Chem. 319 Ms. Hobbie
In this experiment, you will study two major classes of aqueous chemical reactions. The first class of reactions is called metathesis, or double replacement, reactions. Metathesis reactions incorporate precipitation, some acid/base, and gas-forming reactions. In the simplest of terms, a metathesis reaction involves the switching of ion partners between two ionic compounds.
When will a metathesis reaction occur?
Metathesis reactions occur when a precipitate, a gas, a weak electrolyte or non-electrolyte is formed.
Each of these types of products is considered a “driving force” for the reaction; because they are produced, the reaction will proceed.
You must learn how to predict whether the reactants present in solution, when mixed, will result in the production of one of these driving forces.
You can predict whether or not ions in solution might react with other ions to form a precipitate by utilizing a solubility table:
1.
All common compounds containing
alkali metal ions and ammonium ion
(NH
4+
) are soluble.
2.
All common nitrates (NO
3-
), acetates
(CH
3
COO ), and perchlorates (ClO are soluble.
4-
)
3.
All common chlorides (Cl – ), bromides
(Br – ) and iodides (I – ) are soluble
4.
except those of Ag + , Pb 2+ and Hg
22+
.
All common sulfates (SO
42-
) are soluble except those of Ag + , Pb 2+ and
Hg
22+
and also Ca 2+ , Sr 2+ and Ba 2+
1.
All common metal hydroxides are insoluble,
except those of Group 1A(1) and Ca 2+ (slightly soluble), Sr 2+ and Ba 2+ .
2.
All common carbonates (CO
32-
), sulfites, (SO
32-
),
phosphates (PO
43-
) and chromates (CrO
42-
) are insoluble, except those of Group 1A(1) and NH
4+
.
3.
All common sulfides are insoluble except those of
Group 1A(1), Group 2A(2) and NH
4+
.
The formation of a weak electrolyte is the third type of driving force in the metathesis reaction group.
A weak electrolyte is classified as a species that dissociates very little in aqueous solution.
It is helpful to know a short list of acids that are strong electrolytes (dissociate virtually 100% in aqueous solution).
Strong Acids Ionization Products
HCl, HBr, HI
HNO
3
HX → H
HNO
3
+ + X –
→ H + + NO
3–
H
2
SO
4
HClO
4
H
2
SO
4
→ H + + HSO
4–
NOTE the products here!
HClO
4
→ H + + ClO
4–
With this list known, one can safely assume that all other acids are weak electrolytes.
(see the next page for an example…)

Formation of a Weak Electrolyte Example:
KF(aq) + HBr(aq)  HF (aq) + KBr(aq)
K + (aq) + F (aq) + H + (aq) + Br (aq)  HF (aq) + K + (aq) + Br (aq)
H + (aq) + F (aq)  HF (aq)
 It is important to remember that acid/base neutralization reactions fall into this category. Water is a non-electrolyte 1 and is therefore a driving force in a neutralization reaction between a strong acid and a strong base.
Metathesis reactions that result in the formation of a gas are tricky to predict. In fact, it requires a bit of memorization to anticipate the production of a gas. Below is a table of reactions that typically result in the formation of a gas. The gas can either be formed directly during the course of the reaction or an unstable molecular species might be formed first and then decomposes into the gas form.
Gases that are formed in metathesis reactions
Gas
Required Reactants
(and Indicating Properties)
CO
2 carbonate compound + acid
(many bubbles)
Typical Reaction
SO
2 sulfite compound + acid
(some fizzing, stinging sensation in nose)
H
2
S sulfide compound + acid
(distinctive, unpleasant smell)
HCN cyanide compound + acid
(dangerous gas)
NH
3 ammonium compound + strong base
(distinctive smell)
K
2
CO
3
+ 2HCl  H
2
CO
3
+ 2KCl
NOTE: H
NIE: CO
32-
2
CO
3
 H
2
O(l) + CO
(aq) + 2H + (aq)  H
2
2
(g)
O(l) + CO
2
(g)
K
2
SO
3
+ 2HCl  H
NOTE: H
2
SO
3
2
SO
3
+ 2KCl
 H
2
O(l) + SO
2
(g)
NIE: SO
32-
(aq) + 2H + (aq)  H
2
K
2
S + 2HCl  H
2
S(g) + 2KCl
O(l) + SO
2
(g)
NIE: S 2(aq) + 2H + (aq)  H
2
S(g)
NaCN + HCl  HCN(g) + NaCl
NIE: CN (aq) + H + (aq)  HCN(g)
NH
4
Br + KOH
Net: NH
4+
 NH
3
(g) + H
2
O(l) + KBr
(aq) + OH (aq)  NH
3
(g) + H
2
O(l)
1 Water is in reality a very weak electrolyte… but for the time being it will be classified as a nonelectrolyte.

