Weeks 34-35 – Limiting Reactants Revisited

Last week, you were introduced to the concept of limiting reactants.  In a chemical reaction, the limiting reactant is the chemical that is completely used up in the process of creating products.  When the limiting reactant is gone, the reaction ends.  Let’s imagine the chemical reaction of sodium bicarbonate (baking soda) and acetic acid (vinegar):

NaHCO3(s) + C2H4O2(aq) → NaC2H3O2(aq) + H2O(l) + CO2(g)

Let’s first notice that this equation is already balanced.  It does not require any coefficients to have equal numbers of atoms of each element on both sides of the equation.  One mole of solid sodium bicarbonate NaHCO3(s) reacts with one mole of aqueous acetic acid C2H4O2(aq) to produce one mole of aqueous sodium acetate NaC2H3O2(aq), one mole of liquid water H2O(l), and one mole of carbon dioxide gas CO2(g).

To determine how much of each substance we need to actually conduct this experiment, let’s calculate the molar masses of sodium bicarbonate and acetic acid:

  • NaHCO3 = 22.99 + 1.008 + 12.01 + (16.00 x 3) = 84.01 g/mol
  • C2H4O2 = (12.01 x 2) + (1.008 x 4) + (16.00 x 2) = 60.06 g/mol

Therefore, if we wanted to react one mole of sodium bicarbonate with one mole of acetic acid, we would need to combine 84.01 g of sodium bicarbonate with 60.06 g of acetic acid.  Easy!  We also know that we will produce one mole of carbon dioxide gas in this reaction – there will be bubbles!  Thinking back to our work with gas laws in Unit 3, we know that one mole of any gas at standard temperature and pressure will occupy a volume of 22.4 L.  So there will be a lot of gas bubbles!  Here is the reaction:

What did you observe?  Hopefully you noticed the geyser of bubbles – that was hard to miss!  Did you also notice the white solid material at the bottom of the flask?  That shouldn’t be there if the reactants fully reacted as expected.  The science tells us that one mole of sodium bicarbonate will fully react with one mole acetic acid.  Why was there so much unreacted sodium bicarbonate remaining?  Why was acetic acid the limiting reactant in this chemical reaction?

To answer this question, we need to look closely at our reactant labels:

The baking soda is pure sodium bicarbonate.  The distilled white vinegar has some fine print that says “distilled with water to 5% acid strength” – in other words, the distilled white vinegar actually contains 5% acetic acid and 95% water!  In our balanced equation, we assumed we were using 100% acetic acid, not 5% acetic acid.  Because 5% is 1/20 of 100%, we need to combine 20 times more of the 5% acetic acid (60.06 g x 20 = 1201.2 g) with 84.01 g of sodium bicarbonate to fully react both chemicals.  Or, we could keep the amount of acetic acid the same (60.06 g) and use 20 times less of the sodium bicarbonate (84.01 g / 20 = 4.2 g).  Let’s do that instead, to keep the amounts of each reagent reasonable:

What did you observe?  Can you explain it?  As we wind down the school year, this is an opportunity for you to earn credit in the lab report section of your chemistry grade.  This is an optional assignment and will be worth 50 bonus points. If your grade is not where you want it, and your lab report scores have been less than amazing, this is your chance to make up a lot of ground.  Please take advantage of it.

Lab Report Requirements:

    • Purpose: What are we trying to accomplish with this lab?
    • Procedure: Write out the steps, in order and in detail, that were followed in this experiment.
    • Results: What exactly did you observe?  Be clear, be descriptive, and include images if possible.
    • Conclusion: Clearly explain the results.  Include the concepts of chemical reaction, reactants, products, molar mass, and limiting reactant.

Note: If you have access to baking soda and vinegar and a safe space to work, you are welcome to substitute your own experimental data for what you were provided above.

Need some help setting up your lab report?  The links below will give you either a highly structured template specific to this lab, or a more generic template applicable to any lab report.  If you decide to use either one, click the link and then select File > Make a Copy and get to it!

Finally, if you have read all the way down to this point, enjoy!

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

Weeks 34-35 – The Evolution of Lactose Tolerance

Now that we better understand enzymes and how they work, it is time to focus on the enzyme lactase.  The substrate for lactase is lactose, a sugar commonly found in milk.  While you were briefly introduced to lactase in the previous work for this week, the video below will provide you with many important insights.

After watching the video, complete the Got Lactase? Google Form assignment.

Return to the Weeks 34-35 – Lactase Persistence post and continue our work for the week.

Weeks 34-35 – Toxin LD50 Calculations

For the final research part of the Toxin Research Project, it’s time to answer the question: how much is too much?  To answer that question, you need to research how much of your toxin is in a “standard dose” of your toxin.  “Standard dose” can be hard to find, and is often provided as a range.  For example, a “standard dose” of caffeine might be 100-200 mg per “dose” with a dose being an 8 ounce cup of coffee or a 12 ounce can of soda.  In that case, split the difference and use 150 mg as the standard dose for caffeine.  Buckle up – this is often the hardest part of this project.  Be persistent!  If “standard dose” doesn’t work as a search term, try “amount per serving” and see if that works.

Instructions for Slide 3:

  • Add Slide 3 to your Google Slides deck and title it “Toxin LD50 Calculations”
  • On Slide 3, answer the following:
    • Click the PubChem link to your toxin from Slide 1
    • Locate the molecular weight (synonym for molar mass) in PubChem and enter it on Slide 3
    • Using the molar mass and the LD50 (from Slide 1), calculate the lethal dose of the toxin for humans of three different masses and show your calculation work on the slide:
      • 10 kg
      • 30 kg
      • 75 kg
    • How many “standard doses” of the toxin does it take to reach the lethal dose for a person of mass 10 kg?  30 kg?  75 kg?

