Week 2: Reaction Types & Conservation
Grade 8 Science | Rosche | Kairos Academies
Accessibility & Learning Support
- Text-to-speech: Right-click any text → "Read aloud" (Chrome) or use the speaker icon (Edge)
- Working from home? See the section below for at-home instructions
- Need extra help? Click the green "Need help?" buttons for hints and scaffolds
St. Louis Connection: This Affects YOU
St. Louis's water treatment facilities use double replacement reactions to remove heavy metals from drinking water—the same precipitation reactions you're learning in Station 3. When lead contamination was discovered in North St. Louis homes (from aging pipes), water utilities had to use chemical treatment (adding phosphates to precipitate lead out of solution) to protect residents. Understanding reaction types helps you evaluate whether your city's water treatment is adequate and demand better chemistry when it's not.
Working From Home?
- All forms: Work completely online - no physical materials needed
- PhET simulations: Use the embedded links - they work on any device
- Time: Budget ~75 minutes total (breaks between stations are okay!)
- Questions? Email Mr. Rosche before starting if you're confused
Hook
Hook: The Disappearing Solid Mystery
Imagine pouring two perfectly clear liquids together. The instant they touch, a white solid magically appears and sinks to the bottom! Neither liquid contained a solid, yet one forms instantly.
Where did the atoms come from? They were rearranged from both liquids in what chemists call a double replacement reaction!
Common Misconception
Wrong: "New atoms were created in the reaction."
Correct: Atoms are NEVER created or destroyed. They just rearranged from the liquids into a new solid compound.
Hook Form
Form will be embedded here
Need Extra Support?
Think about it: The solid that appears is called a precipitate (preh-SIP-ih-tate). The atoms in both liquids swapped partners to form it!
Tier 3Sentence starter: "The solid appeared because the atoms from ______ and the atoms from ______ rearranged to form ______."
Worked Example
Step-by-Step Problem Solving
COMMON MISTAKE ALERT: "Changing Subscripts to Balance
Equations"
WRONG: "Change H₂O to H₂O₂ to balance the
equation."
RIGHT: "Only change coefficients
(numbers in front). Subscripts define the substance—changing them
makes a completely different chemical!"
KEY: H₂O
is water. H₂O₂ is hydrogen peroxide (bleach). Never change subscripts
to balance!
Problem Scenario
Review the problem scenario and work through each step below.
Step-by-Step Problem Solving
COMMON MISTAKE ALERT: "Changing Subscripts to Balance Equations"
WRONG: "Change H₂O to H₂O₂ to balance the
equation."
RIGHT: "Only change coefficients
(numbers in front). Subscripts define the substance—changing them
makes a completely different chemical!"
KEY: H₂O
is water. H₂O₂ is hydrogen peroxide (bleach). Never change subscripts
to balance!
Problem Scenario
Review the problem scenario and work through each step below.
Station 1
Station 1: Reaction Type Classification
Five Types of Chemical Reactions
| Type | Pattern | Example | Everyday Connection |
|---|---|---|---|
| Synthesis | A + B → AB | 2H₂ + O₂ → 2H₂O | Making water from hydrogen & oxygen |
| Decomposition | AB → A + B | 2H₂O → 2H₂ + O₂ | Electrolysis splits water |
| Single Replacement | A + BC → AC + B | Zn + CuSO₄ → ZnSO₄ + Cu | Coating objects with copper |
| Double Replacement | AB + CD → AD + CB | NaCl + AgNO₃ → NaNO₃ + AgCl | Making photography chemicals |
| Combustion | Fuel + O₂ → CO₂ + H₂O | CH₄ + 2O₂ → CO₂ + 2H₂O | Burning natural gas for heat |
- Synthesis = "put together" (syn- means together)
- Decomposition = "break apart" (de- means down)
- Replacement = "swap partners" (like switching dance partners!)
- Combustion = "burn with oxygen" (always produces CO₂ + H₂O)
Interactive Simulation: Reaction Type & Equation Balancer
How to Use This Simulation:
Two modes to master:
- Classification Mode: Watch animated reactions and identify the type (synthesis, decomposition, single/double replacement, combustion)
- Balancing Mode: Use +/- buttons to adjust coefficients until atoms balance on both sides
- Watch the visual atoms update as you change coefficients
- Check the atom counter to verify your balance
- Remember: Only change coefficients, NEVER subscripts!