In this experiment, mix about 1 mL portions of 0.1 M aqueous solution of each reagent in small test tubes, unless otherwise directed. If there is no reaction, simply write N.R.
Part I: Thinking about the reaction first and then performing the reaction
For each of the following mixtures, try verbally predicting the net ionic equations with your partner
(and sketch out the answers where you find space below). Then perform the reactions as directed and report any observations that confirm your prediction.
1. Precipitation: copper(II) sulfate + barium chloride
 Predicted net ionic equation: ______________________________________________________________
 Perform the reaction.
 Observations that support your identification of a driving force?
2. Weak-acid formation: 0.1 M hydrochloric acid + sodium acetate
 Predicted net ionic equation: ______________________________________________________________
 Perform the reaction TWICE. The second time, use a watch glass with a quarter-size squirt of sodium acetate. Monitor the conductivity while adding 0.1 M hydrochloric acid DROPWISE.
 Observations that support your identification of a driving force?
3. Neutralization: 0.1 M sodium hydroxide + sulfuric acid
 Predicted net ionic equation: ______________________________________________________________
NOTE: sulfuric acid is a strong acid, but the ions it creates are H + and HSO remembering…
4–
. This is worth
 Perform the reaction TWICE. The second time begin with 0.1 M sodium hydroxide in the test tube and add two drops of universal indicator. Monitor the color while adding the acid
DROPWISE.
 Observations that support your identification of a driving force?
4. Gas-forming: sodium carbonate + 1.0 M hydrochloric acid (The handout is helpful here.)
 Predicted net ionic equation: ______________________________________________________________
 Perform the reaction.
 Observations that support your identification of a driving force?

Part II: Observing the reactions and then thinking
Perform the following reactions and record your observations. Not sure if a reaction has occurred?
Consider monitoring conductivity or universal-indicator color changes.
WHEN IN DOUBT… you will find the information sheet very helpful. Dive into it!
1. copper(II) sulfate + sodium phosphate observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation ______________________________________________________________________
2. (Mix these reactants IN THE HOOD. Waft momentarily…) sodium sulfide + 1.0 M hydrochloric acid observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
3. potassium chloride + sodium nitrate observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
4. solid sodium hydrogen sulfite + 1.0 M hydrochloric acid (Waft carefully, then more forcefully…) observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
5. 0.1 M sodium hydroxide + 0.1 M hydrochloric acid observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
6. 1.0 M sodium hydroxide + 1.0 M ammonium chloride (Waft carefully, then more forcefully…) observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________

7. silver nitrate + 1.0 M hydrochloric acid observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
8. Sulfuric acid + sodium acetate observations _____________________________________________________________________________ molecular equation ______________________________________________________________________ full ionic equation _______________________________________________________________________ net ionic equation _______________________________________________________________________
Do one more precipitate… maybe a lead or silver one that turns brown/black? Most of these are colorless, so not very excititng. Also, consider NOT doing the sulfur dioxide… nasty stuff.
Additional Questions
No Collaboration – this should be your own work. You may hand-write your answers.
1.
Predictions. When the following substances are mixed, if a reaction will occur, write the formula and net ionic equations for the reaction. If no reaction occurs, write N.R. a.
Nitric acid solution and solid barium carbonate. b.
Zinc chloride and lead(II) nitrate solutions. c.
Acetic acid and strontium hydroxide solution. (Careful with the net ionic equation… there is a weak acid among the reactants!) d.
Ammonium chloride and potassium hydroxide solutions. e.
Potassium cyanide solution and sulfuric acid. (Careful with the net ionic equation… sulfuric
2.
acid is among the reactants!)
A solubility rules puzzle. Suppose that you have a solution that might contain any or all of the following cations: Cu 2+ , Ag + , Ba 2+ and Mn 2+ . To this unknown solution, you add an excess of HCl. which causes a precipitate to form. After the precipitate is filtered off, excess H
2
SO
4
is added to the filtered solution (called the “supernatant” liquid) and another precipitate forms. This precipitate is also filtered off. Finally a solution of NaOH is added to the supernatant liquid until it is strongly basic, but no precipitate appears. a.
What is the identity of each of the precipitates? b.
Which cations are not present in the original solution? How do you know?
3.
Creating desired products. Write a balanced chemical equation showing how you could create each of the following salts as directed. Note: There may be more than one possible answer.
4.
a.
potassium chloride from an acid/base reaction b.
barium sulfate from a precipitation reaction c.
sodium nitrate from a gas-forming reaction
Stoichiometry: When 5.0ml of 0.10 M silver nitrate is mixed with 2.0ml of 0.20 M sodium sulfide solution, what will be the theoretical yield of the solid and molar concentration of the excess ion?
Show your work.