salts by the
reaction of an insoluble base with an
acid and the reaction of a soluble base
or an alkali with an acid
you