Double
Replacement Reactions
A typical double replacement
reaction can occur when two ionic compounds are mixed together. In water these ionic compounds split apart
into their respective anions and cations.
The cations now have an opportunity to swap anions. A reaction occurs if , by swapping anions, a
product is formed that cannot split apart into anions and cations. Look at the following example: the reaction of silver nitrate and potassium
chloride. The silver, nitrate,
potassium and chloride ions all begin in solution. When a silver ion combines with a chloride ion, it leaves the
solution and becomes a solid. This
drives the reaction to completion!!!
AgNO3(aq) +
KCl(aq) ‑‑‑‑> AgCl(s) + KNO3(aq)
The reaction must be driven
by one of three driving forces:
Formation of a solid, formation of a gas or formation of a weakly‑ionizing
compound such as water. Lets look to
see what happens when the driving forces are not there.
NaNO3(aq) +
KCl(aq) ‑‑X‑‑>
NaCl(aq) + KNO3(aq)
Nothing happens!! Without a driving force there is no change
in the solution so we say no reaction has taken place. Note that even though we can write an
equation for the reaction, no reaction takes place without a driving force!!
How can we tell if an ionic
compound will be soluble in water?
There are a series of guidelines in your book. On the next page I provide you with another presentation of these
same rules:
Solubility
Rules
1.
All compounds containing Na+, K+, or NH4+ ions are soluble in
water.
2. All nitrates (NO3‑) are soluble in water.
3.
Most chlorides (Cl‑ ), and sulfates (SO42‑)
are soluble. Some important exceptions
are silver chloride (AgCl), barium sulfate (BaSO4), and lead sulfate
(PbSO4) which are insoluble.
4.
Most carbonates (CO32‑), phosphates (PO43‑),
sulfides (S2‑), and hydroxides (OH‑) are
insoluble in water. Important
exceptions are those of Na+, K+, and NH4+, as well as
barium hydroxide, Ba(OH)2.
How do you know if a gas
will form? If H2CO3 is
formed it will form a gas by decomposing to H2O and CO2. You will see that in this lab. Other compounds that release water or a gas
are
NH4OH and H2SO3.
When an strong acid and a
strong base react, in an aqueous solutions, they produce a salt and water. This is an example of a double displacement
reaction where the driving force is the formation of the covalent compound
water. Often, the only way to tell if
one of these reactions has occurred is by looking for the formation of heat or
by using an acid/base indicator to tell if the base has neutralized the
acid. If you do not see a reaction
occurring you may wish to ask your instructor for an appropriate
indicator. (How can you tell what the
color of the indicator will be in an acidic solution and a basic solution? Answer:
Test the solutions individually.)
Procedure
There are ten stations. Please use the standard procedure at each
station.
I. Reacting CuSO4 solution with NaOH
solution.
II. Reacting Na2CO3
solution with HCl solution.
III. Reacting KCl solution with Na2CO3
solution.
IV. Reacting Na2SO4
solution with BaCl2 solution.
V. Reacting NaOH solution with HCl
solution. (Use phenolphthalein
indicator)
VI. Reacting Na2CO3
solution with CaCl2 solution.
VII. Reacting Ni(NO3)2
solution with NaOH solution.
VIII. Reacting
Na2SO4 solution with Cu(N03)2
solution.
IX. Reacting KOH solution with MgCl2
solution.
X. Reacting NaHCO3 solution with HNO3
solution.
Standard
procedure
1. Transfer
10‑15 drops of one solution into test tube. Record in your notebook a description of the appearance of the
first solution.
2. Record
in your notebook your description of the second solution.
3. Using
a Beral pipet, add 10‑15 drops of the second solution to the test
tube. Record in your notebook your
description of the appearance of the reaction mixture. Dispose of waste appropriately,
4. a. Write in your notebook a complete, molecular
equation, including states.
b. Write in
your notebook the driving force and make sure that the equation is balanced.
c. If you
have covered total ionic equations and net ionic equations in class, write
these in your notebook as well.
Instant Lab Report
Name ________________
CHM 1025c
Double replacement Reactions
Purpose: To observe double replacement reactions, and from these
observations, determine the products and driving forces for each.
Procedure: As stated in lab handout and as presented by the instructor. All reagents had a concentration of 1 M.
Data and
Discussion:
Reaction 1 :
CuSO4 & NaOH
Driving force formation of
a solid
Observations
Molecular Equation:
Total Ionic equation:
Net Ionic Equation:
Reaction 2 : Na2CO3 & HCl
Driving force
____________________
Observations
Molecular Equation:
Total Ionic equation:
Net Ionic Equation: