You'll investigate two real problems involving pH — a hazardous chemical spill and damaged farmland — and figure out how to fix them using acid-base chemistry.
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Scenario A — Lab Spill
The NaOH Incident
A 250 mL bottle of sodium hydroxide solution (NaOH) has spilled on a lab bench. The custodian is asking what to pour on it to neutralize it before cleanup. What do you recommend?
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Scenario B — Farmland
The Dying Crops
A farmer's soil test comes back at pH 4.2. Her wheat is stunted and yellowing. Most crops need pH 6–7 to absorb nutrients properly. What does she need to add to the soil, and why?
📖 Reference — pH, Acids & Bases, Neutralization
The pH Scale
0246791114
◀ AcidicNeutralBasic ▶
pH < 7 = acid · pH = 7 = neutral · pH > 7 = base
Each step of 1 on the pH scale is a 10× change in acidity. pH 2 is 100× more acidic than pH 4.
Acids
Release H⁺ ions in solution
pH below 7
Taste sour (lemon, vinegar)
Turn blue litmus red
React with metals and carbonates
Examples: HCl, H₂SO₄, CH₃COOH
Bases
Release OH⁻ ions in solution
pH above 7
Feel slippery; taste bitter
Turn red litmus blue
Examples: NaOH, Ca(OH)₂, NaHCO₃
Neutralization
When an acid and a base react, the H⁺ and OH⁻ ions combine to form water.
acid + base → salt + water
The products are a salt (ionic compound) and water. The pH moves toward neutral.
Section 1Investigate the Scenarios~20 min
Before you can solve either scenario, you need to know how acidic or basic the substances involved are. Use the pH Indicator Lab to find out, then fill in the table directly on this page.
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pH Indicator Lab
Drag substances into wells, apply indicators, and use the digital pH meter to measure each one. Opens in a new tab — come back here when you're done testing.
What to test
Use the pH meter on each substance below. Drain Cleaner represents the NaOH lab spill. Coffee is the closest match to the acidic farmland (pH 4.2) available in this sim.
1
Drag a substance into an empty well. Drag the pH meter onto the filled well and read the value shown.
2
Also apply pH Paper (the rainbow strip) to each well and note the colour.
3
Type your results directly into the table below. Your answers are saved automatically.
4
Double-click a well to clear it and test the next substance.
Substance
pH
pH Paper colour
Acid / Base / Neutral
Strong or Weak?
🍋 Lemon Juice
🫙 Vinegar
☕ Coffee
💧 Water
🥄 Baking Soda
🫧 Bleach
⚗️ Drain Cleaner
Question 1
Drain Cleaner represents the NaOH lab spill. Based on its pH, is it an acid, base, or neutral? Would you classify it as strong or weak? How do you know?
Question 2
The farmer's soil has a pH of 4.2. Which substance from your testing is the closest match? What type of substance does this tell you the soil is?
Question 3
For each scenario, which type of substance (acid or base) would you need to add to move the pH toward neutral? Pick one substance from your sim results as your proposed neutralizer for each scenario and explain your choice.
Section 2Plan the Response~30 min
Now that you know what type of substance each scenario involves, write the chemistry. For each scenario, complete the word equation and balanced chemical equation.
Scenario A — Lab Spill
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Realistic chemistry note
In a real lab, a NaOH spill is neutralized with dilute hydrochloric acid (HCl). The products are sodium chloride — table salt — and water.
Word Equation — fill in the products
sodium hydroxide+hydrochloric acid→+
Chemical Equation — balance it
NaOH+HCl→+
💡 Count Na, O, H, Cl on both sides. Make sure they match — you may need coefficients.
Question 4
Label each component in your equation above: which is the acid? The base? The salt product? What is the other product?
Question 5
After the neutralization reaction, predict whether the pH of the solution will be less than 7, equal to 7, or greater than 7. Explain why using the concept of neutralization.
Scenario B — Acidic Farmland
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What farmers actually do
Farmers add agricultural lime (calcium carbonate, CaCO₃) to acidic soil. It reacts with the acid, raises the pH, and releases CO₂ gas — you can see the soil fizzing.
Word Equation — fill in the missing product
calcium carbonate+sulfuric acid→+water+
Chemical Equation — fill in the products and balance
CaCO₃+H₂SO₄→+H₂O+
💡 Products are CaSO₄ (gypsum), water, and a gas. Count Ca, S, C, O, H on both sides.
Question 6
Write the complete, balanced chemical equation for the soil treatment reaction and name all four products.
Question 7
A farmer adds twice as much lime as needed. What do you predict happens to the soil pH — does it stop at neutral (pH 7), or could it overshoot? Explain your reasoning.
Section 3Advise the Farmer~15 min
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Closing Scenario
The Fertilizer Problem
The same farmer emails you for advice. Her soil is still at pH 4.2. She wants to apply ammonium sulfate fertilizer (pH ≈ 5.5) because it's cheaper than other options. Her neighbour says this is a terrible idea. Her fertilizer supplier says it'll be fine.
Who is right? Write a short memo (3–5 sentences) to the farmer explaining the problem and recommending a clear course of action. Use the word neutralization somewhere in your memo.
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Things to think about before you write
What happens when you add an acidic substance to an already-acidic one? What pH range do most crops need? What should the farmer do first, before applying any fertilizer?
Question 8 — Memo to the Farmer
Write your 3–5 sentence memo below. Your memo must:
✓ Explain why adding acidic fertilizer to acidic soil is a problem
✓ Reference a specific pH value or range
✓ Use the word neutralization
✓ Give a clear recommendation (what to do first, then what to do second)
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Early finisher extension
Go back to the pH Indicator Lab and explore the [H⁺]/[OH⁻] concentration calculator (bottom right). For Drain Cleaner (pH 13.5), what is the OH⁻ concentration? Compare it to water (pH 7.0). What does this tell you about why strong bases are so dangerous?
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