When we consider chemical exposure, it’s important to think about frequency: how often will exposure occur?  Imagine you are at the gas station.  It’s a warm day, and as you fill you fill your tank with gas, you smell the faint scent of gasoline vapor in the air.  As you wrap up and put the nozzle back on the pump, a few drops of gas fall from the nozzle, thus preparing the scene for the next person.  You just experienced an acute inhalation exposure to gasoline vapor.

• Acute: exposure to a chemical for 24 hours or less

Thankfully for you, it is a low-level exposure; you will be fine.  For the attendant who has been working at the gas station for the last few years, every time they tidy up the pumping area (take out the garbage, change out the soapy water for washing windshields, sweep up litter, and spread kitty litter to absorb larger gas spills) they are experiencing chronic exposure to inhaled gasoline vapors.

• Chronic: exposure to a chemical for more than 3 months

When it rains, those drops of gasoline are washed down into the sewers and are carried out into Puget Sound.  Fish swimming in the area come into contact with the gasoline, absorbing it through their eyes and skin and inhaling it through their gills.  The gasoline evaporates when the weather turns sunny again, so the fish are only exposed for a few days (sub-acute exposure).

• Sub-acute: exposure to a chemical for 1 month or less

Birds in the area feed on the gasoline-exposed fish.  It takes a few months for the birds to fully metabolize the gasoline ingested with the fish (sub-chronic exposure).

• Sub-chronic: exposure to a chemical between 1 to 3 months

Your turn to show what you know.  Complete the Types of Exposure Google Form and then return to Weeks 34-35 – How Much Is Too Much? and continue working.

Now that we understand some of the variables involved with evaluating exposure to toxic chemicals, it’s time to move forward with the Toxin Research Project.  The first step is to decide which toxin you want to research.  You are welcome to select anything of interest to you, as long as you can identify a specific molecule in the PubChem (NCBI) database AND you can find an appropriate LD₅₀ for the molecule.

For inspiration, the websites below can help get you started:

• Alcohol (ethyl alcohol – beer, wine)
• Alcohol (mixed with other drugs)
• Arsenic (contaminated water)
• Benzene (gasoline, cigarettes, industrial processes
• Benzodiazepenes (Xanax)
• Caffeine (beverages, chocolate)
• Cocaine
• Copper (industrial processes)
• CBD (marijuana)
• Formaldehyde (smoking, manufacturing)
• Glyphosate (weed killer)
• Iron (vitamins)
• Lead (Flint water crisis)
• LSD (ergot fungus)
• Methamphetamines (meth, MDMA/Ecstasy)
• Monosodium glutamate (food additive)
• Nicotine (vaping and cigarettes)
• Opioids (heroin, Vicodin)
• Oxycodone (OxyContin)
• Psilocybin (magic mushrooms)
• Silver (argyria)
• THC (marijuana)
• Toluene (gasoline)

For this part of your work, you need to create a Google Slides document.  All of your Toxin Research Project work will go into the Google Slides.  Instructions for completing this part of the work:

1. Create a Google Slides document
2. Title the document “Toxin Research Project – Your Name”
   • Example: Toxin Research Project – Pierre Swart
3. Slide 1 must include:
   1. Name of the molecule
   2. A link to the PubChem database entry.
   3. An image of the molecular structure.
   4. How someone might be exposed to the molecule (i.e. a specific food, drink, plant, animal, type of work, a location in the environment where it naturally occurs, etc).
   5. The LD₅₀ for the molecule (including species and route of administration) most relevant to the route and type of exposure you selected.

The molecule name, image, and LD₅₀ for the molecule should all be found in the PubChem database.  If you select a toxin from the list above, the linked article will provide you with information about exposure to the molecule.  If you pick a toxin not on the list, you will need to do that research on your own.

Need help?  You have options:

1. Click here and watch a video of Mr. Swart guiding you through the process of conducting the research to complete Slide 1.  You will also be provided with an example of Slide 1.
2. Attend office hours on Tuesday and/or Thursday
3. Email Mr. Swart with specific and detailed questions.

Finally, I would like to be able to post these online to share with each other.  Please be creative in your layouts and make sure your name is not actually on the slide anywhere.  Your name should only be in the title of the document.  Have fun!

When finished with Slide 1, return to Weeks 34-35 – How Much Is Too Much? and continue working.

Welcome to Weeks 34 and 35!  It is finally time to answer that age-old question: How much is too much? If I had a dollar for every time a student asked me, “Can I eat it?” after watching a chemical reaction in a lab…I could personally fund the Week 34 Bonus Credit Opportunity question (scroll way down to find it!).   We all know the answer is always, “No food or drinks in the lab!”  But why?  This week, you will be able to find out for yourself.  You have two weeks to complete this work.  The recommended weekly work schedule is provided below.  You must complete the weekly attendance check-in, but you are welcome to adjust the learning schedule to meet your own needs.  Also, for anyone working on the Unit 4 Honors Project, this lesson comprises an important section of that project.

