Week 2 A&P Lab & Inquiry: Measuring Acidity

Human Anatomy and Physiology I Free sample edition

Part 1 — The Big Picture

This week you learned that pH counts hydrogen ions on an inverse scale, that a lower number means more acid, and that each whole step is a tenfold change. You also learned that your blood is held between 7.35 and 7.45, with acidosis below and alkalosis above. In this lab you measure six liquids in a free pH simulation, sort each one as an acid, neutral, or a base, watch what happens to an acid's reading as you add water, and turn two of your readings into a fold-change by counting the steps and then raising ten. Then you check a chatbot's account of your lab and catch where it reads the scale backward, drops a step, flips a label, or invents a number.

Time budget: Plan for about 120 minutes.

Part 2 — The Task

Guiding question: How acidic or basic are six liquids, how many times more hydrogen ions does one carry than another, and which way does an acid's pH move when you add water?

Before you begin — hypothesis: Before you add any water, write your hypothesis about dilution in the if… then… because… form: if water is added to one of your acidic liquids, then its pH reading will move in a direction you name, because of a reason about hydrogen ions you can state. Then write the prediction your hypothesis makes for the reading after two additions of water.

Workshop data: Your own six pH readings from the PhET pH Scale simulation, or the lab's illustrative fallback readings

Source: pH readings you take yourself in the free PhET pH Scale simulation with the procedure in Part 3; if you cannot run the simulation, use the illustrative fallback readings printed in Part 3, which were constructed for this lab and are not real measurements of any product.

Rows: 6 liquids, one reading each, shown as 6 rows of the reading table; the first scaffold table has 4 rows for the parts of the test, the dilution table adds 3 rows for one acid before and after water is added, and the fold-change table has 2 rows
Scale: pH readings fall on the 0 to 14 scale, with 7 neutral

Part 3 — Materials & Procedure

Tools and materials

A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet)
A document, notebook, or spreadsheet for your tables and answers

Ways of working

structure-identification-on-a-virtual-atlas
histology-on-a-virtual-microscope
at-home-physiology-measurement-and-data-table

Procedure

Open the free PhET pH Scale simulation in a web browser and choose the screen that shows a beaker of liquid with a pH probe. Before measuring, write your dilution hypothesis and prediction in the first table, and define the variable so it can be measured: the pH reading, read from the probe and rounded to the nearest whole number. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: The simulation is open with a liquid in the beaker, and your hypothesis is written before any water is added.
Pick a liquid from the simulation's list, place the pH probe in the liquid, and wait for the reading to settle. Write the liquid's name and its reading in the reading table, then round the reading to the nearest whole number in the next column. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: One row of the reading table holds a liquid's name, its reading, and the rounded value.
Repeat step 2 until you have six different liquids. Then sort each one: below 7 is an acid, exactly 7 is neutral, above 7 is a base. Mark the liquid that carries the most hydrogen ions. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Six rows, each with a reading and a class, and one liquid marked as carrying the most hydrogen ions (the lowest reading).
Choose one acidic liquid. Record its reading in the dilution table, then use the simulation's water control to add water twice, recording the reading after each addition. Compare what happened with your prediction. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Three readings for the same liquid, before and after two additions of water, and a sentence on whether your prediction held.
Choose two of your six liquids whose rounded readings are different. In the fold-change table, count the whole-unit steps between the two rounded readings out loud, then raise ten to that power, writing the multiplication in full. Work the practice pair the same way. If you like, check the power of ten in a spreadsheet cell, where =10^3 returns 1000. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Two fold-changes, each with the counted steps, the multiplication written out, and the result said in words.
Answer the analysis questions, then run the AI-critique step in Part 6 or the equivalent route, and assemble everything listed in Part 7. Tool: A free virtual anatomy atlas or 3D anatomy viewer (Innerbody, GetBodySmart), a virtual microscope for histology (Histology Guide), free physiology simulations (PhET pH Scale, Membrane Channels, Neuron, Gene Expression Essentials), and a spreadsheet (Google Sheets or any free spreadsheet). Check: Every table is complete, the five questions are answered, and the critique or the marked-up flawed analysis is ready to submit.

Fallback route

When to use it: Use this route if you cannot open the PhET pH Scale simulation, or if it will not run on your device.

Use the illustrative fallback readings below, constructed for this lab and not real measurements, as your reading table and dilution table, then complete every scaffold table, analysis question, and the critique step from them and submit the same items for equal credit.

This route earns the same credit as the primary route.

Illustrative fallback readings, constructed for this lab, that stand in for your own six liquids and your dilution test.

