The Law of Conservation of Mass

INTRODUCTION:

The Law of Conservation of Mass states that matter is neither created nor destroyed during a chemical reaction and that the mass of a system should therefore remain constant during any chemical process. This means that during any reaction the sum of the masses of the products of a reaction must be the same as the sum of the masses of the reactants. For example, imagine using a spark to ignite a match in a glass jar which is so tightly sealed that no matter can enter or escape. As the match burns, flammable substances from the match and some oxygen from the air are transformed into water, carbon dioxide, and other substances. Measurements taken before and after the match burned would show that the total mass remains the same.

Although this concept may seem obvious, it was not always so.

When early scientists first began exploring chemical changes, they frequently did not consider the effects of the air and other gases. Similarly, the equipment originally used often did not take into account the possibility that a gas could be a product or a reactant.


PURPOSE:

In this experiment you will:
  • Demonstrate proficiency in detecting a chemical reaction.
  • Measure masses of reactants and products with a laboratory balance.
  • Relate observations of a chemical reaction to the Law of Conservation of Mass.


EQUIPMENT:

100 mL graduated cylinder
250 mL beaker
250 mL flask
Plastic bottle with cap
Rubber balloon (2)
Baking soda
Vinegar
Effervescent tablet
Electronic Balance
Small square of coffee filter



INSTRUCTIONS:

  1. Each person in your lab group must read every page in this online procedure. Along the way, there will be questions that you must answer.
  2. Designate one person in your group as the Data Recorder. This person should open the Google document Experiment 6 - Conservation of Mass for the approved answer template.
  3. When this Google document opens, sign in to your Google account.
  4. From the FILE Menu, choose Make a copy...
  5. From the FILE Menu, choose Rename...and rename the document as follows: Exp 6 - Period (1, 3, 6, or 8) - Group #.
  6. Share this document with the members of your group and with Mr. Skubis at HSTChemistry@gmail.com.
  7. As a group, answer all questions. Remember to use complete sentences and be mindful of grammar, spelling, and punctuation.
  8. REMEMBER: **Plagiarism** is a form of **Academic Dishonesty** which carries harsh consequences. DO YOUR OWN WORK!


PROCEDURE:

Using the data tables on the accompanying handout, RECORD OBSERVATIONS and/or DATA for each procedure step.

Part A: Baking Soda and Vinegar - Open System

  1. Pour about 50 mL of vinegar into the 250-mL beaker. Place small scoop of baking soda onto the tissue square and fold the contents into a neat little packet. Place the beaker of vinegar and the packet of baking soda on the laboratory balance and record the total mass of these reactants and containers.
  2. Carefully place the packet into the beaker and allow the chemical change (fizzing and bubbling) to fully react. To be sure it is completed, carefully swirl the chemicals and observe. Measure and record the total mass of the products and containers using the same balance you used before.

Part B: Baking Soda and Vinegar - Closed System

  1. Pour about 50 mL of vinegar into the plastic bottle using the funnel (to avoid getting the neck of the container wet). Prepare another packet of baking soda/tissue as in Step 1 above, and measure and record the total mass of these reactants, bottle, and cap.
  2. Tilt the bottle (as much as possible without spilling the contents), insert the packet of baking soda into its neck (being careful not to wet it), and tightly secure the cap. Tip the bottle upright and allow the contents to fully react. Measure and record the total mass of the products and containers. Remove the cap and observe what occurs.

Part C: Baking Soda and Vinegar - Closed System

  1. Pour about 50 mL of vinegar into the 250-mL flask using the funnel to make certain the neck of the flask does not get wet. This time, scoop the baking soda directly into the balloon as one classmate holds the balloon open. Measure and record the total mass of the reactants, flask, and balloon.
  2. Slip the open end of the balloon over the mouth of the flask making sure that the “bulb” of the balloon remains downward so contents do not spill out and making sure the mouth of the flask is “sealed” with the balloon. Tilt the balloon up to allow the baking soda to fall into the flask allowing the reaction to fully react.
  3. Measure and record the total mass of the products, flask, and balloon. Remove the balloon and observe what occurs.

Part D: Water and Effervescent Tablet - Open System

  1. Thoroughly clean the flask & fill with 50 mL of water.
  2. Obtain an effervescent tablet and carefully break it in half.
  3. Place the flask & half of an effervescent tablet on the balance & record the starting mass.
  4. Place the tablet into the flask of water. Swirl & wait 3 minutes.
  5. Once the reaction is complete, record the ending mass.
  6. Calculate the amount of mass changed.

Part E: Water and Effervescent Tablet - Closed System

  1. Thoroughly clean the flask & fill with 50 mL of water.
  2. Place half of an effervescent tablet into a balloon.
  3. Place the balloon around the rim of the flask, but do not let the tablet fall into the water.
  4. Find & record the starting mass of the flask & balloon with tablet.
  5. Lift the balloon, causing the tablet to fall into the water. Swirl & wait 3 minutes.
  6. Once the reaction is complete, record the ending mass.
  7. Calculate the amount of mass changed.

Disposal

  1. Baking soda packets and rubber balloons can be disposed of in the garbage.
  2. Vinegar can be disposed down the sink.
  3. Effervescent solutions can also be disposed down the sink.
  4. Clean all glassware and return to the proper place.
  5. Clean all work surfaces and personal protective equipment as directed by your instructor.
  6. Wash your hands thoroughly before leaving the laboratory.


ANALYSIS

In this activity you will measure the mass of your system both before and after mixing. This will allow you to investigate the Law of Conservation of Mass.

Use the tables in the approved handout to organize your observations and data described in the procedure. In the Analysis column, record your interpretation of what happened in each step.

FOLLOW UP QUESTIONS

Write answers for the questions. Remember to use whole sentences. Pay close attention to grammar, spelling, and punctuation.