Law of Conservation of Mass Lab

Background: “As matter cycles through the Earth system, the matter can undergo chemical changes that cause it to change state or change physical properties. However, although the matter may change form, it is not destroyed. This principle is known as the law of conservation of mass. In this lab, you will cause two chemicals to react to form products that differ from the two reacting chemicals. Then you will determine whether the amount of mass in the system (the experiment) has changed.” (DeGaetano & Pasachoff, 2008 p. 48)

The word equation for the following reaction is as follows: vinegar + baking soda  sodium acetate + water + carbon dioxide The chemical equation for the reaction is: CH3COOH + NaHCO3 NaC2H3O2 + H2O + CO2

Purpose: To attempt to verify & observe the Law of Conservation of Mass - In any chemical reaction, the total mass of the reactants is always equal to the mass of the products.

Materials:  balance  large plastic cup  400 mL beaker  graduated cylinder  weighing paper/boat  ~4 g baking soda  plastic sandwich bag, twist tie  ~50 mL vinegar

Procedure:

Trial #1 1. Using the triple beam balance, weigh 4g of baking soda using weigh boat. 2. Using a graduated cylinder, measure 40 mL of vinegar. Pour vinegar into beaker. 3. Place the cup/vinegar and the weigh boat/baking soda on the pan of the laboratory balance. Measure and record (to the nearest 0.01g) the mass of these reactants plus containers. Record in the first row of your table under “Initial Mass”. 4. Carefully pour the baking soda into the cup of vinegar and allow the reaction (fizzing and bubbling) to complete. 5. Measure and record the mass of the remaining products including containers (to the nearest 0.01g). Record in the first row of your table under “Final Mass”

Trial #2 5. Repeat step 1, measure out 4g of baking soda. 6. Carefully transfer the baking soda to one corner of the plastic bag and seal with a twist tie. 7. Using a graduated cylinder, measure 40 mL of vinegar. Pour the vinegar in the upper part of the bag and seal the bag. 8. Place the bag in a beaker and measure the mass of the beaker, bag and reactants. Record in the first row of Table 2 under “Initial Mass” 9. Remove the twist tie from the bag and mix the reactants. 10. When the reaction has finished, place the bag and beaker and twist tie back on the balance and measure the mass. Record the “final mass” in the first row of Table 2.

11. Gather the “change in mass” for trial #1 and trial #2 from 5 other groups and record in rows 2-6 of Table 1 and Table 2 13. Clean up all lab equipment, wash glassware and dispose of chemicals according to your teacher’s instructions.

Safety Precautions:

Independent variable:______

Dependent variable: ______

Your Hypothesis: ______

______

Results:

Data for Trial 1: Baking soda and vinegar reaction in cup Group Initial mass (g) Final mass (g) Change in mass (g) My Group Data XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX Average Percent error

Data for Trial 2: Baking soda and vinegar reaction in bag Group Initial mass (g) Final mass (g) Change in mass (g) My Group Data XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX XXXX Average Percent error

1. Fine the change in mass = Initial mass – Final mass 2. Find the average change in mass for all six groups 3. Find the percent error (p. 13) of change in mass for your data: Calculation: (average – your value/average) * 100 = percentage error Inquiry/Analysis Questions: (Type your answers, 12pt type, double spaced)

1. What evidence was there that a chemical reaction occurred? 2. Compare the change in mass that you calculated for the first trial with the change in mass you calculated for the second trial. 3. Was the law of conservation of mass violated in the first trial? Explain your answer. 4. What evidence of the conservation of mass does the second trial show? 5. Indicate the state of matter for each reactant and product. 6. Was the first trial an example of a closed system or an open system? Which type of system was the second trial? Explain your answer. 7. What was your percent error? Was error a problem in this experiment? Identify at least 2 sources of error that may have affected your data. 8. How else could you have tested the law of conservation of matter for this reaction? What other experimental designs could you have implemented? Explain your revised procedure.