The Great Water Park Chemical Mystery
Riptide Ridge Water Park opens this weekend, but something is wrong with the water. At a few of the features, guests are climbing out with stinging eyes and itchy skin. At other features, everything seems fine. The park crew tested the water, got results they could not explain, and called in a team of young chemists: you.
Six features are under investigation. Somewhere in this park, the water chemistry has gone off. Your job is to find where, figure out how bad it is, and tell the park what to do.
Before you test anything, know what you are measuring. pH is a number from 0 to 14 that tells you how acidic or basic a liquid is.
0 to 6
7
8 to 14
An indicator is anything that changes color to show where a liquid falls on the pH scale. Today you use two: pH test strips and red cabbage juice.
You will match every color you see to the two charts on your handout: chart 1 for the strips, chart 2 for the cabbage juice.
The park just hired your team. Work like real investigators: observe carefully, record what you notice, talk with your partner, and use evidence before you make a claim.
There are six sample stations, one for each feature. Your group fills one numbered tube per station.
Add 5 to 6 mL from each station into the tube with the matching number. Carry your tubes back to your workspace carefully.
Tube number must match station number. Each sample stays in its own tube. Never pour one sample into another. If your numbers get mixed up, your whole case falls apart.
These are pretend water park samples, but treat them like real lab chemicals. Do not taste or smell them, and keep them away from your face. If a sample gets on your skin, rinse with water and tell your teacher.
First reading: the pH strips. Chart 1 on your handout is your key. This is round one, so do not touch the cabbage juice yet.
Dip a fresh pH strip into tube 1. Wait a few seconds, then match its color to chart 1 on your handout. Write the number in the pH Test Strip Result column. Use a new strip for every tube. Never reuse a strip.
As you finish each strip, lay it on the table in order, 1 through 6, next to your handout. Now your whole team can see all six results side by side.
Which samples read below 7 (acidic)? Which read above 7 (basic)? Which one is closest to 7? Fill in the last column of your handout: does each sample look Normal or a Problem?
As every group wraps up their strips, watch this. It breaks down what the pH number actually means, so you are ready to talk through your six results as a class.
Stop here. Do not make your cabbage indicator yet. Finish all six strips, fill in the pH Test Strip Result and the "What does this suggest" column, and wait for your teacher. The whole class discusses the strip results and tests with cabbage juice together.
Round two uses red cabbage juice, a natural indicator you make yourself. It will give you a second reading to compare against your strips.
Put 1/4 cup of chopped red cabbage into your baggie. Add just enough water to cover the cabbage, no more. Seal the bag tightly and press the extra air out.
Squeeze and massage the bag for several minutes, passing it around so everyone in your group takes a turn. Keep going until the water turns deep purple. The darker it gets, the stronger your indicator.
Stretch the cheesecloth over your cup and hold it in place with the rubber band. Slowly pour the purple liquid through the cloth into the cup. That purple juice is your indicator. Keep the cup for step 7.
Red cabbage contains a pigment called anthocyanin. Acids and bases change the shape of that molecule, and a different shape reflects a different color. That is why one liquid turns it one color and another turns it a different color.
Now use your indicator on every sample. Chart 2 on your handout is your key.
Add 2 mL of cabbage juice to each tube, one at a time. Watch the color change. Record the observed color in the Observed Color column, then use chart 2 on your handout to decide what that color means.
You now have two clues for each sample: the pH strip and the cabbage color. If they point the same way, that is strong evidence. If they disagree, trust the pH strip and make a note of it.
Lay your six rows side by side and compare. You are hunting for the sample that stands out the most.
The sample with the most extreme pH is the feature in the most trouble. That is the one your team investigates in Part 2.
Turn to Part 2 on your handout. Use your evidence, not a guess, to answer with your team.
Which sample has the most extreme pH reading?
Acidic or basic, and what does that mean for the water park?
What could be causing the problem at that source? Think about what might drip, leak, or wash into that one feature.
What should the water park team do next to protect the affected area?
Getting water back toward the safe middle is called neutralizing. If a sample is too acidic, adding a base moves it toward neutral. If it is too basic, adding an acid moves it toward neutral. Which one does your suspect need?
You made your own indicator, tested six samples two different ways, and built a case from real evidence. That is exactly how chemists keep water, food, and people safe. Great work, investigators.