Fallback model data
Liquid	pH reading	Rounded to a whole number
Liquid A	2	2
Liquid B	3	3
Liquid C	6	6
Liquid D	7	7
Liquid E	9	9
Liquid F	11	11
Liquid B after the first addition of water	4	4
Liquid B after the second addition of water	5	5

Part 4 — The Scaffold

Name your hypothesis and your measured variable before you add any water, so the test is fair from the first reading.

Student scaffold table 1
Part of the test	Your answer
Hypothesis about adding water to an acid (if… then… because…)
Prediction for the reading after two additions of water
The variable you measure, defined so it can be measured
What you keep the same between readings

Record each liquid's reading as soon as it settles, round it, then sort it against 7.

Student scaffold table 2
Liquid	pH reading	Rounded to a whole number	Class (acid, neutral, or base)
1
2
3
4
5
6

Follow one acid's reading as water is added, so you can test your prediction against what happened.

Student scaffold table 3
Moment	pH reading	Direction compared with the reading before
Before adding water		(starting value)
After the first addition of water
After the second addition of water

Turn two readings into a fold-change by counting steps first and raising ten second, with every step written out.

Student scaffold table 4
Pair	Lower rounded reading	Higher rounded reading	Whole-unit steps counted	Ten raised to that power, multiplied out	The result in words
Your own pair
Practice pair: Liquid E (illustrative pH 9) and Liquid F (illustrative pH 11)	9	11

Part 5 — Analysis Questions

Using the fold-change table, write out both comparisons in full: the steps counted one at a time, the multiplication by ten at each step, and the result in words. Which liquid in each pair carries more hydrogen ions, and how do you know from its number alone?
Describe how the acid's reading changed as you added water. Did it move toward 7 or away from it, and did that match your prediction? Explain the change in terms of hydrogen ions.
Your blood is held between 7.35 and 7.45. Suppose an illustrative reading of 7.0 appeared on a chart. Name the side of the range it falls on, and explain why a drop of a fraction of a unit is still a meaningful rise in hydrogen ions.
Connect this lab to the body: put the chain for a hard stair climb in order (working muscle, carbon dioxide, carbonic acid, buffers and breathing), and explain what a buffer does that plain water in your beaker did not do.
Choose one of these two reflection options and answer it in 3–4 sentences: (a) rounding a reading to a whole number is a source of error; name one way it could change a fold-change you computed, and one way to report the result more honestly; or (b) a simulation is a model, not a body; name one thing your simulated readings can tell you about blood pH and one thing they cannot.

Part 6 — AI-Critique Moment

Choose one equal-credit critique route. Route A: ask an approved AI tool to critique your completed work, then check its response against your own evidence. Route B is the no-AI equivalent printed below.

Approved tools: Claude, Gemini, ChatGPT, Grok, Microsoft Copilot.

Prompt to paste:

I've pasted my completed Measuring Acidity tables above. They come from the free PhET pH Scale simulation, or from the lab's illustrative fallback readings: Liquid A reads pH 2, Liquid B pH 3, Liquid C pH 6, Liquid D pH 7, Liquid E pH 9, and Liquid F pH 11. Please do six things, showing your reasoning. First, sort each liquid as an acid, neutral, or a base, and say which one carries the most hydrogen ions. Second, compare Liquid A with Liquid D: count the whole-unit pH steps between them and say how many times more hydrogen ions Liquid A carries. Third, describe one water molecule in words, saying which atom carries the slight negative charge and which carry the slight positive charge. Fourth, name which of water's four jobs in the body (solvent, heat sink, lubricant, reactant) explains salt coming apart in blood plasma. Fifth, put these events in order for a hard stair climb: buffers and breathing respond; working muscle makes carbon dioxide; carbon dioxide makes carbonic acid. Sixth, tell me whether a blood pH above 7.45 is acidosis or alkalosis, and tell me what share of an adult's body mass water can make up.

Test the response for these likely failures:

Chatbots often drop a step or subtract the two readings, reporting Liquid A (pH 2) versus Liquid D (pH 7) as 5 times or 10,000 times more hydrogen ions.
Chatbots sometimes read the scale in the wrong direction, calling the liquid with the highest reading, Liquid F, the most acidic, or calling a blood pH above 7.45 acidosis.
Chatbots sometimes flip the partial charges on water, labeling the oxygen δ+ and each hydrogen δ−.
Chatbots sometimes pair salt coming apart in plasma with water's heat-sink or lubricant job.
Chatbots sometimes start the chain with breathing or with carbonic acid, putting the response before the cause.
Chatbots often state an exact, confident share of body water, such as 70% or 75%, or cite a study that was never given.

Write 3–4 sentences: name at least one thing the chatbot got right, quote at least two of its errors, and correct each one with the step count, the charge label, the job name, the order, or the course figure that fixes it.

