Period:
Name:
Date:
LAW OF CONSERVATION OF MASS LAB INVESTIGATION
PRELAB
Please answer the following questions on a separate piece of paper using complete
sentences.
1.
Define the law of
conservation of mass.
2.
Using the periodic table
list the symbol and name of each element compromising the compounds in the 2
reactions below. (Ex. Na is sodium)
3.
Find the chemical
formulas for the following: Sodium carbonate, calcium chloride, sulfuric acid and
calcium carbonate.
4.
How could we find the
mass of just the CaCO3 (s) after the first reaction has occurred? That is, how
could the solid be separated from solution? Suggest two methods.
Introduction
Matter can be neither created or 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 where matter can be
changed to energy). During a chemical reaction, the atoms of one or more substances,
known as the reactants, undergo some “rearrangements.” The result of these
rearrangements is the formation of new substances, known as 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. The changes that will
occur during the reactions will be readily observable. Balanced chemical equations for
the two reactions are:
Reaction1:
NA2CO3 (aq) + CaCl2 (aq)
2 NaCl (aq) + CaCO3 (s)
Period:
Name:
Date:
Reaction 2:
CaCO3 (aq) +H2So4 (aq)
CaSO4 (s) + H2O (l) + CO2 (g)
The combined masses of the three solutions ( and their containers) will be measured
before and after each reaction has occurred. This experiment should give you a better
understanding of the law of conservation of mass and its importance in chemistry.
Objective
To determine if mass is conserved after two reactions have been completed.
Materials
Balance, 50ml Erlenmeyer flask, 2 small test tubes and stoppers to fit, 10 ml of sodium
carbonate solution, 3ml of calcium chloride solution, 3ml of 3M (3molar) sulfuric acid .
Procedure
Preparing the solutions
1.
Pour 10ml of the sodium
carbonate solution into the 50ml flask and stopper it.
2.
Pour the 3ml of calcium
chloride into a test tube and stopper it. Label your test tube.
3.
Pour 3ml of dilute sulfuric
acid into a second test tube and stopper that. Label the tube.
4.
Make sure that the
exteriors of the tubes are dry.
5.
Place the stoppered flask
and tubes on the balance and record the total mass.
Reaction1
1.
Carefully pour the
calcium chloride solution into the flask.
2.
Swirl gently to mix and
note any changes that occur.
3.
Stopper the flask and test
tube.
Period:
Name:
Date:
4.
Determine and record the
total mass of the flask and two test tubes.
Reaction 2
1.
Carefully pour the acid
into the flask.
2.
3.
Swirl gently to mix.
Continue to swirl until all
evidence of a chemical reaction has disappeared.
4.
If the flask is not at room
temperature, wait a few minutes until it is.
5.
Stopper the flask and the
test tubes.
6.
Determine the total mass
of the flask and the two test tubes.
Data and Observations
Data and unit
Total mass of flask, test tubes,
solutions and stoppers before mixing
Total mass after reaction 1 (include all
glassware and stoppers)
Total mass after reaction 2(include all
glassware and stoppers)
Theoretical mass after reaction2 =
initial mass
% error
Observations of reaction1:
Observations of reaction2:
Calculations
1 calculate the percent error of your data using the equation
l theoretical – experinamental l X 100
theoretical
where the theoretical value is the total mass of the chemicals before mixing.
Summary
Period:
Name:
Date:
Please discuss your qualitative observations, your %error, and whether or not
your data demonstrated that mass is conserved. Account for any losses in mass
and suggest ways to account for such errors in the future.
Post Lab Questions
1.
Look at the reactions in
the introduction section, what can you say about the number of atoms of each
element on each side of the reaction?
2.
What indications that a
chemical reaction was taking place did you observe after reaction 1 and 2.
3.
When you burn a log in a
fire place, the resulting ashes have a mass less than that of the original log.
Account for the difference in mass.
4.
Before Antoine Lavoisier
quantified his data which led to the law of conservation of mass, the
phlogiston theory existed as a reason for the change in mass in burning
materials (like the log in question #3). What is phlogiston?
5.
If 25.0 grams of H2 (g)
react with O2 (g) nto form 100.0 ml of H2O, what is the mass of O2 gas
needed? Write the chemical reaction that occurs.
6.