Density of soap and week one in physical science

Day one was a course introduction. Day two opened with an overview of the preassessment results. This chewed up too much time and didn't leave time to have the students make a density calculation. Recommendation is to drop this review in future terms.

Forgotten: 500 ml water bottle. Not forgotten but almost: a kilo of sugar.

Wednesday hear included two 1000 ml Erlenmeyer flasks, a recently acquired 300 ml beaker, Silka papaya soap, ruler  mass balance, and the usual collection of rectangular blocks and cubes. The Silka would prove to a fail.

Silka would come in at 88 grams, 2 grams under the packed mass. The lecture-demonstration followed the usual arc as seen in the board shots below.

With the soap in the 300 ml beaker, water was added up to the 300 ml mark. The soap was sitting on the bottom of the beaker.

Then the soap was removed. Reading the new mark was problematic. With a habit of overestimating volume, the error was pushed high and led to a contrary result. 

With time tight, the systems of measurements unit was truncated.  As were the density calculations.

The Erlenmeyer flask performed stellarly, turning in a density for water of 0.99 grams per cubic centimeter. Which led to floating versus sinking.

The Silka soap was 87 grams post immersion. The displaced water was estimated at 90 cubic centimeters which yielded 0.97 grams per cubic centimeter. Silka is predicted to float but sinks. Error is in the volume. That said, the demonstration demonstrated the importance of accuracy in measurement.

The exercise was fraught with issues. The 300 ml beaker marks were hard to read. And once soapy they were impossible to read. A worthy precursor to the upcoming lab, but perhaps with a larger bar of soap and a larger beaker.

The Erlenmeyer flask at 1000 cubic centimeters.

The left board on Wednesday 

The right board

The failure of the Silka soap.

Early arrival Thursday in the ride that replaced the Nissan during the summer.

Gear 

Strangely clay like yet sticky soap. Dense too. 

128 grams but about the size of a 90 gram bar of soap.

At 8:00 I ran the demonstration using the Silka soap, hoping to measure accurately enough to get the density onto the correct side of one gram per cubic centimeter. Alas, the slope was once again below one.

The board, however, had not been erased so I was able to add in the Wednesday measurement. 

The result was a density just barely above one gram per cubic centimeter. Victory was snatched from the jaws of a double defeat. Still, Silka soap has been a two term jinx, time for a plan B.

The papaya soap proved to be very pliable. AR/SC 131 has been born. 

 

More sculpture but from a more brittle soap.

Artist in residence. The 8:00 section wrapped at 10:30.

 

Dalan pink rose soap was purchased to provide a few spare bars of soap.

At 11:00 I used Dalan pink rose beauty soap from Ace Office Supply for my example.

Although the bar was only obloidally rectangular and required heavy carving on all six faces,  the results were solidly in the dinking camp. 

I cut slabs of 0.5 cm off only, and only from the end of the longest measure.

The only board notes. 

Friday I reworked three problematic lab reports in class (anonymously). I am not sure this actually helped, many clearly paid no attention.