Double Displacement Reactions - Weeblyghsacceleratedchemistry.weebly.com/uploads/1/0/5/4/10549360/ch.… · Double Displacement Reactions Will you find the PPT? I’ll give you six

DDR

Double Displacement Reactions

Will you

find the

PPT?

I’ll give you

six clues.

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!

Clue # 2:

DDR has a pattern

I’d say we

have a pretty

“solid”

relationship.

Do I hear

wedding

bells?

“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).

What does (aq) mean?

Why is (aq) superscripted after

the formula 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.

Solutions with an “alibi”Pink Yellow Grey Blue-green

NaNO3 KNO3 Co(NO3)2 K2CrO4

NaBr KCl FeCl3 K2SO4

Na2CO3 NaCl KOH

Na2SO4 CoCl2

BaCl2 NaOH

AgNO3

Add more to the list if the “products” of a combination = NR