double displacement reactions -...
TRANSCRIPT
For the D.D. Reaction to happen
one of the following must occur:
A solid precipitate
(PPT) must form
Clue #1:
We will only be looking for PPT formation in the DDR lab
Liquid water must be produced in the reaction.
A gas must form
Did you see it turn
chalky white when I
mixed
AgNO3 + BaCl2
?????
What if it
stays
clear?
Oh!!
No
Reaction!
“Double Displacement” means
two ions change places.
Na2CO3 + BaCl2 2 NaCl + BaCO3
Reactants Products
More on this in a minute…
Why did the ions switch places?
They find another ion they are more
strongly attracted to compared to a
water molecule.
Water can dissolve soluble ionic solids
like NaNO3. Polarity allows water to
slide between ions of opposite charge.
Water can dissolve soluble ionic solids
like NaNO3. Polarity allows water to
slide between ions of opposite charge.
O
The hydrogen side of H2O is positive and
the oxygen side is negative.
Insoluble solids or “precipitates” prefer
to stay in solid clumps rather than let a
“ .” slip between the ions.
Na+
Na+
Na+
Na+
Na+
NO3-
NO3-NO3-
NO3-
NO3-
NO3-
NO3- Light
passes
through
“clear”
solutionsNa+
Light
reflects off
insoluble
cloudy
“solids” or
PPT’s
Imagine there are water molecules between the ions.
“Double Displacement” means
two ions change places.
Na2CO3 + BaCl2 2 NaCl + BaCO3
Reactants Products
Clue # 3: Only one of the
products is the PPT
Na2CO3 + BaCl2 2 NaCl + BaCO3
Reactants Products
NaCl ? or BaCO3?
If NaCl is soluble, it cannot be a
PPT
Na2CO3 + BaCl2 2 NaCl + BaCO3
Reactants Products
How do you know if NaCl is soluble?
Clue # 4: If NaCl is
one of the reagent
bottles in the lab…and
the solution in the
bottle is clear…it is
enough evidence to
suggest it is always
soluble.
Solid NaCl crystals will dissolve into ions
in water to make NaCl (aq).
NaCl (aq).“(aq)” means Na+
and Cl- ions are
present in aqueous
solution.
“Aqueous” means
ions are dissolved
in between water
molecules.
Clue #5: If you can prove one of the
products is soluble, or one of the reagent
solutions,
then it is logical the other product is
GUILTY of being the insoluble PPT!
Hint: Precipitates often “fall out” of
solutions; so if you let it settle awhile the
PPT may be easier to detect.
Clue #6 :
If there is no reaction…
at least make note of the aqeuous
or soluble products.
(Switch the negative ions for any
combination to find new formulas of soluble
solutions)
BaCl2 + 2NaNO3Ba(NO3)2 +2NaCl
Add the formula(s) to the list of products
with an “alibi.”
Guilty verdicts need only be
“circumstantial” to complete this lab.