Aleksza/RuscherChemistry2013-14

Law of Conservation of Mass

(Adapted from Dr. Wilhelm)

Objective: To design an experiment that will prove the law of conservation of mass.

Background: 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 a 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 masses of the reactants.

In this experiment, you will determine whether mass is conserved by examining a simple chemical reaction and comparing the mass of the system before the reaction with the mass after the reaction.

Safety Requirements: Safety goggles are required for this lab.

Materials:

Weighing boat/paper

Electronic balance

50 mL graduated cylinder

2 plastic cups

Glass stirring rod

Quart size Ziploc bag

Rubber band

Sodium Bicarbonate (baking soda)

5% Acetic Acid solution (vinegar)scoopula/spatula

Preparation:

Day One:

  • Design a plan to execute part II of this lab. You will need to develop a clever way to contain yet separate your reactants and products in a closed system (Ziploc bag).
  • Document your plans as written formal procedures or in a details flow diagram.
  • Plans must be teacher approved!
  • Design and prepare data table*.

* Remember you will need mass measurements of your reactants and mass measurements of your products. Be sure to account for all parts of your system including materials you use to contain your chemicals. Allow for two trials of each experiment in your data table.

Day Two:

  • Conduct lab activities: Part I (open system), Part II (closed system)
  • Repeat each experiment to help validate your data.
  • Clean lab area and dispose of waste.
  • Return to desks and analyze your data.
  • Answer post-lab questions.

Procedure:

Part I (open system)

  1. Using weighing paper/boat and an electronic balance, measure out 2 grams of baking soda.
  1. Transfer all of the baking soda to a plastic cup. Be careful not lose any of the sample
  1. Using the 25 mL graduated cylinder, measure 25 mL of vinegar and transfer into the other plastic.
  1. Place both cups on the electronic balance and record the Initial Mass in your data table. This is the mass of the chemicals and the cups.
  1. Remove cups from the balance and carefully pour the vinegar into the cup containing the baking soda. Add only a small amount of vinegar at a time to avoid a strong reaction that causes splattering and the loss of part of the reactants or products. Stir mixture with the glass rod to ensure the reaction has gone to completion. (No more bubbles.)
  1. When the reaction has finished, place bothcups back on the balance and determine the final mass of the system to the nearest 0.01g.
  1. Record the final mass in you data table.
  1. Calculate the change in mass. (Initial Mass – Final Mass)
  1. Clean and dry your cups and repeat the procedures for a second trial.
  1. Calculate the average change in mass and record it on your data sheet. AVG = (Change in mass for trial 1 + Change in mass for trial 2) / 2

Part II (closed system)YOU DESIGN IT!

  1. *Design a plan to execute part II of this lab. You will need to develop a clever way to contain yet separate your reactants and products in a closed system (Ziploc bag).
  1. Document your plans as written formal procedures or in a details flow diagram. Record on your data sheet
  1. Record your materials on the data sheet
  1. Plans must be teacher approvedPRIOR to conducting the experiment!

* Remember you will need mass measurements of your reactants and mass measurements of your products. Be sure to account for all parts of your system including materials you use to contain your chemicals. Allow for two trials of the experiment.

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Clean-up and Disposal:

  1. Final product can be poured down the sink with running water.
  2. Rinse out glassware and plastic cups. Set them to dry on the drying rack.
  3. Put all other materials back at prep station and wipe down work area with a wet paper towel. Be sure to wash your hands before returning to your desk.
    NAME:______MOD:______

LAB PARNERS:______

DATE (S) OF EXPERIEMENT:______

LAW OF CONSERVATION OF MASS DATA SHEETS

QUESTION:______

HYPOTHESIS:______

Part 1 Data:Open System

TRIAL 1 / TRIAL 2
Mass of baking soda and vinegar BEFORE REACTION / grams
Mass of baking soda and vinegar AFTER REACTION / grams
Change in mass / grams (mass before - mass after)
Average Change in Mass / Avg = (change 1 + change 2) / 2

RECORD YOUR OBSERVATIONS DURING THIS EXPERIMENT:______

Part 2 Data: Closed System

List of Materials:

List Procedures:

TEACHER APPROVAL:______

TRIAL 1 / TRIAL 2
Mass of baking soda and vinegar BEFORE REACTION / grams
Mass of baking soda and vinegar AFTER REACTION / grams
Change in mass / grams (mass before - mass after)
Average Change in Mass / Avg = (change 1 + change 2) / 2

RECORD YOUR OBSERVATIONS DURING THIS EXPERIMENT:______

Post-Lab Questions

  1. List/Note all evidence indicating that a chemical change occurred in this experiment.
  1. The reaction that takes place in this lab can be summarized as follows:

NaHCO3(s) + CH3COOH(aq) → NaCH3COO + H2O(l) + CO2(g)

Sodium bicarbonate + Acetic acid yields Sodium acetate + Water + Carbon dioxide.

List the Reactants:

List the Products:

  1. Was the law of conservation of mass violated in Part I of the experiment? Support your answer with observations and data.
  1. Was the law of conservation of mass violated in Part II of this experiment? Support your answer with observations and data.
  1. Compare your results for Part I (open system) and Part II (closed system). Do the observed trends support the Law of Conservation of Mass?
  1. How does comparing the two systems in Part I and Part II help explain the law of conservation of mass?
  1. Explain whether or not your hypothesis was shown to be true.