Intro to Chemistry Chem1020 Lab
Ionic Precipitation Reactions
in Aqueous Solutions
Chemistry Department
Minneapolis Community & Technical College
1
Overview
• Part I: Procedure
Introduction
Station setup
Mixing
Waste disposal
• Part II: Lab report
2
Part I. Procedure
You will be mixing 14 pairs of chemicals in aqueous solutions.
Observe whether there is a precipitation reaction between the two
solutions in each pair. Write the chemical equations for the
reactions. This part is discussed in Chapter 7.2 & 7.3 in textbook.
The 14 test tubes provided
for you will be used for the
14 pairs of chemicals. Make
sure to use the correct test
tubes.
For example: test tube #5
needs to be used for the
reaction #5: strontium
chloride solution with
aluminum sulfate solution.
3
Station Setup
There will be 14 stations. A typical station looks like this:
Used and rinsed
test tubes
(pointing up)
Waste
container
Water for rinsing
used test tubes
A pair of chemicals
4
Mixing Chemicals
1. Choose the correct test tube. Add 3
drops of each of the two chemicals in
that reaction.
2. Make sure not to let the tip of the
dropper touch the test tube
(especially the inside) to avoid
contamination. Put the dropper back
to its original container.
3. Mix the chemicals by gently
plucking the bottom of the test tube.
Do you observe any signs of a
precipitation reaction? If yes, record
the color and form of the precipitate,
e.g. white gel-like.
5
Waste Disposal
• Don’t mix wastes, or dump them into
the sink!!!
• Dispose of the waste from a reaction into
the waste container located in the station
designated for that reaction.
• Rinse the test tube with water and
dispose of the rinse into the same waste
container.
Please restock your test tube rack with 14 clean and dry
test tubes for the next section. Thanks!
6
Part II. Lab Report
This lab report takes a significant amount of time to finish unless you
are very proficient in writing formulas and chemical equations. Make
sure to start early, and work on one part at a time. Review the formulas
of the polyatomic ions before you start. Try not to refer to textbook or
lecture notes, and use the periodic table and solubility rules only.
1. Complete the names of the products:
1) Switch the two cations
2) Check the solubility rules for the solubilities of the two products
Example:
Reaction #14: Sodium hydroxide and magnesium chloride
sodium hydroxide + magnesium chloride 
magnesium hydroxide (s) + sodium chloride
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2. Balanced molecular equation:
1) From the above equation with names of compounds, translate the names
of the ions into their formulas
2) Determine the formula of each compound based on the charges of its
cation and anion
3) Balance the equation
4) Indicate the physical state of each compound based on the solubility
rules. “s” for solid (insoluble), and “aq” for soluble.
*To receive points for this part, you need to have correct formulas for all
reactants and products, their physical states, and coefficients.
Example:
1) sodium hydroxide + magnesium chloride magnesium hydroxide (s) + sodium chloride
Na+
OH-
Mg2+
2)
NaOH
+
MgCl2
3)
2 NaOH
+
MgCl2
4)
2 NaOH (aq) +
Cl-
MgCl2 (aq)
Mg2+



OH-
Na+
Cl-
Mg(OH)2
+
NaCl
Mg(OH)2
+
2 NaCl
Mg(OH)2 (s)
+
2 NaCl (aq)
The parts in green are the ones being accomplished in that step. You are only required to
show the final balanced equation.
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3. Net ionic equation:
1) From the above balanced molecular equation, select the insoluble
product (having “s” as its physical state). Write down its formula on
the right side of the equation
2) Write the formulas of its cation and anion on the left side of the
equation.
3) Balance the equation
4) Indicate the physical state of ions as “aq” and that of the product as “s”
*To receive points for this part, you need to have correct formulas for all
reactants and products, their physical states, and coefficients.
Example:
 Mg(OH)2
1)
 Mg(OH)2
3) Mg2+ + 2 OH Mg(OH)2
4) Mg2+ (aq) + 2 OH- (aq)  Mg(OH)2 (s)
2)
Mg2+
+
OH-
The parts in green are the ones being accomplished in that step. You are only
required to show the final balanced equation.
9