Week 1: Evidence of Chemical Reactions
Grade 8 Science | Rosche | Kairos Academies
The Fading Glow Mystery
Learning Targets
Crack a glow stick and it lights up - no batteries, no electricity, just a bright glow that slowly fades over hours until it's completely dark. What's happening inside?
- Identify five types of evidence for chemical reactions
- Distinguish between chemical and physical changes
- Explain that mass is conserved during chemical reactions
- Design investigations to detect chemical reactions
Hook
Hook: The Fading Glow Mystery
Key Observations
- Fresh glow stick: Instant bright glow when cracked
- After several hours: Glow becomes dimmer
- After a day or more: Completely dark
- Cannot be "recharged" - unlike a battery!
Hook Form
Form will be embedded here by your teacher
Worked Example
Step-by-Step Problem Solving
COMMON MISTAKE ALERT: "Mass Disappears When Things
Burn"
WRONG: "When wood burns, the mass disappears as
smoke."
RIGHT: "Mass becomes CO₂ and water
vapor gases that escape—if captured, total mass stays the same!"
KEY:
Atoms are NEVER destroyed. They just rearrange into different
molecules (often gases).
Problem Scenario
Review the problem scenario and work through each step below.
Step-by-Step Problem Solving
COMMON MISTAKE ALERT: "Mass Disappears When Things Burn"
WRONG: "When wood burns, the mass disappears as
smoke."
RIGHT: "Mass becomes CO₂ and water
vapor gases that escape—if captured, total mass stays the same!"
KEY:
Atoms are NEVER destroyed. They just rearrange into different
molecules (often gases).
Problem Scenario
Review the problem scenario and work through each step below.
Station 1
Station 1: Reaction Evidence Lab
Five Types of Reaction Evidence
| Evidence Type | What to Look For | Example |
|---|---|---|
| Color Change | New color appears that wasn't in either reactant | pH indicator turning pink |
| Gas Production | Bubbles, fizzing, or foam | Baking soda + vinegar |
| Temperature Change | Gets hot (exothermic) or cold (endothermic) | Hand warmer heating up |
| Precipitate | Solid appears from mixing liquids | White solid from clear solutions |
| Light Production | Glowing without being heated | Glow stick (chemiluminescence) |
Interactive Simulation: Reactants, Products, and Leftovers
How to Use This Simulation:
- Start with the "Sandwiches" tab - this models chemical reactions using food!
- Watch what happens: 2 bread + 1 cheese → 1 sandwich (just like reactants → products)
- Switch to "Molecules" tab: Try the reaction 2H₂ + O₂ → 2H₂O (making water!)
- Observe leftovers: What happens when you have extra reactants? They don't disappear!
- Experiment with ratios: Add different amounts of reactants and count what's left over
- Connect to mass conservation: Count all atoms before and after - they're always equal!
Need help getting started with the simulation?
If the simulation won't load:
- Try refreshing your browser (Ctrl+R or Cmd+R)
- Make sure you're connected to Wi-Fi
- Ask Mr. Rosche for help if it still doesn't work
What to observe:
- Chemical reactions need specific ratios of reactants (like recipes!)
- Leftover reactants don't participate - they stay unreacted
- The "Before" and "After" boxes show mass conservation: same atoms, just rearranged
- This simulation demonstrates the Law of Conservation of Mass!
Interactive Simulation: Chemical Reaction Evidence Explorer
How to Use This Simulation:
- Visit all 5 stations - each demonstrates a different type of reaction evidence
- Click to trigger reactions - add reagents, mix solutions, or crack the glow stick
- Toggle particle view to see bonds breaking and forming at the molecular level
- Check off observations as you identify each evidence type
- Complete the data table by recording evidence from all 5 stations
Need help with the simulation?
