# 23 August Science 8 How big is a particle? Finding a limit by dissolving KMnO4 and diluting.

Evacuation drill tomorrow at 1:30. Leave building by specified routes. Meet your advisory on MS field on designated spots.

2:00 in groups of four:

 Aguilar, Esteban-Valentin Al Siyaby, Fareed Khamis Khaleefa Chadha, Anya Choi, Ho Seung Dhar, Arjun Sun Fernando, Maya Hawkins, Keterina Holland, Amya Jeikal, JeongHun Kapur, Vedaa Lee, HyunMin Markwell, Beatrice Norberg, Will Bridger Rubin, Esther Delaney Saigal, Keshav Sikka, Uvanka Soni, Tanush Stawirej, Natasza Elzbieta Takizawa, Ronan

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

Today we will conduct the activity of dissolving a crystal of potassium permanganate and then diluting the solution until the color just disappears. The purpose of this activity is to help us contemplate the size of particles–atoms and combinations of atoms called molecules. See previous blogpost: http://rfrazier.msblogs.aes.ac.in/2017/08/19/21-august-science-8-what-is-a-flame-5-elements-and-their-haikus-and-evidence-for-the-existence-of-atoms/

A big challenge in studying matter is to link the behavior of matter that you can observe at a macroscopic scale to inferred behavior of atoms and molecules at a scale we cannot see.

Find mass and volume of a crystal.

• Put the crystal of potassium permanganate in a test tube. Add 1 cm of water. Dissolve the crystal completely by shaking vigorously with your thumb over the end of the test tube. Then add water to a total volume of 10 cm. This is a ‘10 times’ dilution. Pour this 10 cmof purple solution into a 100 cmbeaker and then fill up the beaker with water. This is now ‘100 times’ dilution. Fill the 10 cmtest tube with this solution and throw the rest away. Dilute this again in the beaker to 100 cm. It is now a ‘1000 times’ dilution.
• How many times can the solution be diluted by a factor of 10 before the color is so pale that it is just visible?
•  *The final dilution factor indicates that if matter is made of small particles, that these particles must be very, very small.
• FYI–Potassium permanganate has the chemical formula: KMnO4–this means there is one atom of potassium (K), one atom of Manganese (Mn), and 4 atoms of Oxygen (O) in one molecule.

Points of reflection–for your digital science notebook entry:

• What do you think happens when something dissolves?
• Examine and react to the following sketch:
• When you reach the final dilution, what inference can you make about the “size” of a particle of the substance? (It is much much smaller than you can imagine.)
• Why would more of one substance dissolve in a certain amount of water than another substance? Why would there be differences in solubility?
• What differences do you think there are between dissolving and melting?
• How do you imagine that light interacts with matter? What makes the crystal and solutions purple?
• How do you think light interacts with your eye?
• What are your own questions and ideas?
• Be prepared to share with the class.

There is much information about matter and about the scientific explanations of matter–books, videos, webites, etc. Such sources make many claims. The videos below contain many examples of claims. Ask yourself, how did people find these things out? What evidence led them to such inferences and conclusions?

Review references from the previous blog–especially evidence for the existence of atoms. Bring your questions forward to the class for discussion. http://rfrazier.msblogs.aes.ac.in/2017/08/19/21-august-science-8-what-is-a-flame-5-elements-and-their-haikus-and-evidence-for-the-existence-of-atoms/

What are some of your ideas about the following? You may look at them. We will discuss in class at some point:

How did scientists find out about

1. the existence of atoms/molecules?
2. the size of atoms/molecules?
3. the structure of atoms/molecules?
4. the behavior of atoms / molecules?

Can you identify the evidence and follow the argument?

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