Need help with the simulation?
Classification tips:
- Count reactants and products to identify the pattern
- 1 reactant to 2+ products = Decomposition
- 2+ reactants to 1 product = Synthesis
- Fuel + O₂ always = Combustion
Balancing tips:
- Balance one element at a time
- Start with metals, end with O and H
- Total atoms of each element must match on both sides
Station 1 Form
Form will be embedded here
Need Extra Support?
Classification strategy:
- Count the reactants (left side) - 1 or 2?
- Count the products (right side) - 1 or 2?
- 1 reactant → 2 products = Decomposition
- 2 reactants → 1 product = Synthesis
- 2 reactants → 2 products = Replacement (check if single or double)
Sentence starter: "This is a ______ reaction because the reactants ______ to form ______."
Station 2
Station 2: Balancing Equations Lab
Coefficients vs. Subscripts
| Term | Symbol | What It Means | Can You Change It? |
|---|---|---|---|
| Coefficient | 2H₂O | How many molecules (2 water molecules) | YES - This is how you balance! |
| Subscript | H2O | How many atoms per molecule (2 H per water) | NO - This changes the substance! |
Common Misconception
Wrong: "Change subscripts to balance equations."
Correct: Changing subscripts creates a DIFFERENT substance! H₂O₂ (hydrogen peroxide) is very different from H₂O (water). Only adjust coefficients!
- Count atoms on each side
- Adjust coefficients ONLY (never subscripts!)
- Re-count to verify equal atoms on both sides
- Reduce to smallest whole numbers if needed
Station 2 Form
Form will be embedded here
Need Extra Support?
Atom counting table: Create a T-chart with "Reactants" and "Products" columns. List each element and count how many atoms appear on each side.
Tier 3Visual model: Draw each atom as a circle. Make sure you have the same number of each color circle on both sides of the arrow.
Station 3
Station 3: Design a Chemical Process
The Problem
Lead (Pb²⁺) ions in drinking water cause serious health problems, especially for children. You need to design a chemical process to remove lead using what you've learned about reaction types.
The Chemical Solution
- Add a chemical that provides ions to react with lead (e.g., NaCl provides Cl⁻)
- Lead ions combine with chloride ions: Pb²⁺ + 2Cl⁻ → PbCl₂(s)
- The precipitate (solid PbCl₂) can be filtered out of the water
- Dispose of precipitate as hazardous waste (it still contains toxic lead!)
Design Constraints
- Must remove at least 95% of lead ions
- Treatment chemicals must be safe and affordable
- Process must work at room temperature
- Must dispose of waste safely
Station 3 Form
Form will be embedded here
Need Extra Support?
Process checklist:
- What chemical will you add? Why?
- What reaction type is this? (Double replacement)
- What product forms? (A precipitate)
- How will you remove the precipitate? (Filtration)
Sentence frames:
- "I will add ______ to the water because..."
- "The lead will react with ______ to form..."
- "I can remove the solid by..."
Exit Ticket
Question Structure
| Type | Count | Focus |
|---|---|---|
| NEW | 2 | Reaction types, balancing equations |
| SPIRAL | 2 | Week 1 reaction evidence, Cycle 6 energy |
| INTEGRATION | 1 | Connect reaction types to conservation of mass |
| SEP-6 | 1 | Construct scientific explanation |
Exit Ticket Form
Form will be embedded here
Need Extra Support?
Use the vocabulary section and reaction type table as references while completing the exit ticket.
Tier 3For explanation questions: Use this frame: "The reaction shows conservation of mass because ______ atoms on the left equals ______ atoms on the right."
Environmental Justice: Chemical Exposure & Community Health
Unequal Chemical Burdens
The chemical reactions you're learning about don't impact all communities equally. Low-income neighborhoods and communities of color are disproportionately exposed to toxic chemicals from industrial facilities. In the United States, people of color are exposed to 40% more particulate air pollution than white communities, and they experience higher rates of lead poisoning, asthma, and cancer linked to chemical exposures.
Lead contamination—the topic of today's Station 3—is a prime example. Even after lead paint and leaded gasoline were banned, millions of homes in older neighborhoods still contain lead pipes and paint. Cities like Flint, Michigan made national headlines when cost-cutting decisions exposed predominantly Black residents to lead-contaminated drinking water. Lead interferes with children's brain development, causing irreversible learning disabilities.