Here’s a video of my efforts to determine the “standard dose” of capsaicin per jalapeno pepper:

Need help bring these concepts together?  From the video above, we learned that the average jalapeño contains 2.24 mg of capsaicin.  Here is an example calculation for how many jalapeños a 75 kg person would have to eat to reach the lethal dose for capsaicin (identified in Slide 1 as 47.2 mg/kg):

75 kg x (47.2 mg capsaicin / 1 kg) x (1 jalapeños / 2.24 mg capcaisin) = 1580 jalapeños

When finished with Slide 4, return to Weeks 34-35 – How Much Is Too Much? and continue working.

Weeks 34-35 – Routes of Exposure

This week, you will be researching the question, How much is too much?  To begin, we will consider the four ways we can be exposed to a toxic substance:

  • Inhalation: breathing a toxic substance in through your mouth or nose
  • Absorption: skin or eye contact with a toxic substance
  • Ingestion: eating or drinking a toxic substance
  • Injection: puncture wound where the skin is pierced and a toxic substance is introduced into the body

In the high school science lab, we have a variety of ways to minimize risk to exposure to toxic substances.

  • Inhalation: Work with toxic gases in the fume hood, circulate air through open doors and windows, use the fan system in the room to circulate fresh air.
  • Absorption: Wear goggles to protect eyes, wear gloves to protect hands, wear aprons to protect bodies, wear long-sleeved shirts and pants to protect arms and legs, wear closed-toe shoes to protect feet.
  • Ingestion: Never, ever eat or drink in the lab.  This one is by far the hardest for students to understand.  Take a look at your bedroom – is it spotless?  How about your bathroom?  Odds are, both could use a good cleaning.  Assume the same with the lab space.  Never, ever eat or drink in the lab.  Assume something toxic was spilled on your lab bench the class before and the clean-up job was less-than-perfect.  It is easy to touch a contaminated bench top with your hands, then use your hands to eat or drink, thus causing you to inadvertently ingest a toxic substance.  For obvious reasons, this is why we never, ever, eat or drink anything produced in the lab.  Even if it were perfectly safe outside the lab, inside the lab we must always assume the labware used to conduct the experiment was previously contaminated with something toxic.  Rant over.
  • Injection: Never pick up broken glassware without proper safety equipment (i.e. gloves, tongs) as a toxic substance on the surface of broken glassware can enter your body if the glassware cuts you.

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

Weeks 34-35 – What is an Enzyme?

For starters, what is an enzyme?  From Simple English Wikipedia: Enzymes are protein molecules in cells which work as biological catalysts. Enzymes speed up chemical reactions in the body, but do not get used up in the process, therefore can be used over and over again. Almost all biochemical reactions in living things need enzymes.

To learn more about Enzymes, watch the video below and then complete the Enzymes Google Form assignment.  Note: after you submit the form, view your score.  You can re-submit the form if needed to improve your score.  Just make sure you improve your learning as well!

Take a breather from all that hard work and play a game of Google PAC-MAN.

Return to the Weeks 34-35 – Lactase Persistence post and continue our work for the week.

Weeks 34-35 – Toxicology

Toxicology is the the scientific study of the adverse effects of chemical substances on the living organism (Merriam-Webster).  In Slide 1, you identified the chemical structure of a toxin molecule.  In Slide 2, you will further define the biochemical properties of the molecule.  To begin, click on the link in Slide 1 and return to the PubChem database entry for your toxin molecule.

Instructions for Slide 2:

  • Add Slide 2 to your Google Slides deck and title it “Toxicology”
  • On Slide 2, answer the following:
    • How does the toxin interact with the human body?
      • Explain effects on the body as a whole, on specific organs, and at the cellular level.
      • Does the toxin act directly on cells, and if so, how?
      • Is the toxin metabolized by the kidneys or liver, and if so, how?
    • Are there treatments available for people who are exposed to the toxin?
      • If yes, how do treatments to the toxin work? Explain the mechanism of action for each treatment:
        • Does the treatment act against the toxin directly?
        • Does the treatment act on the body to protect against the toxin?
        • Does the treatment act on a metabolite produced after the toxin is metabolized by the liver or kidneys?
      • If no, look for evidence of failed treatments.
      • If you can’t find any information at all regarding treatment, propose a treatment and explain your thinking.

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 2.  You will also be provided with an example of Slide 2.
  2. Attend office hours on Tuesday and/or Thursday
  3. Email Mr. Swart with specific and detailed questions.

When finished with Slide 2, return to Weeks 34-35 – How Much Is Too Much? and continue working.

Weeks 34-35 – Graph of LD50

For the final slide of the Toxin Research Project, you will create a graph of the LD50 data from Slide 3.  You have many different options for creating the line graph, some of which include:

Instructions for Slide 4:

  • Add Slide 4 to your Google Slides deck and title it “Graph of LD50
  • Add your graph to Slide 4.  A complete graph includes:
    • Graph Title
    • X-axis Label (body mass (kg))
    • Y-axis Label (lethal dose (mass units from LD50 numerator))
    • Three coordinates (x,y) = (body mass, lethal dose) from Slide 3
    • A line connecting the three points
  • Determine the slope of the line.  What does it mean?

Need help? Click here for an example of a graph created using Google Sheets.

You did it!  Congratulations on completing the Toxin Research Project.  Be sure to share your Google Slides with Mr. Swart at david.swart@g.highlineschools.org and you should also share your hard work with everyone at home!

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