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Module

Acids, bases, and pH

Before you start

Here’s the plan

In these lessons, you'll learn to answer the six kinds of acid and base questions New York has put on the new Physical Science: Chemistry exam so far, and one more kind on New York's list of what the course covers.

We wrote this for the new Regents exam, Physical Science: Chemistry, and its 2025 Reference Tables, the pages of charts and data you get to use during the exam. On the June and August 2026 exams, 10 of the 98 questions were about acids, bases, and pH, about one question in ten. The 2025 Reference Tables have no acid, base, or indicator table and no pH formula, so you need to know what pH means without looking it up. On the exams it has released, New York printed an indicator chart beside every question about indicators.

Questions you’ll learn to answer

  • In a reaction, which substance is the acid and which is the base?
  • How do you compare the hydronium ion concentration, [H₃O⁺], of two solutions from their pH values?
  • Is a solution with a given pH acidic, basic, or neutral?
  • What can an indicator's color tell you about a solution's pH?
  • When you add or remove one of the substances in an equilibrium that involves H₃O⁺, which way does it shift, and what happens to the pH?
  • How could you raise or lower the pH of something real, like the water that plants grow in when there's no soil?
  • When a strong base has reacted with all of a weak acid, is the pH below 7, at 7, or above 7?

How it goes

  1. First, you can take a short check on what you already know. You’ll answer at most 16 questions. Answering all 16 takes about 6 to 8 minutes, and we may stop sooner. After the lessons, we ask less often in review about anything your answers cover.
  2. Then you’ll work through 6 short lessons. After each one, we ask you one question. In 3 of them, you’ll see a worked example before the question. Allow about 25 to 35 minutes for all of them; you can stop after any lesson and pick up there later.
  3. In missions 1 and 2 of Acid Boy & Base Girl, our acids-and-bases game, you put acids and bases to work: you dissolve a limestone wall and balance a reactor.
  4. After the lessons, we ask you the module’s 21 questions: the ones you’ve answered and the ones that are new to you. You can start your first review right after the lessons. On later days, we ask you at most 20 that are due for review, plus the ones you’re still learning or haven’t seen yet. Answering 20 takes about 8 to 10 minutes, longer when you stop to read why an answer missed. You finish the module when you’ve shown on later days that you know all 21 and worked one exam-style cluster.
  5. Once you finish the lessons, you can work an exam-style cluster: a few questions about one set of data, then a written answer. It takes about 10 to 15 minutes.

Words you’ll meet