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.
Looking to earn some bonus credit and boost your grade? You’ve come to the right place! Each week, you will have the opportunity to earn bonus credit for completing extra learning about science…or practicing a scientific skill.
This week’s bonus credit opportunity is called…Write a Procedure. To earn credit this week, you have to write out the procedure for how to make something you love to eat, using ingredients you currently have access to. No special trips to the store! It doesn’t have to be a complicated procedure, but it does have to be extremely detailed. When you think you are finished, ask someone at home to read the procedure to you. Follow each step exactly as it is written. Can you make your food item? If more detail is required, revise your procedure and try again. When you have enough detail to complete the task, take a picture of your food item and upload it to the Google Form. The finished Procedure and uploaded picture together earn you +20 bonus points in the Lab Report category. Click here and fill out the Google Form.
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.
Your turn! Complete the Percent Yield Google Form before returning to Week 33 – Stoichiometry to continue working.
For the final part of our work this week, it’s time for college! Visit the UC Berkeley Understanding Evolution website and complete the following:
- In your Week 33 Google Doc, create a section titled “UC Berkeley Understanding Evolution”
- Read through the Co-evolution section (page 20) and answer the following question:
- How are Acacia plants and ants an example of co-evolution?
- Read through the Case Study of Co-evolution section (page 21 and page 22) and answer the following questions:
- Explain the co-evolutionary relationships between Red Squirrels, Crossbilled Birds, Lodgepole Pines.
- Read through the Biological warfare and the co-evolutionary arms race case study. Click the link to go to the first slide. There are 12 slides total. Read through the slides, then answer the following questions:
- What is co-evolution?
- How do living and non-living environments shape organisms through natural selection?
- How do evolutionary trade-offs restrict adaptation?
- How can we use the methods of science to answer questions about the natural world?
Return to the Week 33 – Co-Evolution post and continue our work for the week.
To wrap up our learning, here are a selection of excellent videos about our topic for this week’s learning: stoichiometry. In the textbook, we have covered content corresponding to lessons 91-93. I highly encourage everyone to read through those lessons. While the exercises will not be entered into Synergy, if you want to try some of the practice problems, email me your work and I will be happy to look it over and provide feedback.
Return to Week 33 – Stoichiometry and make sure you have everything complete for the week.
Welcome to Week 33! Last week, you constructed phylogenetic trees based on the relationships (like physical appearance, bird songs, and DNA sequences). For this week, we will be extending our study of evolution to include the process of co-evolution. Co-evolution occurs when two or more species interact over time, and influence each other’s evolution. Please work through the list of links below. Each section contains important information and ends with a portion of the weekly assignment. You can complete it all in one sitting or break it up as needed. Ready, set, go!
- Weekly Attendance Check-In
- Types of Biological Relationships (Google Doc assignment)
- Zombie Parasites (Google Doc assignment)
- Biological Warfare and the Co-Evolutionary Arms Race (Google Doc assignment)
You did it! Just to make sure, here’s a checklist of items you must complete this week by Sunday, May 10 at 11:59pm:
- Weekly Attendance Check-In (school district requirement)
- Biological Relationships Vocabulary section of Google Doc (worth 11 assignment points)
- Zombie Parasites section of Google Doc (worth 4 assignment points)
- UC Berkeley Understanding Evolution section of Google Doc (worth 20 assignment 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.
Finally, by popular demand…click here for the Week 33 Bonus Credit Opportunity!
Over the past few weeks, we have acquired a significant amount of evidence for evolution:
- Natural selection (the common ancestry of brown bears and polar bears; dinosaurs and chickens)
- Artificial selection (humans selecting for desired traits, such as dog breeding)
As we continue learning about evolution, we must expand our view to consider the concept of co-evolution:
- Co-evolution is the idea that organisms do not evolve in a vacuum. Evolution takes place concurrently in nature: populations of organisms influence each other’s evolution.
- The term co-evolution is used to describe cases where two (or more) species reciprocally affect each other’s evolution.
- Plants and insects represent a classic case of co-evolution — one that is often, but not always, mutualistic (keep reading – the definition of mutualism is further down). Many plants and their pollinators are so reliant on one another and their relationships are so exclusive that biologists have good reason to think that the “match” between the two is the result of a co-evolutionary process.
- For more about co-evolution, visit the evolution.Berkeley.edu website!
- Host: an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment (food) and shelter.
- Bacteria: microscopic living organisms, usually one-celled, that can be found everywhere. They can be dangerous, such as when they cause infection, or beneficial, as in the process of fermentation (to make foods like kimchi, fish sauce, Tabasco sauce, and salami) and that of decomposition.
- Virus: Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms.
- Infection: Invasion and multiplication of an infectious agent in body tissues of the host and may lead to clinical symptoms or local cellular injury as a result of competition in metabolism, production of toxins, intracellular replication, or antigen antibody response.
- Symbiosis: the interaction between two different organisms living in close physical association.
- Symbiotic Relationships:
- Mutualism: symbiosis that is beneficial to both organisms involved.
- Commensalism: an association between two organisms in which one benefits and the other derives neither benefit nor harm.
- Parasitism: a non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host.
- Create a Google Doc titled Week 33 – Your Name (Example: Week 33 – Olive Swart)
- Create a section in your Week 33 Google Doc titled “Biological Relationships Vocabulary”.
- Make a numbered list of each of the 11 words from this lesson highlighted in red bold text.
- For each word in your list, research your own examples of these biological processes, type of organisms, or relationships between organisms and write up your work in your Week 33 Google Doc. Include source citations as appropriate. Need some help getting started? Click here for examples of symbiotic relationships.
Return to the Week 33 – Co-Evolution post and continue our work for the week.