Conservation of Mass Lab

Question: Do substances lose or gain mass during chemical reactions?
Materials:
electronic balance 100 ml graduated cylinder
glass jar with lid Alka-Seltzer tablet


Procedure 1: With lid
1. Using the graduated cylinder, measure 50 ml of water and pour into the jar & put the top on the jar.

2. DO NOT PUT THE TABLET IN THE WATER - Using the electronic balance, measure the total mass of half an Alka-Seltzer tablet and the glass bottle containing 50 ml of water with the lid on. Put the tablet on top of the lid. Write the mass in the data table.

3. On the table, open the bottle and put tablet in the water. Quickly put the lid on and tighten.

4. Allow the tablet to dissolve completely.

What do you observe? ______

5. Do not remove the lid. Measure the mass of the bottle, water, and dissolved tablet and record in the table.

Procedure 2: Without lid

1. Clean your jar out thoroughly & dry it off.

2. Using the graduated cylinder, measure 50 ml of water and pour into the jar

3. DO NOT PUT THE TABLET IN THE WATER - Using the electronic balance, measure the total mass of half an Alka-Seltzer tablet and the glass bottle containing 50 ml of water without the lid. Record in the second table.

4. Drop the tablet in the water and allow to dissolve completely.

5. Measure the mass of the bottle and water. Record in the second table.

Data:

Procedure 1: With Cap on Bottle

Mass of jar, lid, & ½ of the tablet
Before / Mass of jar, lid, & ½ of the tablet
After dissolving / Difference between the masses (before – after)

Procedure 2: Without Cap on Bottle

Mass of jar & ½ of the tablet
Before / Mass of jar & ½ of the tablet
After dissolving / Difference between the masses (before – after)

Questions:
1. Did a physical change occur at any time during this experiment?______

What evidence do you have of that? ______

2. Did a chemical change occur at any time during this experiment? _____

What evidence do you have of that? ______

3. Explain why the mass of the closed bottle was the same before and after the reaction took place. ______

4. Explain why the mass of the open bottle was less after the reaction took place. ______
5. During a chemical reaction, does the total amount of mass change? ______

What law can be used to explain you answer? ______


6. The chemical formula for this reaction is:

____NaHCO3 + ____H3C6H5O7 -----> ___CO2 + ___H2O + ___Na3C6H5O7

List the different elements and the number of atoms of each.

Reactants Products

Challenge: Balance the equation