Day 3: Wild Rivers Water Park Mystery

Welcome, investigators.

Wild Rivers Waterpark in Irvine has a problem. Guests are reporting weird smells in the lazy river, a sour taste near one of the slides, and bubbles forming in the kiddie pool. Maintenance is stumped. Today your team gets called in.

🔍 The Mystery

Six water samples have been collected from across the park. Each location has a complaint attached. Your job: figure out which samples are dangerous, identify what's contaminating them, and write up a report Wild Rivers can act on.

Your tools today:
  • Red cabbage juice — a natural pH indicator that changes color based on acidity
  • pH test strips — for confirming your cabbage juice readings with a number
  • A printed pH color chart at every table
The six sample locations
  1. Castaway River (the 1,700-ft lazy river) — guests report a sharp chemical smell
  2. Kontiki Cove (kiddie pool) — strange bubbles forming on the surface
  3. Shaka Bay (wave pool) — water tastes weird; lifeguards noticed maintenance added something extra this morning
  4. Pacific Grille (drinking fountain) — the baseline sample; nothing reported wrong
  5. Tiki's Revenge (bowl slide) — sour smell after morning cleaning
  6. Mustang Bar (poolside dining area) — sticky residue around the fountain pump
🧪 The Science of pH

pH is a number from 0 to 14 that tells you how acidic or basic a liquid is.

  • Below 7 → acidic
  • Exactly 7 → neutral (pure water)
  • Above 7 → basic / alkaline

Red cabbage juice contains pigments called anthocyanins that change color when they react with acids or bases. The same molecules that make cabbage purple make slime glow under certain conditions and give blueberries their color. They're nature's pH indicator.

Cabbage juice color chart
pH 1–2
Red
pH 3–4
Pink
pH 5–6
Light purple
pH 7
Purple
pH 8–9
Blue
pH 10–11
Teal/green
pH 12+
Yellow-green

Your printed chart will show closer-to-true colors than what you see on screen.

Why use both cabbage juice AND pH strips? The cabbage juice gives you an instant visual answer — fast, but a range, not a precise number. The pH strips give you a confirmed number to put in your report. Real water quality labs always use multiple tests to confirm a single reading.
🧫 Test Every Sample

You'll make your cabbage juice indicator first, then collect your samples from the central sample table, then run the three-step pH test on each tube — strip BEFORE cabbage, cabbage juice, strip AFTER cabbage. Work through one tube at a time and record on your handout as you go.

⚠️ Safety first. Goggles on before you start. These samples may contain trace cleaning products or pool chemicals — treat every sample as if it could irritate skin or eyes. Don't sniff the cups. If anything spills on skin, rinse with water and tell your teacher.
Instructions
Part I: Make the cabbage juice indicator
Materials at your table (per pair)
  • Red cabbage pieces in a zip bag
  • A small cup to pour the juice into
  • 1 rack of six 15mL test tubes (3D printed stand — your pair shares this set)
  • pH test strips — you'll use 2 per sample (12 total per pair). The chart on the strip container is "pH chart 1" on your handout.
  • A small stack of fresh droppers (you'll use one per tube for the cabbage juice step)
  • Goggles for both of you
  • Printed pH color chart for the cabbage juice
  • Your 📋 Water Mystery handout

Numbered sample bottles are at the central sample table — one bottle per location, labeled 1 through 6. Each bottle has its own dedicated dropper that stays with that bottle.

  1. Seal the cabbage bag tightly.
  2. Crush the cabbage with your hands until the liquid inside turns deep purple. The more you crush, the more pigment you release.
  3. Carefully pour or squeeze the cabbage juice out of the bag into your small cup.
  4. Set it aside. You'll add it to each sample one at a time in Part III.
Instructions
Part II: Collect your samples

Bring your test tube rack to the central sample table. Each numbered sample bottle matches a numbered test tube position in your rack.

Critical rule: Each sample bottle has its own dedicated dropper. Never move a dropper from one bottle to another — that's how samples get contaminated and ruined for the next team.
  1. Use bottle 1's dropper to put 5–6 mL from bottle 1 into tube 1 in your rack. (About a third of the way up the tube.) Return the dropper to bottle 1.
  2. Use bottle 2's dropper for tube 2. Bottle 3's dropper for tube 3. Repeat for all six. Each dropper stays with its bottle.
  3. Double-check the numbers match before you walk back.
  4. Carry the rack carefully back to your table.

The number on each tube corresponds to a Wild Rivers location. Your 📋 Water Mystery handout has the location list — match each numbered tube to its location as you record data.

Instructions
Part III: Run the three-step pH test on each tube

Work through one tube completely — all three steps — before moving to the next. Record every observation on your 📋 Water Mystery handout as you go.