The 5 types of evidence:
- Color Change: Phenolphthalein turns pink when a base is added
- Gas Production: Baking soda + vinegar creates CO₂ bubbles
- Temperature Change: Calcium chloride + water releases heat
- Precipitate: Silver nitrate + salt forms white AgCl solid
- Light Production: Glow stick chemicals produce chemiluminescence
Station 1 Form
Form will be embedded here by your teacher
Station 2
Station 2: Mass Conservation Investigation
Understanding Mass Conservation
| System Type | What Happens | Mass Observation |
|---|---|---|
| Sealed Container | Nothing can enter or leave | Mass stays exactly the same |
| Open Container | Gas can escape to the air | Mass appears to decrease |
Why Does Burning Wood Seem to "Lose" Mass?
When wood burns, most of it combines with oxygen and escapes as gases (CO₂ and H₂O vapor). The ash is just the minerals that couldn't burn. If you could capture ALL the gases, total mass would be conserved!
WORKED EXAMPLE: Analyzing Mass Conservation
Learn by following an expert's thinking process. Week 1 shows ALL steps.
PROBLEM:
A sealed flask contains 100.0 g of baking soda + 50.0 g of vinegar. After mixing (a chemical reaction occurs), gas fills the flask and the mass reads 150.0 g. An identical unsealed flask shows 142.3 g after the same reaction. Explain both results using conservation of mass.
STEP 1: Identify the system and predict based on conservation
Expert thinks: "First, let me organize what I know:"
- Starting mass (both flasks): 100.0 g + 50.0 g = 150.0 g total
- This reaction produces CO₂ gas (baking soda + vinegar → salt + water + carbon dioxide)
- Sealed flask can't lose gas; unsealed flask CAN lose gas
- "If mass is conserved, sealed should stay 150.0 g; unsealed should show less"
STEP 2: Analyze the sealed flask result
Expert reasons:
- Final mass: 150.0 g (SAME as starting mass)
- CO₂ gas was produced but couldn't escape
- All products (salt, water, CO₂) remain in the flask
- "This CONFIRMS conservation of mass - all atoms are still there, just rearranged!"
STEP 3: Analyze the unsealed flask result
Expert calculates:
- Final mass: 142.3 g (LESS than starting 150.0 g)
- Missing mass: 150.0 - 142.3 = 7.7 g
- This is CO₂ that escaped to the air!
- "Mass appears to decrease, but it's not destroyed - it left the system"
STEP 4: Construct complete explanation
Expert writes:
"Both results demonstrate conservation of mass. The sealed flask maintains exactly 150.0 g because ALL products (including 7.7 g of CO₂ gas) remain trapped inside. The unsealed flask shows only 142.3 g because 7.7 g of CO₂ gas escaped to the atmosphere. If we could capture and weigh that escaped gas, the total would still be 150.0 g. Mass is never created or destroyed in chemical reactions - atoms are only rearranged."
SELF-EXPLANATION PROMPT:
A piece of steel wool (5.0 g) is burned in an open container. After burning, the rust weighs 6.5 g - MORE than the original! Does this violate conservation of mass? Explain using the same reasoning strategy. (Hint: What invisible reactant combined with the iron?)
Station 2 Form
Form will be embedded here by your teacher
Station 3
Station 3: Design a Reaction Detector
Why This Matters to YOU
- Health & Safety: Foodborne illness from spoiled products affects 48 million Americans yearly. Chemical reaction detection prevents food poisoning outbreaks and saves lives.
- Environment: 30-40% of US food supply is wasted. Better spoilage detection could reduce waste, saving resources and reducing methane from landfills.
- Careers: Food scientists and quality assurance specialists earn $60k-$90k/year developing detection systems for freshness, contamination, and chemical safety in food production.
- Your Daily Life: Smart packaging already uses pH indicators (chemical reaction detection!) - you've seen color-changing labels on meat, milk, and medicine showing freshness.
