Acid Boy & Base Girl: The pH Game
7 min read
Acid Boy can stand in lemon juice. Put Base Girl on it and she starts to dissolve.
Short answer: Acid Boy & Base Girl is our 3D puzzle platformer about acids and bases. You guide two heroes through a laboratory where most platforms are everyday substances with a real pH. Acid Boy is safe below 7, Base Girl above 7, both at 7. The first two missions are free in a browser.
To get through a room, you read the pH of each substance and send the hero who can stand on it.
How do you play the pH game?
We built Acid Boy & Base Girl around a fictional safety rule about pH. In the game’s aqueous model at 25 °C, the pH scale is 0 to 14, and it is along the bottom of the screen the whole time. Everything below 7 is acidic, everything above 7 is basic, and 7 is neutral. Acid Boy is safe on acidic ground and neutral pads. Base Girl is safe on basic ground and neutral pads.
You control both heroes and switch between them with Q. Each room has sample tiles set in solutions, each marked with a ? until a hero tests it, and only the hero who can survive standing in it can test it. In the first mission that means Acid Boy takes the lemon juice (pH 2) and Base Girl takes the soap solution (pH 10). Then there's a limestone wall in front of the door. Two bottles are on the start pad, vinegar and soap solution, and only one of them dissolves limestone.
Send the wrong hero and they start to lose health, fast. The screen flushes red, and over the hero's head you see the substance, its pH, and a warning that Base Girl needs to get off the lemon juice. You retry from the last checkpoint, so a wrong guess costs a few seconds.
What do you learn in each mission?
We built each of the nine missions in Acid Boy & Base Girl around one idea about acids and bases, and each idea depends on the one before it. Missions 3 and 5 have taller rooms with lifts and pressure plates, and mission 4's puzzle is on two floors. In the workshop of mission 6, every bottle a hero needs is on the other hero's road at the start. In mission 7 you build a staircase of beakers, one tenfold dilution at a time. The chemistry is at the level of a first-year high school course throughout.
| Mission | Room | What you learn by playing | Access |
|---|---|---|---|
| 1. The limestone door | Reaction Lab | Acids are below 7 on the pH scale, bases above 7, neutral at 7; an acid dissolves limestone | Free |
| 2. Crossed wires | Reaction Lab | Choose routes by pH, then pair equal amounts of H⁺ and OH⁻ to make water | Free |
| 3. Just enough | The Titration Terrace | Partial neutralization, balance, and excess are three different results | Full access |
| 4. Six Bottles, No Labels | Unlabeled Gallery | Sort six bottles by evidence: a limestone fizz test, indicator strips, and a lamp for checking three at a time | Full access |
| 5. Pack more into a dose | Concentration Falls | Concentration is amount per volume, so equal volumes can hold different amounts | Full access |
| 6. Acids and bases at work | The Repair Bay | Match each job to its chemistry: an acid for limestone and a lye spill, a mild base for an acid spill, and a strong base for grease | Full access |
| 7. Read the scale carefully | The Dilution Cellar | Each pH step is a tenfold change: dilution climbs toward 7 one step per tenfold and never reaches it | Full access |
| 8. Restore the lab | The Glasshouse | Test guessed labels and correct them with proof — and a balanced mixture is not always pH 7 | Full access |
| 9. Count the amounts | The Counting House | Count reacting amounts in mmol, not doses: equal volumes can react differently, and sulfuric acid supplies two H⁺ each | Full access |
Mission 2 has forks in the route. There are two, and we put a different hero's substance on the high road at each: at the first fork baking soda (pH 9) is above vinegar (pH 3), and at the second rainwater is above soap (pH 10). The rainwater's sensor is offline, so you decide whose tile it is: carbon dioxide from the air makes rain slightly acidic, about pH 5.6.
At the end of that room is a reactor with a model hydrochloric acid solution in it. Before you touch it, you get a short lesson: one worked example of H⁺ and OH⁻ pairing into water, a second case where you predict which ion will be left over, and then the same problem in reverse. Then you dose the game’s reactor yourself. When the amounts are equal, the sensor's reading is pH 7 and you can activate the bridge across the gap.
Is it like Fireboy and Watergirl?
Acid Boy & Base Girl has one idea in common with Fireboy and Watergirl, the browser platformer Oslo Albet released in 2009 with The Forest Temple: two heroes, each safe on a different kind of ground, who have to help each other through a level. Acids and bases are the same kind of pair, and our art direction lists Fireboy and Watergirl as a reference.
Two things are different. First, the hazards are real substances with real pH values, and you need to know them to finish a room. Second, the puzzles are about amounts as well as colors: by mission 5 you are comparing two bottles of the same volume and different concentration.
If you came here looking for games like Fireboy and Watergirl, this one has the same two-hero coordination, and you can play it with a friend: with full access you send the link, your friend joins free, and each of you takes one hero on your own device. The hazards are lemon juice, vinegar, soap, and lye instead of fire and water.
Why build a chemistry video game this carefully?
