# 11 Oct. Science 8 Moon today; Experiments in a bottle–closed system

See the moon this morning at 5:40 am viewed from 2nd floor balcony. Notice in the shot with the building how high the moon is in the sky. To take the picture I was turned west and a little south. To get the building exposed in the picture, the moon became over-exposed. Notice the surface in the zoomed picture. Compare to previous pictures on the blog. Also notice that the “curved” portion of the illuminated disk points east–in a line across the sky overhead (towards the sun).

We will go outside for the first period to see this moon and to locate the sun at the same time. Remember this is a key to figuring out the motion–point to the moon and the sun at the same time. Watch how this angle between your arms changes from day to day and how the phases correspond to these angles.

***WHENEVER THERE IS A SET OF DATA, A FIRST STEP IN ANALYSIS IS TO MAKE A HISTOGRAM. THE HISTOGRAM VISUALLY DISPLAYS CENTRAL TENDENCIES (MEAN, MEDIAN, MODE) AND THE PRECISION (HOW VARIED THE RESULTS ARE). WHAT QUESTIONS COULD YOU ASK ABOUT EACH REACTION ABOVE AND BELOW? WHAT TRENDS, IF ANY, ARE SUGGESTED BY THE CLASS DATA? HOW COULD YOU INCREASE YOUR CONFIDENCE THAT A REAL PATTERN OCCURS? WHAT DO YOU THINK THE DIFFERENCE(S) IS (ARE) IN REACTIONS THAT TAKE PLACE IN OPEN SYSTEMS AND IN CLOSED SYSTEMS?***

Finish setting up reactions 4 and 5 (both in closed containers).

Reaction 4.

Place a bit of the steel wool (that has had the coating of oil removed by soaking in vinegar) into a plastic drink bottle with a few drops of water. Close the lid tightly. Dry the outside of the bottle completely. Write your names, period, date, time, and steel wool in moist air on a piece of masking tape and place on the outside of the bottle. Find and record the mass of the bottle.

Reaction 5.

Place a bit of steel wool into a bottle. Ask Dr. F how much. Cover the steel wool with vinegar. Tighten the lid. Dry the outside of the bottle. Label with tape–names, period, date, time, and steel wool immersed in vinegar. Find and record the mass of the bottle.

Look at the bottles with the steel wool in moist air (crushed) left and the steel wool immersed in vinegar (expanded) right. What do you think has happened in each?

Vinegar and baking soda. How can we get the reaction to occur in a closed system so that no gas escapes?

Examine the procedure below. There will also be a demonstration in class of the procedure–be sure to watch. Then try for yourself. Enter your data: https://docs.google.com/a/aes.ac.in/spreadsheets/d/18kjFLcw_LY_ojK5RFEh7sfCikb6U28rCPlQ6Gj0h50A/edit?usp=sharing

What do you already know or think you know about the reaction between vinegar and baking soda? What do you think happens?

1. Wear eye protection.
2. Plastic bottle with tight-fitting lid. Totally clean and dry on the outside. Carefully find the mass of the bottle.
3. Add 50 ml vinegar to the bottle. Find the mass again.
4. Weigh 5 grams of baking soda on a tissue.
5. Gently bring the corners of the tissue together and make a small bundle.
6. Carefully put the bundle into the bottle. DO NOT LET the vinegar come in contact with the baking soda. They must remain separated.
7. Fit the cap so that the corners of the tissue bundle are held when the cap is tightlyclosed.
8. Find the mass of the closed bottle, tissue, baking soda, vinegar.
9. Gentle shake or turn the bottle so that the vinegar comes into contact with the tissue bundle of baking soda. Observe what happens.
10. When the reaction seems to slow / stop, find the mass of the bottle (still closed tightly) again.
11. Very slowly and carefully open the lid. Try not to let droplets of liquid fly out. After the gas is released. Find the mass of the bottle, lid, remaining liquid and tissue. Carefully smell the remaining contents. Compare to the smell of “fresh” vinegar.
13. Clean up the bottle. (No tissue down the sink!)
• What do you think happened to the vinegar?
• What do you think happened to the baking soda?
• What do you think the gas might be?
• Where do you think the gas came from–the vinegar, the baking soda, both?
• How could you find out by experimentation?
• Based on your previous experiments what mass of gas can be released from 2 grams of baking soda and 60 ml of vinegar? Think of a workable procedure.
• What volume of gas can be released from 1 gram of baking soda and 30 ml of vinegar? Think of a workable procedure.
• What are the properties of the gas? Think of a workable procedure to collect and test the gas.
• What proportions of vinegar and baking soda are needed for a complete reaction–where no baking soda is left over and no vinegar is left over? What are the tests to know if you have reached a complete reaction? Think of a workable procedure.
• What remains in the solution after the reaction is completed? Think of a workable procedure.
• Other questions–pose some.
• SOME NOTES ON THE VINEGAR AND BAKING SODA REACTION
• Ingredients before the reaction (reactants)
• Baking soda (Sodium Hydrogen Carbonate) + Vinegar (5% acetic acid in water) —>
• Some products that are not Baking soda and vinegar
• What are these products?
• A gas–what might the gas be? what are its properties? How much gas is produced?? How much volume? Is the gas made from the baking soda only, from the vinegar only, or does each compound contribute something that then comes together to make the gas?
• A liquid (water? something dissolved in the water? more than one thing dissolved in the water?
• What are the relative amounts of baking soda and vinegar that will completely react with each other so that no baking soda is left AND no vinegar is left.

The simplest set of changes to get from vinegar and baking soda to the reaction products.

NaHCO3 + CH3COOH —-> CO2 + H2O + CH3COONa
(this is a description of the overall reaction which occurs in several steps)

Model of reaction between vinegar and baking soda (acetic acid and sodium hydrogen carbonate). Observe, replicate, sketch, photograph, animate.

A.

B.

C.

There is a very interesting project from MIT which uses LEGOS to represent atoms and molecules. Take a look: http://mindandhand.mit.edu/educators/educators.shtml

Student and molecular models

http://fox4kc.com/2012/01/11/little-girl-has-big-breakthrough-in-tiny-world/