The Science Behind Spoilage
- What happens: Bacteria convert lactose (milk sugar) → lactic acid
- Evidence: pH drops from ~6.6 (fresh) to ~4.5 (spoiled)
- Your tool: pH indicators change color at specific pH values
Design Requirements
- Must use at least one type of reaction evidence
- Must be food-safe (no contamination)
- Must give a clear visual signal
- Should work over the product's shelf life
YOUR CHOICE: Select Your Detection Approach
You have THREE design approaches for this food safety challenge. Choose the one that interests you most! All three can earn full points.
Option A: pH Indicator Strip (Chemical Evidence)
Design a strip embedded in the milk cap that changes color based on pH. Fresh milk (pH 6.6) = green indicator. Spoiled milk (pH 4.5) = red indicator. Simple, visual, direct chemical evidence. If you value simplicity and direct measurement, choose this path.
Option B: Temperature + Gas Detection (Multi-Evidence)
Design a smart cap that detects BOTH heat (exothermic bacterial growth) and gas production (CO₂ from fermentation). Uses temperature sensor + pressure sensor. More complex but detects spoilage earlier. If you value comprehensive data and early warning, choose this path.
Option C: Time-Temperature Integration (Predictive)
Design a system that tracks cumulative heat exposure over time. Reaction rate doubles every 10°C - your indicator integrates this to predict spoilage before it happens. Most sophisticated approach. If you value predictive analytics and proactive safety, choose this path.
All three approaches are used in real food packaging! Choose based on your engineering values, not what seems "easiest." You'll justify your choice using chemical reaction principles.
Station 3 Form
Form will be embedded here by your teacher
Exit Ticket
Exit Ticket
Exit Ticket Structure
- 2 NEW questions: Reaction evidence, mass conservation
- 2 SPIRAL questions: Cycle 6 (energy), Cycle 5 (light waves)
- 1 INTEGRATION: Connect energy release to evidence
- Analyze reaction data
YOUR CHOICE: How to Show Your Understanding
For the INTEGRATION question (connecting energy release to chemical reaction evidence), you choose how to respond:
All three formats can earn full points! Choose the format that helps YOU think most clearly about energy and evidence connections.
Exit Ticket Form
Form will be embedded here by your teacher
Key Vocabulary
Vocabulary
Cognate Strategy: Many science words look similar in English and Spanish — use your Spanish to learn science!
| Term | Spanish | Definition |
|---|---|---|
| Chemical Reaction | Reacción química | Proceso donde sustancias se combinan o separan para formar nuevas sustancias / Process where substances combine or break apart to form new substances |
| Reactant | — | Reactivo |
| Product | — | Producto |
| Exothermic | Exotérmico | Reacción que libera calor (se siente caliente) / Reaction that releases heat (feels warm) |
| Endothermic | Endotérmico | Reacción que absorbe calor (se siente frío) / Reaction that absorbs heat (feels cold) |
| Precipitate | — | Precipitado |
| Conservation of Mass | Conservación de masa | Masa antes de reacción = masa después de reacción / Mass before reaction = mass after reaction |
Environmental Justice: Chemical Safety in St. Louis Communities
St. Louis's Industrial Chemical Burden
St. Louis has a long history as an industrial center, with chemical manufacturing and processing facilities concentrated along the Mississippi River industrial corridor. Communities in North St. Louis and South City—predominantly low-income neighborhoods with large Black populations—live near industrial zones, breathing air contaminated by chemical reactions from nearby manufacturing plants and facilities. Residents report seeing, smelling, and tasting pollution daily. These same chemical reactions you're studying (combustion, synthesis, decomposition) create toxic byproducts that cause elevated cancer rates and childhood asthma in fence-line communities.
Chemical Evidence of Harm
The five types of reaction evidence you learned today—color change, gas production, temperature change, precipitates, and light—aren't just classroom concepts. They're how communities detect danger. When chemical plants have accidents, residents see color changes in the air (nitrogen dioxide's brown haze), smell gases (hydrogen sulfide's rotten egg odor), and feel temperature changes from fires. Industrial accidents at chemical facilities have released toxic substances into St. Louis neighborhoods, where residents used their senses to detect reaction evidence and evacuated before official warnings arrived.
