Week 2 — A&P Lab / Scientific Inquiry · "Measuring Acidity"

Course: Anatomy & Physiology I (BIOL 2301 + BIOL 2101) · Silver Oak University (fictional sample) · Prof. Navarro
Objective: Objective 2 — pH, acids/bases & buffers (quantitative); the chemistry of homeostasis · SLO A (homeostasis — pH balance) · SLO B (quantitative physiology — the pH fold-change arithmetic)
Worth 50 points · Labs group = 15% of the grade · Lab 2
Format: a guided exploration of a free virtual chemistry simulation (no download, nothing to buy) — you'll measure the pH of liquids, dilute them and predict the result, record how many times more acidic one solution is than another, and then catch the AI's pH-math mistakes.

This is the course's signature weekly component. Every instructional week has one A&P lab. This week's uses a free PhET physiology/chemistry simulation; later weeks add a virtual microscope (histology) and the virtual anatomy atlas. All lab resources are links to external sites — nothing to buy or download. This is a quantitative-pocket week, so bring a calculator.

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Part 1 — The Big Picture

This week you learned the pH scale, the rule that each whole pH unit = a 10× change in H⁺, and how buffers defend your blood near pH 7.4. Today you'll measure pH yourself on a virtual instrument, dilute solutions and watch H⁺ change, and compute fold-changes the right way — counting units, then multiplying by 10. This is the exact arithmetic that a confident chatbot gets wrong, so it's also where you practice catching it.

The scientific habit this builds: measure → record → compute → check the computation against a rule. In physiology, "how acidic" is a number, and getting that number right matters — for a blood gas, a urine pH, a drug dose. The lab is where the pH math becomes automatic.

Background (optional, ~5 min): OpenStax A&P §2.4, "Inorganic Compounds Essential to Human Functioning" — keep it open as your reference for the pH scale, acids/bases, and buffers: 🔗 https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning

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Part 2 — Your Scientific Question & Hypothesis

Chemistry labs start like any inquiry — with a question and a prediction you'll test against evidence (here, the simulation).

The question: When you compare two solutions by pH, can you correctly state how many times more acidic one is than the other — and predict what happens to pH when you dilute an acid?

Before you start, write your hypothesis / prediction:

I predict that diluting an acid with water will move its pH __ (toward 7 / away from 7), and that when I ask an AI to compute "how many times more acidic" one pH is than another, it will make at least ____ arithmetic error(s) I can catch.

(There's no "right" number for the AI part — you're predicting how reliable the AI will be, then checking.)

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Part 3 — Materials & Procedure

You need (all free, in a browser):
- The PhET "pH Scale" simulation (free, no download): 🔗 https://phet.colorado.edu/en/simulations/ph-scale
- A calculator (or just multiply by 10 in your head).
- Optional second reference: OpenStax §2.4 (linked above).
- An approved chatbot (Gemini, Claude, or ChatGPT) for Part 6.

Procedure:
1. Open the pH Scale simulation. Use the macro screen: select a liquid (e.g., water, milk, coffee, orange juice, soda, hand soap, drain cleaner) and read its pH from the meter.
2. For the Part 4 table, record each liquid's pH and whether it is acidic / neutral / basic (acidic < 7, neutral = 7, basic > 7).
3. Switch to the My Solution (or the micro / dilution) view. Make an acidic solution, then add water to dilute it and watch the pH move toward 7. Record the before and after pH for one dilution.
4. For each comparison in the table, compute how many times more acidic the lower-pH solution is, using the rule: count the whole pH units between them, then multiply by 10 for each unit (10ⁿ). Do not subtract the pH values.

No specific sim access? Any free pH simulation or a real litmus/pH-strip kit works. The skill — measure pH, dilute, and compute fold-changes correctly — is identical.

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Part 4 — Data Tables (fill these in)

Table A — Measure & classify (read the pH from the sim). (Approximate pH values are fine — the sim's defaults are close to those below.)

Liquid	pH (from sim)	Acidic / Neutral / Basic?
Pure water	______	______
Milk	______	______
Black coffee	______	______
Orange juice	______	______
Hand soap	______	______
Drain cleaner	______	______

Table B — Compute the fold-change (count units, then ×10). Use these clean integer pH pairs.

Comparison	Whole units apart	"× more acidic" (10 ^ units)	Which is more acidic?
pH 4 vs pH 7	______	______	______
pH 5 vs pH 7	______	______	______
pH 2 vs pH 5	______	______	______

Table C — Dilution (use the sim's My Solution / dilution view).

Start pH	Add water (10× dilution, ×3 = 1000× more water)	Predicted end pH	End pH (from sim)	H⁺ change (× fewer)
pH 1 (strong acid)	dilute 10× three times	______	______	______

(Hint for the dilution row: each 10× dilution of a strong acid raises pH by about 1 unit and cuts H⁺ to 1/10. Three such dilutions ≈ 3 units.)

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Part 5 — Identify the Reasoning

Answer in a sentence each:
1. Why is it wrong to subtract the two pH numbers to find "how many times more acidic"? What's the correct method, and why does each unit count as ×10?
2. When you diluted the acid, which way did the pH move, and what happened to the H⁺ concentration? Connect this to "lower pH = more H⁺."
3. Your blood is buffered near pH 7.4. Using one comparison from Table B as a reference, explain in plain words why a blood pH of even 7.0 (vs 7.4) would be a serious problem — and name what that low-pH condition is called. (This is the homeostasis tie-in.)

