DOUBLE REPLACEMENT REACTIONS
1) THE OBJECTIVE OF THIS POWERPOINT IS TO LEARN THE
PROCEDURE OF PREDICTING DOUBLE REPACEMANT REACTIONS
AND TO APPLY THIS TO THE LAB YOU PERFORMED.
2) RESOURCES…YOU WILL NEED TABLE “F” SOLUBILITY
GUIDELINES, THE PERIODIC TABLE , CRISS CROSS METHOD AND
BALANCING SKILLS.
3) ASSIGNNING CHARGE RULES, CHARGE RULES YOU WILL NEED
ARE:
1) GROUP ONE IS ALWAYS +1
2) GROUP TWO IS ALWAYS +2
3) HALIDES(HALOGENS) in binary compounds are -1 (for now)
4) POLYATOMIC ION CHARGES ARE GIVEN ON TABLE “F”.
4) FACTS…(aq) is soluble, homologous aqueous phase.
(s) is solid, insoluble (one product. must be a solid)
EXAMPLE REACTIONS
1) FIRST…EXCHANGE THE METALS TO GET PRODUCTS
Na3 (PO4) (aq) + Ba(NO3)2
(aq)
Na3 (PO4) + Ba(NO3)2  Ba(PO4) +Na(NO3)
2) USE CRISS CROSS TO DERIVE CORRECT SUBSCRIPS OF
PRODUCTS.
REMEMBER,
SUBSCRIPTS OF ELEMENTS ARE NOT INHERETED
ACROSS THE ARROW.
NEVER CHANGE A POLYATOMIC ION FORMULA,
HOWEVER THE SUBSCRIPT OUTSIDE OF ITS PARENTHESIS IS
NOT INHERITED.
•
EXAMPLE REACTIONS
2) USE THE CRISS CROSS METHOD TO DETERMINE THE CORRECT
SUBSCRIPTS OF THE PRODUCTS.
•
Na3 (PO4) + Ba(NO3)2  Ba(PO4) +Na(NO3)
Ba(PO4)
Ba is in group 2
and is +2 each
Ba+2
Phosphate is -3
each (table E)
(PO4) -3
Na(NO3)
Na is in group 1
and is +1 each
Na+1
NO3 is -1 from
table E
(NO3) -1
Na1(NO3)1
Ba3 (PO4)2
Na(NO3)
Barium Phosphate
Sodium Nitrate
•
EXAMPLE REACTIONS
3) THIRD…WITH THE CORRECT PRODUCT SUBSCRIPTS IN PLACE, USE
TABLE “F” TO DETERMINE IF ONE OF THE PRODUCT SALTS IS
INSOLUBLE.
•
Na3 (PO4)(aq) + Ba(NO3)2(aq)  Ba3(PO4)2 (s) +Na(NO3)(aq)
From table “F” all Phosphates are
insoluble, Barium is not an
exception.
All nitrates are soluble, no exceptions
4) Now its time to balance…your favorite! Use MINOH…
M – balance metals first
I – balance polyatomic ions second
N- Balance non metals
O-balance oxygen
H-balance hydrogen
EXAMPLE REACTIONS
4)BALANCE( MINOH pt 1)---BALANCE METALS
•
Na3 (PO4)(aq) + 3 Ba(NO3)2 (aq)  Ba3(PO4)2 (s) + 3 Na(NO3)(aq)
4) BALANCE(MINOH pt 2)---BALANCE IONS (POLYATOMIC IONS)—(THERE
ARE NO NONMETALS TO BALANCE SO WE GO DIRECTLY TO IONS.)
•
2 Na3 (PO4)(aq) + 3
Ba(NO3)2 (aq)  Ba3(PO4)2 (s) + 3 Na(NO3)(aq)
THE COEFFICIENT
2
BALANCES THE 2 PHOSPHATES ON THE RIGHT
2 Na3 (PO4)(aq) + 3 Ba(NO3)2 (aq)  Ba3(PO4)2 (s) + 63 Na(NO3)(aq)
THE COEFFICIENT 6
BALANCES THE 6 NITRATES ON THE LEFT AND THE
6 SODIUMS ON THE LEFT. BALANCED NOW!
NOW…DETERMINE THE IONIC REACTION…
DISSOCIATE THE (aq) SALTS.
2 Na3 (PO4)(aq) + 3 Ba(NO3)2 (aq)  Ba3(PO4)2 (s) + 6 Na(NO3)(aq)
6 Na+ + 2 (PO4)3-
+ 3 Ba+2 + 6 (NO3)-

Ba3(PO4)2 (s)
+ 6 Na+ + 6 (NO3)-
FINNALY….cancel spectator ions (ones that did not change
phase) to derive NET IONIC REACTION
6 Na+(aq)+ 2 (PO4)3-(aq) + 3 Ba+2 (aq) + 6 (NO3)- (aq)

Ba3(PO4)2 (s)
+ 6 Na+ (aq) + 6 (NO3)- (aq)
THE NET IONIC EQUATION IS …………………..
2 (PO4)3-(aq) +
3 Ba+2 (aq)

Ba3(PO4)2 (s)