For each test tube:
  1. pH BEFORE. Dip a pH strip into the tube for about 2 seconds. Match the color to the chart on the strip container (pH chart 1). This is your most accurate reading — done on the pure sample, before anything else goes in. Record it in the ACTUAL pH column on your handout (Acidic, Neutral, or Basic).
  2. Cabbage juice. Use a fresh dropper to add several drops of cabbage juice to the tube. Swirl gently. Watch the color change — the reaction is almost instant. Match the color to the pH scale at the top of your handout (pH chart 2) and record the observed color in the OBSERVED COLOR column. Set the dropper aside — don't reuse it on the next tube, or you'll carry color backwards.
  3. pH AFTER. Dip a fresh pH strip into the same tube (now with cabbage juice mixed in). Compare to the pH BEFORE reading. Did the number shift? By how much? Use this to fill in the WHAT THIS SUGGESTS column — Normal or Problem — and write a quick note about what might be contaminating the sample.
Why test pH before AND after the cabbage juice? Cabbage juice has its own pH — about 5 — so it's already slightly acidic. When you mix it into an extreme sample, it pulls the reading toward the middle. That's why pH BEFORE is your most accurate number — the pure sample, no contamination. The pH AFTER reading shows you how much the cabbage juice shifted things. If pH AFTER barely moved from pH BEFORE, your sample is close to cabbage's natural pH. If it shifted a lot, your sample is extreme. Both readings tell you something.

When you're done, you'll have a rack of 6 test tubes showing 6 different colors — your case in living color, side by side.

📋 Build Your Case

Look at all 6 samples side by side. Now you're not just testing — you're investigating.

Instructions
Answer these in your Casebook before you present
  1. Which location has the most extreme pH reading?
  2. Is it acidic or basic — and what does that mean for swimmer safety?
  3. What's your best guess at what's causing the problem at that location? (Think: what household or maintenance chemicals could match the pH you measured?)
  4. Which sample is closest to safe pool water (7.2–7.8)? Is any of them actually in the safe range?
  5. What should Wild Rivers do first — close a location, neutralize the water, or test for something more specific?
Discussion at your table:
  • Why would the wave pool's pH be different from plain tap water?
  • What might happen to pipes and pumps if water is too acidic or too basic for too long?
  • If you were the maintenance manager at Wild Rivers, which sample would scare you the most — and why?
🔢 The Math — pH Is a Log Scale

You've identified your suspect locations. Now make the science case airtight with the actual numbers — the math is what turns "this sample seemed bad" into "this sample is 10,000 times more acidic than safe water."

Here's the trick most people miss: the pH scale isn't linear. It's logarithmic.

That means each step on the scale is 10 times stronger than the step before it.

pH 6 is 10× more acidic than pH 7
pH 5 is 100× more acidic than pH 7
pH 4 is 1,000× more acidic than pH 7
pH 3 is 10,000× more acidic than pH 7

Same idea on the basic side. pH 11 is 10,000 times more basic than pH 7.

Instructions
Part I: Compare your worst sample to safe water

Find the sample with the most extreme pH (farthest from 7). Calculate how many times more acidic or basic it is than the Pacific Grille drinking fountain sample (your safe baseline).

Example: if your worst sample reads pH 3 and the fountain reads pH 7, the difference is 4 steps. 10 × 10 × 10 × 10 = 10,000 times more acidic.

Record this calculation in your 📋 Water Mystery handout. This number is the evidence that makes your report stick.

Instructions
Part II: Why this matters in the real world

Pool water for swimming is supposed to stay between pH 7.2 and 7.8. That's a tight window.

  • Below pH 7 → water can corrode metal pumps and irritate eyes/skin.
  • Above pH 8 → chlorine stops working properly and bacteria can grow.
  • A pH difference of even 1 full point is a 10× change in acidity. That's why pool maintenance is constant.
📣 Detective's Report

Each team has 2 minutes to present. Bring your 📋 Water Mystery handout — your data is your evidence.

Be ready to answer:
  1. Which location is most dangerous — and what is its pH?
  2. How does it compare to safe water? Use the log-scale math.
  3. What do you think is causing it? What evidence supports your guess?
  4. What should Wild Rivers do next?
🎓 Career Connection

What you did today — testing unknown water samples to determine if they're safe — is exactly how water quality is monitored at every public pool, river, drinking water plant, and hospital lab in the country.

Real Jobs
Where pH testing leads
  • Water quality chemist — tests rivers, lakes, swimming pools, and tap water for pH, bacteria, and contaminants. Most cities have one.
  • Environmental engineer — designs systems that keep water safe at scale: treatment plants, pool filtration, industrial runoff control.
  • Pool / aquatics operator — runs the chemistry on every commercial pool. Required certification, not a 4-year degree. Wild Rivers has a whole team of these on staff.
  • Forensic chemist — identifies unknown liquids at crime scenes or accident sites. Cabbage juice is a toy version of what they do with mass spectrometers.
  • Public health inspector — visits restaurants, pools, and water systems and checks chemistry against safety codes.
  • Marine biologist — pH testing is core to studying ocean acidification, coral reefs, and aquatic ecosystems.

Path note: Pool operator certification can be earned at a community college in a few weekends. Water quality chemist usually needs a chemistry or environmental science bachelor's. The pH skill is the same — the credentials just change what you're allowed to test.

💭 One Word

Before you leave, share one word that describes today. Just one.

Case closed. You diagnosed six unknown water samples, did real chemistry math with the log scale, and made an evidence-based recommendation. Forensic chemists do exactly that every day — just with bigger machines.

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