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Part 6 — AI-Critique Moment (required — this is the BYOAI step)

Now bring in your approved chatbot (Gemini, Claude, or ChatGPT) and be the clinician who checks the math.

1. Paste this to the chatbot: "How many times more acidic is a solution at pH 4 than one at pH 7? And how many times more acidic is pH 5 than pH 7? Show your work."
2. Check everything it says against the rule (each unit = ×10):
   - Did it say 1000× for pH 4 vs pH 7 (3 units → 10 × 10 × 10)? Many chatbots answer "3 times" (subtracting) or "30 times" — both wrong.
   - Did it say 100× for pH 5 vs pH 7 (2 units → 10 × 10)? Watch for "2 times" or "20 times."
   - Did it keep the direction right (lower pH = more acidic = more H⁺)?
3. Write 2–3 sentences reporting what the AI got right and at least one arithmetic error you caught and corrected (with the correct number and the count-units-then-×10 method). If it happened to get everything right, say how you verified each answer with the rule — that's the skill.

The habit all term: the tool drafts, you judge. A chatbot will confidently subtract pH values and tell you pH 4 is "3 times" more acidic than pH 7 — it's 1000 times. Catching that is the point, and in the clinic a miscomputed concentration is not harmless.

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Part 7 — What to Submit

Submit a single document (or text entry) with: your hypothesis/prediction, your completed Part 4 tables (A, B, C), your Part 5 answers, and your Part 6 AI-critique paragraph. Due Sunday, Sep 13, 11:59 p.m. (50 points).

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Instructor answer key — REMOVE BEFORE PUBLISHING TO STUDENTS

Every pH value and fold-change below was pre-computed and independently re-verified in Python (each whole pH unit = a 10× change in H⁺; fold-change = 10^(units apart)). Table-A pH values are the sim's approximate defaults — accept reasonable readings.

Table A — approximate expected readings:

Liquid	pH (approx.)	Class
Pure water	7	neutral
Milk	~6.5	acidic
Black coffee	~5	acidic
Orange juice	~3.5	acidic
Hand soap	~10	basic
Drain cleaner	~13	basic

Table B — verified fold-changes:

Comparison	Units apart	× more acidic	More acidic
pH 4 vs pH 7	3	1000× (10³)	pH 4
pH 5 vs pH 7	2	100× (10²)	pH 5
pH 2 vs pH 5	3	1000× (10³)	pH 2

Table C — dilution (verified):

Start pH	Dilution	Predicted/observed end pH	H⁺ change
pH 1	10× three times (≈1000× more water)	≈ pH 4 (about +3 units)	1000× fewer H⁺ (10³)

• Part 5: (1) Subtracting is wrong because the scale is logarithmic — each whole unit is a ×10 change in H⁺, not a +1 change, so you count the units and raise 10 to that power (e.g., 3 units → 10³ = 1000×). (2) Diluting the acid moved pH up, toward 7, because adding water lowers the H⁺ concentration; fewer H⁺ = higher pH. (3) Blood is normally ~7.4; a blood pH of 7.0 is 0.4 unit lower — and since each whole unit is ×10, even this fraction means a meaningfully higher H⁺ load on every protein/enzyme tuned to 7.4; sustained, it's life-threatening. A pH below 7.35 is acidosis. (For scale, Table B shows that whole-unit drops are 10×, 100×, 1000× — pH is extremely sensitive, which is exactly why the body buffers it so tightly.)
• Part 6 (AI-critique): full credit for a specific catch — most commonly the AI subtracting to say pH 4 is "3 times" (or "30 times") more acidic than pH 7 when it is 1000×, or saying pH 5 is "2×"/"20×" when it is 100×. Full credit also if the student verified each answer with the count-units-then-×10 rule.

Grading rubric — 50 points

Criterion	Full	Partial	None
Hypothesis / prediction — a clear prediction about dilution direction and the AI's reliability (6)	6	3–4	0–2
Data tables (Part 4 A–C) — pH readings + classifications reasonable; fold-changes correct (1000×, 100×, 1000×); dilution row sound (18)	18	9–15	0–7
Reasoning (Part 5) — why subtracting is wrong + dilution/H⁺ logic + the blood-pH homeostasis point (14)	14	7–11	0–5
AI-critique (Part 6) — names a specific pH-math error caught and corrected with the right number + method (8)	8	4–6	0–3
Quantitative accuracy — every fold-change computed by counting units and multiplying by 10, not subtracting (4)	4	2	0–1

Quality gate (self-checked): every chemistry fact in the key is verified against standard references (OpenStax A&P §2.4) — lower pH = more H⁺ = more acidic; blood ~7.35–7.45; acidosis < 7.35; buffers resist pH change. Anatomy/chemistry-accuracy gate: PASS. Every number was pre-computed and independently re-verified with a Python script (each whole pH unit = 10×): pH 4 vs 7 = 3 units = 10³ = 1000×; pH 5 vs 7 = 2 units = 10² = 100×; pH 2 vs 5 = 3 units = 1000×; pH 1 diluted 10× three times ≈ pH 4 = 1000× fewer H⁺. All fold-changes in the data tables and key match the verified values. Quantitative gate: PASS.