# 31 August Science 8 Finish saturated solutions of sugar and salt; Find densities of those solutions; Start crystal growth

1. Saturate 100 ml of water with table salt. Keep track of the amount of salt you add. When you have reached saturation pour off 50 ml of solution and find the mass of that 50 ml sample. Calculate the density. Enter your data in the class spreadsheet.
3. Pour some of the saturated solution in a labeled petri dish (name, period, substance, date, time). Set the petri dish in the tray at the back of the room.
4. Perform the same operations with sugar. (However we will not keep any of the solution to evaporate)
5. Make saturated solutions with 5o ml of hot water and magnesium sulfate, aluminum potassium sulfate, and copper sulfate. Put each solution (separately) into its own labeled petri dish and set aside for evaporation.
6. You now have 4 different substances dissolved in water to saturation and the solutions left to evaporate. This is a technique for “growing crystals.” Make and record initial observations. Take pictures and label them.
7. How do you think density of liquids (both pure substances and solutions) can be explained? Draw sketches of your ideas.
8. How do you think saturation can be explained?
9. Be sure to find out relevant information about the different substances we have used.
10. Reflect on the major challenge of our unit: How can we explain the behavior of matter at the scale we can see in terms of the behavior and properties of basic particles–atoms and molecules that we cannot see. What argument and evidence support the explanation?

In the next class, we will look at a chemical reaction where the product comes out of solution as a crystal. We will observe this reaction under the microscope. The technique involves adding a drop of silver nitrate solution to a piece of copper metal and on another slide a piece of zinc. The copper goes into solution and bonds with the nitrate part of the molecule. The silver comes out in beautiful tree-like crystals. A similar process occurs with the zinc.

We will also examine Brownian motion of fat globules in milk. See what you can find out about Brownian motion. The technique will be described in class.

See the videos showing Brownian motion of fat globules in milk. Apologies for the camera motion. The videos would have been better with a fixed camera. Nevertheless, it is possible to see the random movement of the fat globules. How is this movement interpreted in light of the atomic/molecular theory of matter? (Note: a microscopic fat globule is composed of a truly enormous number of too-small-to-see molecules–according to the theory.)

Video 2

Relate observations to the atomic theory of matter (also called the molecular theory of matter or the kinetic-molecular theory of matter).

Consider these big questions (KEEP IN VIEW-KIV QUESTIONS AND IDEAS):

• What can we observe about the structure and behavior of matter?
• How can we explain what we observe (at the scale of our senses) by structures, entities, and behaviors at a scale we cannot see?
• How can such explanations be tested?
###### THEORY

Be sure to examine the following references:

Extensions for our study of matter–The Periodic Table

See the following videos–express your ideas and questions.

http://ed.ted.com/lessons/the-genius-of-mendeleev-s-periodic-table-lou-serico

Hunting the Elements

https://youtu.be/TDY59XoFSQI

World within World from the Ascent of Man by Jacob Bronowski

http://www.dailymotion.com/video/x20o2dw_bbc-ascent-of-man-10-world-within-world_tv

Elements and the economy:http://www.bbc.co.uk/programmes/p01rcrn6/episodes/guide