Taking Action with Chemistry Knowledge
Understanding chemical reactions empowers you to protect your community. Organizations like the Missouri Coalition for the Environment train residents to use low-cost air monitors that detect reaction products (gases, particulates) in real-time. When you know what evidence indicates a chemical reaction, you can identify pollution sources, document violations, and demand accountability. Environmental justice means everyone deserves to live without toxic chemical exposure—regardless of income, race, or ZIP code. Your chemistry knowledge is a tool for change.
Practice These Vocabulary Terms
Scientist Spotlight: Dr. Emmett Chappelle
From Farm to NASA
Dr. Emmett Chappelle (1925-2019) grew up on a farm in Arizona with no electricity, yet he became one of NASA's leading experts on chemiluminescence—the same light-producing reaction that makes glow sticks work. As a Black scientist during the segregation era, he faced enormous barriers but earned a master's degree in biology and worked at NASA for over three decades, transforming how we detect life and chemical reactions.
Chemistry That Glows
Dr. Chappelle specialized in bioluminescence and chemiluminescence—chemical reactions that produce light without heat (like the glow sticks in this week's phenomenon!). He discovered that all living cells produce a chemical called ATP, and when ATP reacts with an enzyme called luciferase, it releases light. This reaction became his "life detection" tool. NASA used Dr. Chappelle's methods to search for bacterial contamination in spacecraft, detect microbes in soil samples, and even look for signs of life on other planets.
Career Achievements
- Education: B.S. in Biology (UC Berkeley), M.S. in Biology (University of Washington)
- NASA Career: Research scientist (1966-2001) studying bioluminescence and photosynthesis
- Patents: 14 U.S. patents for detection methods using light-producing reactions
- Legacy: Developed rapid methods to detect bacteria in food, water, and medical settings
Impact Beyond Space
Dr. Chappelle's work didn't stay in space—it revolutionized food safety, water quality testing, and medical diagnostics on Earth. His light-based detection methods allowed scientists to identify bacterial contamination in minutes instead of days. Today, food processing plants, water treatment facilities, and hospitals use technologies based on his chemiluminescence research to keep people safe. "I wanted to use chemistry to solve real problems," he said. "Light-producing reactions gave us a window into invisible worlds."
St. Louis Connection: This Affects YOU
St. Louis is home to major pharmaceutical companies like Mallinckrodt and chemical manufacturers. When these facilities produce medicines or industrial chemicals, they use the same chemical reactions you're studying—synthesis, decomposition, and combustion. Understanding reaction evidence helps you identify when something goes wrong: unusual colors in discharge water, unexpected gases from smokestacks, or temperature changes indicating runaway reactions. This chemistry knowledge empowers you to monitor industrial safety in your own community.
Need Extra Support? Click Here
Tier 2 Supports
- Reaction evidence chart - Reference sheet with all five evidence types
- Chemical vs physical comparison - Side-by-side examples
- Vocabulary visual guide - Diagrams for key terms
Sentence Starters
- "This is a chemical reaction because I observed..."
- "Mass is conserved because..."
- "The evidence that a reaction occurred is..."
- "The difference between chemical and physical change is..."
Tier 3 Supports
- One-on-one observation support - Work with teacher on evidence identification
- Modified mass conservation demo - Simplified sealed container experiment
- Visual sorting activity - Sort examples into chemical/physical categories
Enrichment & Extension
Optional deep dives for early finishers.
Optional content if you finish early or want to go deeper.
Scientist Spotlight
Research a scientist who contributed to this week's topic area and describe their key findings.
Environmental Justice Connection
Explore how this week's science concepts connect to environmental justice issues in our community.
Week 1 Complete!
Great work exploring Evidence of Chemical Reactions this week!