Chemistry Lab Conservation of Mass
The law of conservation of mass states that in a chemical reaction, matter is neither
created nor destroyed. Stating the law another way, the total mass of the reactants is the
same as the total mass of the products. In this laboratory investigation, you will perform
three reactions and observe how this law is valid under ordinary laboratory conditions.
You will do this by comparing the masses present before the reaction with the masses
present after the reaction.
Objectives
1. Measure the mass of reactants before a reaction and the mass of the products after
the reaction.
2. Calculate the percent difference of mass before and after the reaction
3. Evaluate the validity of the law of conservation of mass under the ordinary
laboratory conditions.
Materials
Apparatus
Reagents
Balance
0.1 M sodium sulfate solution Na2SO4(aq)
Beakers
0.1 M strontium chloride solution SrCl2(aq)
Test tubes
Potassium iodide solution KI(aq)
Rack
Lead (II) nitrate solution Pb(NO3)2(aq)
10 ml graduated cylinder
Sodium nitrate NaNO3 (s)
Procedure
Part 1.
1.
2.
3.
4.
Put on safety goggles and laboratory apron.
Place about 2.0 mL of 0.1M sodium sulfate solution Na2SO4 (aq) in a test tube.
Clean the graduated cylinder thoroughly and rinse it well with distilled water.
Place about 2.0 mL of 0.1M strontium chloride solution, SrCl2 (aq), in another test
tube.
5. Place the test tubes with their contents in a small beaker. Determine the total mass of
the solutions, test tubes, and beaker. Record the total mass in Table 1.
6. Pour the strontium chloride solution into the test tube containing the sodium sulfate
solution. Record observations for the chemical reaction.
7. Place the product test tube and the empty test tube in the small beaker. Mass the two
test tubes, the beaker, and the reacted solution. Record this combined product mass in
Table 1.
Part 2.
1. Place 10.0 mL of water in a test tube.
2. Obtain a capped test tube containing a sample of sodium nitrate solid, NaNO3(s),
from your teacher.
3. Place the test tubes with their contents in a small beaker. Determine the total mass of
the solutions, test tubes, and beaker. Record the total mass in Table 1.
4. Add the water to the sodium nitrate, recap the test tube firmly, and shake the mixture
until the sodium nitrate dissolves. Feel the test tube and record observations.
5. Place the product test tube and the empty test tube in the small beaker. Mass the two
test tubes, the beaker, and the reacted solution. Record this combined product mass in
Table 1.
Part 3
1.
2.
3.
4.
Place about 2.0 mL of potassium iodide KI (aq), in a test tube.
Clean the graduated cylinder thoroughly and rinse it well with distilled water.
Place about 2.0 mL of lead nitrate, Pb(NO3)2 (aq), in another test tube.
Place the test tubes with their contents in a small beaker. Determine the total mass of
the solutions, test tubes, and beaker. Record the total mass in Table 1.
5. To minimize contamination, pour the potassium iodide solution into the flask
containing the lead nitrate solution. Record observations for the chemical reaction.
6. Place the product test tube and the empty test tube in the small beaker. Mass the two
test tubes, the beaker, and the reacted solution. Record this combined product mass in
Table 1.
Cleaning Up
1. Lead compounds are toxic. Place the lead product solution from Part 3 in the
receptacle located on the front desk. DO NOT POUR DOWN THE DRAIN.
2. Wash all other glassware in the sink and return it to its proper place.
3. Wash your hands thoroughly before leaving the laboratory.
Data Presentation
TABLE 1. Mass Recordings
Experiment
Total Mass Before Rx (g)
Part 1
Part 2
Part 3
Total Mass After Rx (g)
Data Analysis
1. Calculate the change in mass (mass after Rx - mass before Rx) for each part of the experiment.
Record the results in Table 2, below.
2. Calculate the percentage change in mass and record your results in Table 2 below.
[(change in mass) / mass before RX] x 100 = % change.
3. Be sure to include the calculations in the report.
TABLE 2. Percent Change in Mass
Experiment
Change in Mass (g)
Part 1
Part 2
Part 3
Percent Change in Mass (%)
Conclusions
1) Write the balanced chemical reaction showing reactants and products for Parts 1 and 3.
Be sure to predict solubility of the products.
2) Based on the data and calculations, was the law of conservation of mass found to be valid
in all three parts?
3) Suggest reasons why the data may not have confirmed the law in every part.
4) What observations were made for each of the three chemical reactions?
5) Give an example of a chemical reaction in which it would be essential to stopper (seal)
the reaction vessel in order to show conservation of mass?