Students compare Acid Boy & Base Girl with the games on their phones and consoles, so those are the games we measure it against. Our design standard lists Team Asobi's Astro Bot as the reference for character appeal and animation, and the lab, the heroes, and the machinery are original 3D models we made for this game. Cobalt, element 27 and our in-house guide, opens each mission with a short briefing you can skip and gives hints when you ask for them. We hold every game on Periodic Mole, from Bond Forge to Storm the Castle, to that same written standard.
There's a teaching reason for that effort. In many learning games, including our own Bond Forge, the chemistry is in a question card and the game is the reward for answering it. That design is a good fit for facts like element symbols, which is why we used it in Bond Forge. Acids and bases are a different kind of knowledge: a relationship between numbers, substances, and amounts. In this game we laid out each level from the pH values, so you use them every time you choose a route.
We built the reactor lesson in mission 2 (a worked example, a prediction, then your own attempt) on the U.S. Institute of Education Sciences practice guide on organizing instruction (Pashler and colleagues, 2007), in which the authors recommend pairing graphics with explanation and alternating worked examples with attempts.
We built it as a three-dimensional Reaction Lab, with animated heroes, labeled substances, and machinery you operate. The first two missions are free, so start mission 1 and judge that for yourself in about five minutes.
Is the chemistry in the game accurate?
We built Acid Boy & Base Girl on a model of dilute aqueous solutions at 25 °C, and the game has a field notebook that lists which parts are real chemistry and which are game fiction. Open it from the flask icon in any room. A few lines from it:
- "Strong and weak describe ionization. Concentrated and dilute describe amount per volume. A pH reading alone does not tell you acid strength."
- "pH values do not average when solutions mix."
- "Other acid–base reactions can finish above or below pH 7 at equivalence."
- "Character immunity, dissolving, healing, bubbles, and solid bridges are game fiction."
Household pH values in the game are representative samples. Real lemon juice and real soap vary by brand and concentration, and we say so in the notebook. The mixing stations have only model hydrochloric acid (HCl) and sodium hydroxide (NaOH), a strong acid and a strong base, which is the case where a mix of equal amounts is exactly pH 7. We list typical pH values for everyday substances, with their sources, in Acids, Bases, and pH: A High School Guide.
The game and a simulation are a good pair. In PhET's pH Scale from the University of Colorado Boulder, you dip a probe into coffee, soap, and spit and watch the reading change as you dilute. Use the simulation to experiment freely and the game to practice the same ideas against a goal.
Who is Acid Boy & Base Girl for?
We built Acid Boy & Base Girl for high school students meeting acids and bases for the first time, including students who haven't learned ions or moles yet. We introduce each term beside its symbol the first time you need it.
- Students: play mission 1 before your class starts the acids and bases unit. You'll start the unit already knowing where lemon juice, vinegar, and soap are on the pH scale. If you'd rather have the lesson first, we teach acids, bases, and pH from the first idea in our free pH module, with no account needed, and when you finish it we send you to missions 1 and 2.
- Parents: you need no account and no card for the free missions. A mission is a few minutes long, and the par time for the first one is 75 seconds.
- Teachers: students can play in a browser on a Chromebook or laptop, with touch controls on tablets. It is a warm-up before a pH lab or a check afterward: in mission 4, students sort six bottles with no pH on them, from cola to ammonia, with a fizz test and indicator strips.
Try it free. Bond Forge is free to play with a starter set of elements, no account needed. Full access is $59 for a year: every game and all 118 elements, with progress saved. No subscription.
The rest of the collection, from element games to a chemistry siege game, is on the games page.
FAQ
Is Acid Boy & Base Girl free? The first two missions are free to play in a browser, with no account needed. The later missions, and saved progress, are part of full access: $59 for one year or $79 for two, with a 30-day refund.
Can two people play Acid Boy & Base Girl together? Yes. The player who sends the link needs a Periodic Mole account, and full access for the later missions. Pick a mission, press Play with a friend, and send the link. You play one hero and your friend plays the other, each on a separate device. Your friend joins free, without an account.
Do I need to know chemistry to play? No. You learn the pH scale in the first mission as you play, and the reactor in mission 2 has a short lesson you can replay any time. We built the game for students before or during their first chemistry course.
What device do I need? A browser. You can play Acid Boy & Base Girl on laptops and Chromebooks with a keyboard, and on tablets and phones with touch controls. You need a device with 3D graphics. There's nothing to install.
Is there an acid base game for high school? Acid Boy & Base Girl is an acid base game we built for high school: nine missions on the pH scale, neutralization, excess, reading substances without an indicator, concentration, matching acids and bases to cleanup jobs, tenfold dilution, checking guessed labels, and counting reacting amounts. For free-form experimenting, PhET's pH Scale simulation is a good companion.
Sources
- Fireboy and Watergirl, Wikipedia: Oslo Albet, The Forest Temple, 2009.
- PhET Interactive Simulations, University of Colorado Boulder, pH Scale.
- Pashler, H., et al. (2007). Organizing Instruction and Study to Improve Student Learning. Institute of Education Sciences, U.S. Department of Education.