12 October Science 8 Chemical reactions continued

Today / Tonight view the moon.

Here is the data:

The moon rises in the eastern part of the horizon this afternoon at 15:21. It will cross the north-south line in the sky, called the local meridian, at 21:08. It will set tomorrow morning at 3:00. The illuminated part of the moon is getting larger and brighter. It rises later each day, crosses the meridian later each day, and sets later each day (be sure to observe this in addition to seeing the times on the linked chart below). The moon will be full on the 16th. It rises at sunset, sets at sunrise, and crosses the meridian close to midnight. Why would this be?

Begin keeping a moon journal. Make a sub-folder in  your astronomy folder. For each observation:

  1. date
  2. time
  3. location (describe as precisely as you can
  4. direction you are looking along the horizon (bearing or azimuth)
  5. angle of elevation above the horizon
  6. appearance–phase, orientation (photo if you have a good camera, sketch; if you have binoculars, look at the moon and notice the appearance of the surface; it is very interesting to look right at the edge of the illuminated portion; what do you see?)


Today we will carry out the vinegar and baking soda reaction in a closed bottle.

You should have some idea about the results. Be sure to write down your expectations.

Enter your data on the class spreadsheet:


Use 4 grams of baking soda and 50 grams of vinegar. (See the amount of gas evolved in the open bottle experiment from a previous class.)

See the following photos and observe the demonstration in class. This experiment demands careful technique. Listen to the details. Ask questions.









The vinegar has been poured into the bottle. The baking soda is wrapped loosely in a bundle of tissue (not paper towel). A corner of the tissue is held by the tightly closed cap so that the bundle is NOT in contact with the vinegar. It is VERY IMPORTANT that the tissue does NOT extend outside the cap. If the tissue does extend outside the cap, your system will not be completely closed and both gas and liquid can escape. When you have set up the bottle properly, you can find the mass of the entire system. Compare this technique to the box of changes we saw in the Ring of Truth video segment on the Conservation of Mass during last class.









In this picture the bottle has been tilted so that the vinegar wets the paper while the bottle remains tightly closed. Compare the scale reading in both pictures.









In this picture, the cap has been loosened and then removed after the gas escapes. It is important that only gas leaves the bottle. Small drops of liquid that escape will make the loss of mass look larger than the mass of the escaped gas.

Vinegar is 5% acetic acid in 95% water. Acetic acid = CH3COOH. The chemical name of baking soda is sodium hydrogen carbonate. The formula of baking soda = NaHCO₃. What do you think the products of the reaction are? Why? What do you think the gas is? What is the source of the gas–the acetic acid, the baking soda, or both? What is your reasoning? What would molecular models of the reactants look like?

*  * * * * * * * * *

You may take apart the bottles from the previous experiments.

  1. Do not discard any of the non-liquid materials in the sink. Use the dust bin. Remove tape labels from bottles and rinse bottles.
  2. If you want to test the gases, check with Dr. F, after you have everything set up. One basin for 2 groups. One gas tested at a time. Everyone has safety glasses. You need to be able to describe the procedure step by step to Dr. F.
  3. Classroom must be clean and straight 5 minutes before dismissal time.

Be sure to have a complete digital science notebook entry for today.

  1. Regular notes.
  2. What we did (do not need to describe clean-up, just the experimental procedures conducted)
  3. What you saw. All results, data, observations.
  4. What you talked about–introduction, closing, conversations with partner about the experiment, conversations with Dr.F.
  5. What you think, wonder, expect? Your reflections.
  6. Photos of important aspects of the class.
  7. Sketch–not necessarily of objects. Could be of ideas. (Perhaps your first imagined structures of the acetic acid, baking soda, gas, other product(s) molecules.)

Homework due in DSN next class:


What does the author mean, “we all practice chemistry without being aware of it?” Please include specific examples to support your answer. Refer to a paper from the beginning of our unit Fundamental Questions about Matter.

What part did craft knowledge play in the development of chemistry, according to the author? Use specific examples.

What were the dreams of “alchemy?”

What are some of the “ironies” in the history of chemistry? Look at the stories of various substances to see where they started and the surprising place they ended.

What is meant by “tapirage?” Why is this example included in the article?

What is the role of the balloon in the development of chemistry? What is significant about a balloon in studying matter?

How did ideas about elements change from those of the ancient Greeks to those of scientists who followed Mendeleev?

Pick one of the pictures and write a detailed analysis of it.


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