Equivalent route (no AI required)

No AI account is needed for this lab. Instead of the chatbot, critique this flawed analysis, printed here in full: "Liquid F at pH 11 is the most acidic of my six liquids because it has the highest number. Liquid A at pH 2 has 10,000 times more hydrogen ions than Liquid D at pH 7. In a water molecule the oxygen is δ+ and each hydrogen is δ−. Salt comes apart in blood plasma because water works as a heat sink. On a stair climb, breathing speeds up first, then carbonic acid forms, and then the muscles make carbon dioxide. A blood pH above 7.45 is acidosis. Water makes up 75% of every adult's body mass, according to a study." Mark every error you find, write the correction beside it using this week's rules, and add 3–4 sentences on which error you think a student is most likely to miss and why. This route assesses the same objectives as the chatbot critique, Objective 2 (relate the chemistry of the body to its function — atoms and the three bond types, water's properties, the logarithmic pH scale with the blood's buffered range, and the four classes of organic compounds — and explain the cell's membrane, organelles, and transport (diffusion, osmosis and tonicity, active transport, and bulk transport), the overview of how a cell makes ATP, and how a gene is read into a protein) and Objective 1 (use the language of the body correctly — the anatomical position, the directional-term pairs, the three body planes, and the body cavities and abdominal regions — distinguish anatomy from physiology, climb the levels of structural organization, list the functions and requirements of human life, and trace a homeostatic feedback loop through its receptor, control center, and effector, telling negative feedback from positive feedback), takes comparable effort of about 20 minutes, is scored by the same row of the scoring criteria for the same credit, and its submission artifact is your marked-up flawed analysis with your corrections and sentences, uploaded with the rest of your report.

Part 7 — What to Submit

All four completed scaffold tables, filled from your own simulation readings or the illustrative fallback readings
Written answers to all five analysis questions
The chatbot critique report with its share link, or the equivalent route's marked-up flawed analysis

Deliverable:

A short A&P Lab & Inquiry report on measuring acidity: four completed tables (the parts of the test, six readings with classes, the dilution readings, and the fold-change comparisons), written answers to five analysis questions, and a critique of a chatbot's account of your lab, or, on the equivalent route, a marked-up correction of the printed flawed analysis. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text. Choose a written, recorded, or visual form for your answers; every form is graded by the same scoring criteria.

Rubric

The rubric below shows how each submitted part is evaluated; bands are full, partial, or none.

Workshop evaluation criteria
Criterion	Full	Partial	None
Testable hypothesis and a measurable variable	A falsifiable if… then… because… hypothesis about dilution and a prediction appear before any water is added, and the measured variable and what stays the same are both named.	A hypothesis appears but names no direction or reason, or the measured variable or what stays the same is missing.	No hypothesis, and no variable named.
Reading table and classification	Six readings are recorded from the simulation or the fallback readings, each is rounded and sorted correctly against 7, and the liquid with the most hydrogen ions is the one with the lowest reading.	Most readings are recorded and sorted, but one or two classes are wrong, or the most-hydrogen-ion liquid is read from the wrong end of the scale.	Readings are missing, or invented, or the classes are not given.
Fold-change and dilution arithmetic	Both fold-changes count the whole-unit steps before raising ten, with each multiplication written out and the result said in words, and the dilution readings are recorded with the direction of change named.	One fold-change is worked correctly, or both are set up correctly with one slip, or the dilution direction is named without the readings.	No fold-change, or the pH values are subtracted to give a fold, and no dilution readings.
Analysis in words	The answers name the side of the blood's range a 7.0 reading falls on, order the stair-climb chain correctly, explain what a buffer adds, and give a limitation of the lab's readings.	Two or three of those four pieces are present and accurate.	One or none of those pieces is present, or the side of the range or the chain order is wrong throughout.
AI-critique or equivalent route	The chatbot report, or the marked-up flawed analysis on the equivalent route, quotes at least two specific errors and corrects each with the course's rule; both routes earn the same credit.	One error is quoted and corrected, or errors are named without a correction, on either route.	No critique on either route, or model output is pasted without any check.

Quality Gate

Every reading in the tables comes from your own simulation run or the printed illustrative fallback readings, never from memory or a chatbot.
Every fold-change counts the whole-unit steps before raising ten, and no two pH values are subtracted to give a fold.
The hypothesis was written before any water was added and has the if… then… because… form.
The measured variable is defined so it can be measured, and what stays the same between readings is named.
No pH value for a product, measurement, study, or source is invented anywhere in the submission.
The critique quotes the chatbot or the flawed analysis and corrects at least two errors with the course's rules.

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