- University of Virginia
- Physics Department
with Mixed Solutions
A Physical Science Activity
- 2003 Virginia SOLs
- observe a chemical change;
- recognize the indicators of a chemical change (color change, precipitate);
- observe a double replacement reaction;
- verify the Law of conservation of matter;
- gain practice in the following skills: observing, measuring, identifying,
The reaction taking place here is a double replacement reaction
or an ion-exchange reaction. In this type of reaction, two ionic compounds are
made into solutions and mixed together. The positive ion of one of the compounds
will react with the negative ion of the other and form a precipitate. When the
precipitate forms, the results are dramatic - a colorful insoluble blue solid
appears. The students will observe two liquids with a particular mass resulting
in a liquid and solid with the same mass.
In the Copper nitrate solution the positive ion is copper (Cu) and the nitrate
) is the negative ion. In the sodium hydroxide solution the sodium (Na) is the
positive ion and the radical (OH) is the negative ion. These two solutions form
the reactants in the chemical reaction. When mixed, an ion exchange occurs and
the copper and sodium switch places in the compounds. One of the products formed
after this exchange is copper hydroxide Cu(OH)
which is an insoluble, blue gelatin-like solid. The other product, sodium nitrate,
is also a solid but is soluble in water and will remain in solution undetected.
To print out the Student Copy only,
- 30mL of sodium hydroxide prepared in advance
- 5 grams of cupric nitrate powder
- Two 100 mL beakers
- Paper for weighing chemicals
- Stirring rod
- Graduated cylinder
A 0.5 molar solution of sodium hydroxide is required to perform
this experiment. Measure out 20.0 grams of sodium hydroxide pellets
and dissolve them in 500 mL of water.
This will be enough for a class of 20 students working in pairs.
You can provide a small container for each lab station and the
students can mass out 25 mL and return the remainder to a central
Copper nitrate can be dispensed from a central location or
distributed in small containers to each lab station. In any event the
students will have to mass out 4.8 grams.
50 grams should be enough for a class of 20 students working in
Caution: Avoid skin contact with
the sodium hydroxide pellets. Use rubber gloves while
preparing the solution.
Safety glasses and aprons should be used, avoid
touching or tasting chemicals.
- With your balance mass out 4.8 grams of copper nitrate on a
piece of paper.
- (When massing chemicals on most balances, paper or some
type of container must be used to keep the chemical from coming
in contact with the metal pan because the chemical may be
corrosive. The paper or container must be massed before placing
the chemical on it, and then again with the chemical on it. The
two masses must be subtracted to obtain the mass of the
chemical alone if using a triple arm balance. When using an
electronic balance the "tare" function will remove the mass of
the paper or container.)
- Measure out 25 mL of water in a graduated cylinder and pour it
into a 100 mL beaker.
- Empty the copper nitrate into the beaker of water and stir
until the mixture is completely dissolved. Let the beaker and
solution remain on the balance.
- Place the second beaker on the balance, measure out 25 mL of
the sodium hydroxide solution.
- While both solutions are on the balance in separate
containers, record the mass. Enter the value in the data section
below under "mass of beakers and contents before reaction."
- Pour one of the beakers into the other, observe the reaction
and record the mass of both the empty and full beakers again.
Enter the value in the data section below under "mass of beakers
and contents after reaction."
To print out the Data Sheet only,
Mass of Beakers and Contents Before
Mass of Beakers and Contents After
- Describe the solution that was made when you mixed
copper nitrate in water.
- Describe the appearance of the sodium hydroxide
- What did you observe when you mixed the two solutions
- Describe the state of matter, color and solubility of
the new substance formed.
- A double replacement reaction is also called a ion
exchange reaction. Describe the exchange of ions that is
- In a double replacement reaction one product must
always be an insoluble solid. Which of the products
formed in this reaction is the insoluble solid?
- In a double replacement reaction one of the products
must always be a soluble solid. Which of these products
is the soluble solid?
- Describe what would happen if the products you
obtained in this reaction were filtered through filter
Students can perform the experiment, filter the product to separate the precipitate
from the soluble solid. Then evaporating the remaining solution on a hot plate
will yield the white powder sodium nitrate.
Students with special needs
Click here for information
on laboratories with students with special needs.
1. Which of the following equations is a double replacement
a. 2CO ==> 2C + O2
b. 2Na + 2H2O ==> 2NaOH + H2
c. 2Al + 3Cl2 ==> 2AlCl3
d. Na2CO3 + Ca(OH)2
==> CaCO3 + 2NaOH