Missing_Mass_Training

MissingMass_implementation_RESEED_edition

MissingMass_Handout

 

Experiment:

Given a 400 ml beaker, 250 ml cylinder, about a teaspoon of baking soda and a supply of common vinegar, measure how much vinegar is required to completely exhaust the baking soda by adding a little at a time until no more gas is released. Measure the mass of the materials consumed and the resulting product. A workable procedure is outlined below.

  1. Obtain a 400 ml beaker. Weigh it and record its empty weight.
  2. Add about a teaspoon of baking soda. Weigh the beaker with the soda. Record the data and compute the amount of baking soda available.
  3. Obtain a 250 ml cylinder. Weigh it and record its empty weight.
  4. Add about 200 ml of vinegar. Weigh the cylinder with the vinegar.
  5. Add a small amount of vinegar to the baking soda in the beaker. Watch what happens. Continue to add vinegar to the beaker a little bit (less than 5 ml) at a time. Gently stir the mixture and determine if anything occurs. Continue adding small amounts of vinegar until nothing is observed. (If you run out of vinegar, repeat step 4 taking only 100 ml this time.)
  6. Weigh the cylinder with the remaining vinegar. Record the data and determine the amount of vinegar used.
  7. Weigh the beaker containing the baking soda/ vinegar reaction products. Record the data and determine how much product remains.
  8. Add the weight of baking soda and vinegar used and subtract the weight of remaining product. Is any mass missing? If so, where did it go?
  9. Compute the ratio of the missing mass to the mass of baking soda. Record it. Compare it to the ratio obtained by other tables in your class.

 

The missing mass is that of the carbon dioxide released to the room as the bubbles are formed. Some of the CO2 remains in solution, so the calculation will not be exact. In a perfect world, the ratio of the missing mass to the available baking soda should be 44/84 = 0.52. This is the ratio of the molecular weights of carbon dioxide and baking soda computed in the initial steps.
Note that all the students should obtain about this result even if their titration is poorly done and they added far too much vinegar.
To limit the amount of vinegar needed, we must limit the amount of baking soda used. That means that the accuracy of the scale may limit the achievable success in accurately determining the ratio. If the scale does not measure to at least 0.1g, do not expect too much accuracy at these levels.