Week 34 (recommended)

1. Week 34 Attendance Check-In (required by 10am 5/15)
2. Routes of Exposure (Google Form assignment)
3. Types of Exposure (Google Form assignment)
4. Toxin Research (Google Slide assignment, slide 1)
5. Limiting Reactants Revisited (optional lab report)

Week 35 (recommended)

1. Week 35 Attendance Check-In (required by 10am 5/22)
2. Toxicology (Google Slide assignment, slide 2)
3. Toxin LD₅₀ Calculations (Google Slide assignment, slide 3)
4. Graph of LD₅₀ (Google Slide assignment, slide 4)
5. Toxin Research Project Check-In (Google Form required)

You did it!  Just to make sure, here’s a checklist of items you must complete this week by Sunday, May 24 at 11:59pm:

• Weekly Attendance Check-In (school district requirement)
• Routes of Exposure Google Form (worth +10 assignment points)
• Types of Exposure Google Form (worth +10 assignment points)
• Optional Lab  Report (worth +50 bonus lab report points)
• Slide 1 of Toxin Research Project (worth +10 project points)
• Slide 2 of Toxin Research Project (worth +10 project points)
• Slide 3 of Toxin Research Project (worth +10 project points)
• Slide 4 of Toxin Research Project (worth +10 project points)

Remember, you can email me any time.  Office hours for Science are Tuesdays from 11am-12pm and Thursdays from 1pm-2pm.  Check your student Gmail for Zoom instructions.

Don’t forget to complete the Week 34 and Week 35 Bonus Credit Opportunities!  Check out the amazing artwork students are submitting as part of the Week 35 Bonus Credit Opportunity.

By now you are all wizards at balancing equations.  You know the number of atoms of each element must be the same on the reactant (left) side of the arrow as on the product (right) side of the arrow.  Let’s use a reaction you should be familiar with from the conservation of mass lab (Lesson 71): aqueous calcium chloride reacts with aqueous sodium carbonate to produce solid calcium carbonate and aqueous sodium chloride:

Here’s the balanced equation:

CaCl₂(aq) + Na₂CO₃(aq) → CaCO₃(s) + 2NaCl(aq)

Quick vocabulary review and a piece of important new learning:

• (aq) means aqueous (in water)
• (s) means solid
• In a chemical equation, the arrow points from the reactants toward the products.  As written above, the reactants are on the left and the products are on the right.
• The letters represent element symbols from the periodic table
• The numbers represent subscripts and coefficients.
  • Subscripts are the small integers (whole numbers) to the lower right of an element symbol and they cannot be changed.  Subscripts tell how many atoms of each element are present in a given molecule.  In the equation above, the small 2 after Cl tells us there are two chlorine atoms bonded with 1 calcium atom in one molecule of CaCl₂.
  • Coefficients are the regular-sized integers to the left of a molecule.  This is new and important: Coefficients tell us the correct mole ratio in which the reactants combine to form the products.  In the equation above, we now know that one mole of aqueous calcium chloride reacts with one mole of with aqueous sodium carbonate to produce one mole of solid calcium carbonate and two moles of aqueous sodium chloride.

Another example: N₂(g) + 3H₂(g) → 2NH₃(s)  This equation tells us that one mole of nitrogen gas reacts with 3 moles of hydrogen gas to produce one mole of solid ammonia.

Even more examples:

Your turn!  Complete the Mole Ratios Google Form before returning to Week 33 – Stoichiometry to continue working.

So far this week, we’ve learned that the coefficients of balanced equations provide us with mole ratios, which we can then use to predict the amount of products generated by reactants in a chemical reaction.  Once we have a theoretical value for the amount of reactant we will generate (our theoretical yield), we can then run the  experiment and measure how much reactant we actually recover (our actual yield).  By comparing the theoretical and actual yeilds, we can calculate our percent yield: how much reactant we are able to recover given real-world experimental constraints.

In the Going Through the Mole Tunnel section, we investigated the reaction of copper with silver nitrate to produce silver and copper nitrate.  We went on to calculate the number of moles of copper and silver nitrate we would have to combine to produce 30 g of silver.  Now, imagine we actually did that experiment and our recovery of pure silver was 28.5 g.  What was our percent yield of silver?

• Theoretical yield of silver = 30 g
• Actual yield of silver = 28.5 g

Percent yield = (actual yield) / (theoretical yield) x 100%

For our experiment: Percent yield = 28.5 / 30 x 100% = 95%

Not bad!  Our actual yield was only 5% less than our theoretical yield.  Why wasn’t the percent yield 100%?  Experimental error!  Maybe we mis-measured one of our reagents.  Maybe we used a solution that wasn’t prepared as accurately as it should have been.  Maybe our balance needs to be re-calibrated, or the volume measured by our beaker wasn’t perfectly accurate.

Another example:

Your turn!  Complete the Percent Yield Google Form before returning to Week 33 – Stoichiometry to continue working.