Kitchen Chemistry Experiment
3
Law of Conservation of Matter
Can matter
be created or destroyed in a chemical reaction? This simple test
will show how the products of a chemical reaction will have the
same combined mass as the reactants before the chemical change.
| Materials |
Substitutions |
| solutions
of NaOH, CuSO4, NH4OH, and Na2CO3 |
solutions
made with Drano, ammonia, Bluestone algaecide, and washing soda |
| 4 graduated
cylinders |
4-2 oz
plastic cups |
| 3 150-mL
beakers |
3-5 oz
plastic cups |
| balance |
|
Procedure
- Pour
2 oz of NaOH solution into a small (2 oz) clean plastic
cup. Use another clean 2 oz cup to measure 2 oz of CuSO4
solution and pour it into a clean 5 oz cup.
- Carefully
place the two solutions on the balance, making sure the solutions
do not mix. Weigh the solutions and the cups together and record
the combined weight .
- Pour
the NaOH into the 5 oz cup with the CuSO4 solution. Allow the
solutions to mix. Describe what happens.
- Weigh
both cups and the mixture again. Record the new weight. By how
much did the weight change?
- Repeat
the process in # 1 and #2 above for the combinations listed in
the data section below. DO NOT ALLOW THE SOLUTIONS TO MIX UNTIL
AFTER YOUR FIRST WEIGHING. This precaution includes using the
same cup to measure the same solution each time. Do not mix up
the measuring cups.
Data
and Observations
1. Total
weight of NaOH and CuSO4 before __________g after _______g
2. Total
weight of NH4OH and CuSO4 before __________g after _______g
3. Total
weight of Na2CO3 and CuSO4 before __________g after _______g
Complete
the following equations:
4. NaOH
+ CuSO4 ----->_________________________________
5. NH4OH
+ CuSO4 ------->_____________________________
6. Na2CO3
+ CuSO4 ------->____________________________
Extensions
The substances
chosen for this lab are common and easy to find. You may want
to repeat this lab with solutions of BaCl2 and Na2SO4 , for example,
or KI and Pb(NO3)2.
1. What
is the insoluble solid that is produced?
2. Use
a solubilty chart to predict the identity of the insoluble product.
3. Use
the periodic table to prove that total formula mass is conserved.
Why is it important to balance a chemical reaction?
Teacher's
Notes
This experiment
verifies that matter can neither be created or destroyed, but
can be changed in form. Weight, or mass, does not change as a
result of chemical changes.
The balanced
equations are as follows:
4. 2NaOH
(aq) + CuSO4 (aq) -----> Na2SO4 (aq) + Cu(OH)2 (s)
5. 2NH4OH
(aq) + CuSO4 (aq) -------> (NH4)2SO4 (aq) + Cu(OH)2 (s)
6. Na2CO3
(aq) + CuSO4 (aq) -------> Na2SO4 (aq) + CuCO3 (s)
The insoluble
product that is formed is called a precipitate .
Solubility Tables can help students predict which product will
be insoluble (form a precipitate)
For additional
ideas on this concept, see Experiment #2 and the Teacher's Notes.
Solution
Preparation
The sodium
hydroxide can be obtained from Drano or Red Devil Lye. If you
use Drano, the solution does not need to be very concentrated
but you would want to filter the aluminum filings that are mixed
in with the pellets of NaOH. Lye is CAUSTIC so wear gloves and
wash all surfaces anyone might touch. Copper (II) Sulfate can
be purchased at a good hardware store as a algaecide (Bluestone)
or root eater. Solutions can be prepared directly and since this
is a precipitate reaction, the concentrations are qualitative
and approximate. Ammonium hydroxide is nothing more than household
ammonia. Use it straight out of the bottle from the grocery store.
Finally, the sodium carbonate can be purchased at the grocery
store as washing soda (Arm and Hammer) and can simply be mixed
with water to form a solution.
Safety
Precautions
As mentioned
in the solutions preparations section, sodium hydroxide is CAUSTIC
and shoud be handled carefully. Students may need to wear gloves.
The base will feel slippery on the skin and should be washed
immediately. Copper solutions can cause eye infections, so students
should wash their hands after handling these substances, too.
