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Archive for the ‘Chemistry’ Category

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Interactive Practice with stoichiometry problems:

“That which you persist in doing becomes easy to do – not that the nature of the thing has changed, but your power and ability to do has increased.” — H.J. Grant

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Goal: Be able to use the law of conservation of mass to write balanced chemical equations, identify the basic types of chemical reactions, and predict the possible products from a given set of reactants.

You must demonstrate your achievement of this goal.  In a blog post, (1) explain how to balance an equation and why it is important, and (2) describe different labs you did, what type of reaction it was, and provide a balanced reaction for each.  You have done synthesis, decomposition, single-replacement, and double-displacement labs.

You must also (3) describe how to predict the possible products that will occur from a given set of reactants, and (4) demonstrate your ability to predict reaction products.

As of the first week of March, chemistry students have conducted the below list of chemistry labs. Use this list to support your evidence of attainment of the above goal.

  1. Baking Soda to Salt Lab
  2. Limiting Reactants Lab
  3. Chemical Reactions Webquest
  4. Three Types of Chemical Reactions
  5. Reactivity of Metals
  6. Hydrate Lab
  7. Molecules of Candle Burned
  8. Molecules of Chalk In Your Name
  9. Covalent or Ionic Bonding Lab
  10. Halides Lab
  11. Periodic Trends
  12. Ionic vs Covalent
  13. Half life of Candium
  14. Isotopes of Vegium Lab
  15. Rutherford Lab
  16. Law of Conservation of Mass
  17. The quality of Laboratory Measurements
  18. Measuring Stuff: Tools and Skills
  19. Density Problems
  20. Lab Skills Lab
  21. Observations Lab

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This past month chemistry students have been learning how to convert between grams, molecules, and moles, so each day the bell-ringer/do-now/QOD assignment was a calculation of molecules of something familiar: chalk, candle wax burned, nicotine, aluminum foil, etc. I believe that each day’s practice helped solidify their understanding of the concept. So one day I asked how many molecules in a snow flake. Since we had to start with a mass, and I did not have time to determine the mass of a single snowflake, I turned to the internet and found Archimedes Notebook: How much does a snowflake weigh?  Thus, I gave the students the following information

Most snowflakes weigh from 0.001 to 0.003 grams, with a heavy snowflake coming in at 0.02 grams. Choose a mass within that range and calculate the number of molecules of water in the snowflake.

Thus, different students came up with different numbers of molecules, giving us a range of data.  Note:

The largest snowflake ever seen was 8 by 12 inches and was reported to have fallen in Bratsk, Siberia in 1971.

Most students elected to use the average of the lower two numbers, and calculated as follows:

mol snowflake

That is a lot of molecules. Adding or subtracting just one molecule of water would result in a unique snowflake. And considering that water is a polar molecule, the hydrogen bonding arrangement possibilities is mind boggling.

Then we have to consider factors that affect how a snowflake develops. NOAA gives this simplified explanation, which still is not the entire story:

A snowflake begins to form when an extremely cold water droplet freezes onto a pollen or dust particle in the sky. This creates an ice crystal. As the ice crystal falls to the ground, water vapor freezes onto the primary crystal, building new crystals – the six arms of the snowflake.

…The intricate shape of a single arm of the snowflake is determined by the atmospheric conditions experienced by entire ice crystal as it falls. A crystal might begin to grow arms in one manner, and then minutes or even seconds later, slight changes in the surrounding temperature or humidity causes the crystal to grow in another way.  ~ NOAA

From snowcrystals.com we get a bit more information:

Snowflake Morphology

Snowflake Morphology

We see that thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).  Furthermore, we see from the diagram that snow crystals tend to form simpler shapes when the humidity (supersaturation) is low, while more complex shapes at higher humidities. The most extreme shapes — long needles around -5 C and large, thin plates around -15 C — form when the humidity is especially high.

PBS tried to get a definitive answer to this question “So is it really true that no two snowflakes are alike?” from physicists Kenneth Libbrecht, a physics professor at the California Institute of Technology and avid snowflake photographer, and John Hallett, director of the Ice Physics Laboratory at the Desert Research Institute in Reno, Nev., and got the following response:

“It’s like shuffling a deck and getting the exact same shuffle for 52 cards,” Libbrecht said. “You could shuffle every second for the entire life of the universe, and you wouldn’t come close to getting two of the same.”

So, there you have it. While not impossible, it is highly unlikely given that there are a trillion, trillion, trillion (a 1 with 36 zeros!) different types of snowflakes.

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How Many Molecules of Chalk?

A Chemistry “Do Now”

Mole map

How much chalk does it take to write your name?

Figure this out!

Step 1. Mass a piece of chalk.

Step 2. Use this chalk to write your name on the board.

Step 3. Remass the chalk.

Step 4. Convert grams to moles, using the grams of chalk used.

Hint: Chalk is calcium carbonate, CaCO3

Step 5. Convert moles to molecules.

Step 6. Write and communicate everything you did and discovered in a visual.

moles_too_many

Click on the image!

 

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Strontium is chemically similar to calcium (note where it appears on the periodic table). If you lived in a city where there had been a nuclear accident, you and your family might be exposed to strontium-90, which is the principal health hazard in radioactive fallout because it can easily get into the water supply or milk and then be ingested by people.Strontium-90, which is a pure β-emitter, has a half-life of 28 years. This in turn gives rise to yttrium-90, which has a half-life of 64 hours and is a β-emitter in its own right, and the process finally leads to the stable zirconium-90.

Write about how the strontium-90 might accumulate in your body (teeth and bones) and how it might affect you. Include your ideas about how its half-life of 28.8 years would be important. Suggest ways that government agencies, such as your state’s department of health, might test for strontium-90. Where in your environment might scientists look for large concentrations of strontium?

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The Rutherford Lab illustrated how models are used to understand atomic theory and the difficulties Rutherford faced. Use your inductive and deductive reasoning to interpret atomic theory information relayed through the textbook, lectures, and labs, and draw conclusions about how to understand atomic theory based on your best analysis. Synthesize and make connections between “information” and the use of models. This post must be 200 words in length and include an illustration.

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Using 21st Century Tools

“It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is the most adaptable to change.” ~ Charles Darwin

Students are blogging for their portfolio in chemistry class:

~ Gwen   ~   David   ~    Olivia   ~   Jess   ~   Skylar    ~   Corey   ~   Sam   ~   Cody   ~   Kassidy   ~   Nicolette   ~   Ben   ~   Krystal   ~   Lauren   ~   Mike   ~   Caitlin   ~   Blaine   ~   Molly   ~   Mariah   ~   Maddie   ~   Devan   ~   Elise   ~   Kade   ~   Rachel D.   ~   Isabella   ~   Alena   ~   Cam   ~   Haley   ~   LeeAnne   ~   Taressa   ~   Joe   ~   Dakota   ~   Madison   ~   Alex   ~   Kevin   ~   Devin   ~   Caroline   ~   Hannah   ~   Michaela   ~   June   ~   Megan   ~   Rachel S   ~   

To see why, read Using A Blog As A Portfolio.

Hard portfolio                                       

Technology… is a queer thing. It brings you great gifts with one hand, and it stabs you in the back with the other.  ~C.P. SNOW, New York Times, 15 March 1971.

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