St. Louis's Industrial Corridor & Local Environmental Justice
Right here in St. Louis, the Mississippi River industrial corridor runs through communities in North St. Louis and South City—home to significant chemical manufacturing and processing capacity. Predominantly African American and low-income residents live downwind from chemical plants, manufacturing facilities, and industrial zones. These double replacement, synthesis, and combustion reactions (the types you're studying) run 24/7, releasing criteria pollutants and toxic organic compounds. Residents in these neighborhoods experience asthma rates 2-3x higher than affluent St. Louis areas and face elevated cancer risks. The lead removal process you learned in Station 3 is exactly what water treatment plants in North St. Louis struggle with when industrial discharge contaminates water supplies. Understanding these reactions empowers you to advocate for stronger emissions controls and remediation in your own community.
Industrial Pollution Patterns
Chemical manufacturing plants, oil refineries, and waste incinerators are more likely to be located near communities with less political power. These facilities release toxic chemicals through double replacement reactions (like the ones you're studying), combustion reactions that create air pollution, and decomposition reactions that break down waste. Residents breathing this air face elevated cancer risks and chronic respiratory diseases.
Why Chemistry Matters for Justice
Understanding reaction types empowers you to demand change. When you know how lead precipitates from water (Station 3), you can evaluate whether your city's water treatment is adequate. When you understand combustion reactions, you can analyze air quality data and advocate for cleaner industrial processes. Environmental justice means everyone deserves clean air, clean water, and freedom from toxic exposure—regardless of race or income. As future scientists, engineers, and citizens, you have the knowledge to make that vision real.
Scientist Spotlight: Dr. Mae Jemison
From Chemistry Class to Space
Dr. Mae Jemison became the first African American woman in space in 1992, but her journey started with chemistry. Growing up in Chicago, she was fascinated by how substances react and transform—the same reaction types you're learning this week. She studied chemical engineering at Stanford University, focusing on how reactions occur in living systems (biomedical engineering).
Chemistry in Medicine & Space
After earning her medical degree, Dr. Jemison joined the Peace Corps, using her chemistry knowledge to ensure safe water supplies and prevent disease in West Africa—work directly related to precipitation reactions like the lead removal you explored in Station 3. When NASA selected her as an astronaut, her chemistry expertise proved essential. In space, she conducted experiments on how chemical reactions behave in microgravity, including studying how materials synthesize under different conditions.
Career Pathway
- Education: B.S. in Chemical Engineering (Stanford), M.D. (Cornell Medical School)
- Early career: Physician with Peace Corps in Sierra Leone and Liberia
- NASA years: Mission specialist on Space Shuttle Endeavour (1992)
- Current work: Founder of technology companies; STEM education advocate
Why Chemical Engineering?
"I wanted to understand how things work at the molecular level," Dr. Jemison explains. "Chemistry gives you power to solve problems—from creating medicines to purifying water to developing new materials." Today, she leads initiatives to bring science and technology to underserved communities, showing that diverse perspectives make science stronger.
Key Vocabulary
Quick Reference: Identifying Reaction Types
| If you see... | It's probably... | Pattern |
|---|---|---|
| Two substances combining into one | Synthesis | A + B → AB |
| One substance breaking into two or more | Decomposition | AB → A + B |
| An element replacing part of a compound | Single Replacement | A + BC → AC + B |
| Two compounds swapping partners | Double Replacement | AB + CD → AD + CB |
| Something burning with O₂, producing CO₂ + H₂O | Combustion | Fuel + O₂ → CO₂ + H₂O |
Practice These Vocabulary Terms
🆘 Stuck on a Question? Try These Strategies
Test-Taking Strategies
- Read the ENTIRE question before answering
- Identify the reaction type first - this helps with all other questions
- Count atoms carefully - make a T-chart if needed
- Check your work - do atoms balance on both sides?
- Skip difficult questions and return to them later
- Use the vocabulary section to remind yourself of definitions
For Balancing Equations
- Start with the most complex molecule
- Balance metals first, then non-metals
- Save hydrogen and oxygen for last
- Double-check by counting ALL atoms on both sides
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 2 Complete!
Great work exploring Reaction Types & Conservation this week!