Lesson 43

Card 5.8: Ocean Acidification

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Format: Demo experiment + short seminar

Time: 40 min

Prerequisites: None

Core Question

A third of the carbon dioxide we emit dissolves into the sea, and dissolved carbon dioxide is a weak acid. What does slowly acidifying an ocean do, and how would you even measure it?

Resource (~10 min)

The chemistry in three steps: carbon dioxide plus water makes carbonic acid; acid lowers pH; lower pH steals the carbonate that shells and corals are built from.
The measurement connection: pH sensing platforms include, yes, Argo-family floats.

Activity: The Shell Race

Three cups: plain water, vinegar solution (exaggerated acid), and carbonated water (the honest analog: acidified by dissolved carbon dioxide alone). A piece of chalk or shell fragment in each. Observe over the class period and again next class; record what each looks like and any bubbling. Write the caveat sentence yourself: how is the vinegar cup misleading about the real ocean, and why is the carbonated cup the fairer comparison?

Clearing This Card

Observation log with the caveat sentence, plus a 90-second oral check: “Walk me from a car’s tailpipe to a thinner oyster shell, step by step.”

If You Miss This Class

Cups are trivially reproducible during studio time; same log and check.

Why This Matters

Acidification is the kind of ocean-change story behind mission themes year after year, and it connects the float’s sensor payload to a global measurement problem. Also, the caveat sentence is real science practice: knowing what your demo exaggerates is knowing what your data means.