Name ______________________
Hour _______Due Date________
Chemistry Lab # 5
(Conservation of Mass)
Discussion
Matter cannot be created nor destroyed by a chemical change. This very important
principle is known as the Law of Conservation of Mass. This law applies to ordinary
chemical reactions (as opposed to nuclear reactions, in which matter can be changed to
energy). During a chemical change (reaction), the atoms of one or more substances
(reactants) simply undergo “rearrangements”. The result of these rearrangements is the
formation of new, different substances (products). All of the original atoms are still
present. It is because of the law of conservation of mass that we are able to write
balanced chemical equations. Such equations make it possible to predict the masses of
reactants and products that will be involved in a chemical reaction.
In this experiment, aqueous solutions of three different compounds will be used to
produce two separate and distinct chemical reactions. This experiment will give you a
better understanding of the law of conservation of mass and its importance in chemistry.
Objective
The student will determine whether mass is conserved in a particular set of chemical
reactions. Also, the student will observe evidences for chemical reactions.
Materials
Balance (.01 g)
Graduated Cylinder (10 mL)
Test Tubes (2-small)
Apron
Sodium Carbonate Solution [Na2CO3 – 1 M]
Sulfuric Acid [H2SO4 – 1 M]
Crucible
Ringstand
Pipestem Triangle
Spark Lighter
Erlenmeyer Flask (50 mL)
Rubber stopper (3-flask & test tubes)
Rubber gloves (for handling acid)
Calcium Chloride [CaCl2 – 1 M]
Magnesium (Mg) Strip
Ring
Bunson Burner
Tongs
Safety Goggles
* Handle the acid with care, it is caustic and corrosive. If you spill it on you, rinse with
lots of water and tell your teacher.
Procedure
Preparation
1.
In a graduated cylinder, measure exactly 10.0 mL of sodium carbonate solution.
Pour into a clean, dry 50 mL Erlenmeyer flask. Stopper the flask and then rinse
and dry the graduated cylinder.
2.
Measure exactly 3.0 mL of calcium chloride solution and pour into a clean, dry
test tube. Stopper and label the tube. Rinse and dry the graduated cylinder.
3.
Repeat step 2 with 3.0 mL of sulfuric acid solution.
4.
Put the stoppered test tubes in a 50 mL beaker, and place the beaker + test tubes
and the stoppered Erlenmeyer flask on the balance. Measure the mass and record
in the data table.
Reaction A
5.
Remove from balance. Remove the stoppers from the calcium chloride test tube
and the sodium carbonate flask. Pour the calcium chloride solution from its test
tube into the sodium carbonate flask. Swirl thoroughly to mix the two solutions
and record observations.
6.
Put the stoppers back on the proper containers. Place the beaker + stoppered test
tubes and the stoppered flask on the balance again to measure the mass. Record
mass in data table.
Reaction B
7.
Remove from balance. Pour the sulfuric acid solution from its test tube into the
flask. With the stopper off, swirl the flask until bubbling stops. Record
observations.
8.
Put the stoppers back on the proper containers. Remeasure the mass as in steps 4
&6 (beaker + stoppered test tubes, flask, stopper for flask). Record mass in data
table.
Reaction C
9.
Obtain a strip of magnesium metal. Roll it into a fairly tight coil.
10.
Set up a ringstand, ring, and a pipestem triangle.
11.
Obtain a crucible. Wash and dry the crucible. The crucible should be handled with
tongs once clean.
12.
Put the magnesium coil in the crucible, measure the mass, and record in the data
table.
13.
Place the crucible on the pipestem triangle and heat it with a very hot bunson
flame for several minutes, until the chemical reaction is complete. Make
observations.
14.
Using tongs, place the hot crucible on the base of the ringstand to cool.
15.
Once the crucible is cooled, measure the mass and record in the data table.
16.
Clean, dry, and put all equipment away. Wash hands with soap and water. Lab
stations should be clean and clear of equipment.
Observations
* Remember: observations should include a complete description of the reactants
before the reaction itself, and the products left over.
Reaction A
Reaction B
Reaction C
Data
Mass (g)
* Mass of Beaker, Erlenmeyer Flask, Stoppers, Test Tubes, & Contents …
- Before Mixing
________
- After Mixing Calcium Chloride & Sodium Carbonate (Reaction A)
________
- After Mixing Sulfuric Acid (Reaction B)
________
* Mass of Crucible + Magnesium Coil
________
* Mass of Crucible + Residue (Reaction C)
________
Conclusions & Questions
1. What indications that a chemical reaction was taking place did you observe for …
a) Reaction A
b) Reaction B
c) Reaction C
2. Why were you instructed to leave the flask unstoppered after the sulfuric acid
solution was added?
3. Compare the three masses in the data table after each reaction. Account for any
differences, if any.
Reaction A
Reaction B
Reaction C
4. Based on your results, does this experiment verify the law of conservation of mass?
Explain why or why not.
5. How might the experiment be improved?
6. When you burn a log in the fireplace, the resulting ashes have a mass less than that of
the original log. Account for the difference in mass.
7. Discuss the law of conservation of mass and how it relates to the balancing of
chemical equations. (extra credit- 1)
8. There were three chemical reactions taking place. Write the chemical reaction and
balance the chemical equation for the three reactions. (extra credit- 2)