HESI A2 Chemistry: Every Topic Tested (+ the Math)

Real talk before you study anything: HESI A2 chemistry is the section your program probably does not even require, so confirm that first. Stuck taking it anyway? Good news — it is intro chemistry, not a college semester of it. The only tricky part is the math buried in a few topics like the mole and stoichiometry. Pair those with your math prep, rank the rest by yield, and you can cover the whole thing in about a week.

What topics does the HESI A2 chemistry section cover?

HESI A2 chemistry is the section nursing programs ask for the least — most schools stick to the big four (math, reading, vocabulary, and grammar) and never go near it. Before you crack a textbook, check which sections your school actually requires. Not on the list? You just handed yourself your study hours back.

If you are stuck with it, it is introductory chemistry — roughly nine topics, from atomic structure to acids and bases. When required, the section is short: usually 25 questions in about 25 minutes, sometimes with a few unscored extras. Those numbers move by program, so confirm the current format on the official Elsevier HESI page rather than trusting a random blog. Same goes for the passing score — there is no universal one; most programs want 75% or better, and competitive ones want more. The reassuring part: this is intro chemistry. No organic mechanisms, and you usually will not memorize the periodic table, because when a question needs one, they give it to you.

High-yield chemistry topics, ranked

Not every topic carries the same weight, so do not study them like they do. Because the section is short (only 25 questions), every item counts more than it would on a 50-question test — so go after the high-yield material first and leave nuclear chemistry for last. Start with atomic structure and the periodic table: they are the base everything else sits on, and they lean on recall far more than math.

Two concept notes, because they trip people up more than they should. Bonding comes down to one question: does an atom hand off an electron or share it? Hand off, and it is an ionic bond, usually a metal plus a nonmetal, like table salt. Share, and it is covalent. Acids and bases are even simpler — anchor on the pH scale: under 7 is acidic, over 7 is basic, and 7 (dead center) is neutral, like pure water.

The math behind the chemistry

Some of chemistry really is math wearing a lab coat. The mole, stoichiometry, molarity, and pH all lean on the exact skills the math section tests — mainly ratios, unit conversions, and careful setup. If numbers are your weak spot, this is where you will bleed points, which is why you should study these topics in the same sitting as your HESI A2 math review, not off in a separate world. But do not spiral — plenty of test-takers say the practice tests looked scarier than the real section, which stays basic. You are doing setup, not advanced calculation.

One quick demystifier: the mole is just a counting word, like "dozen," only enormous. One mole is 6.022 × 10²³ of something — usually atoms or molecules. Chemists use it because atoms are far too tiny to count one at a time, so the mole links the grams you can weigh to the particles you cannot see. Once that clicks, most stoichiometry is just careful bookkeeping.

The stoichiometry workflow

Most stoichiometry problems walk the same path. Drill it once and it stops feeling like guesswork.

1. Balance the equation first — the count of each atom must match on both sides.

2. Convert what you are given into moles (usually grams divided by molar mass).

3. Use the mole ratio from the balanced equation to find moles of what the question asks for.

4. Convert those moles back into the requested unit (e.g., grams) by multiplying by molar mass.

5. Check your units and rounding before locking in an answer.

A focused chemistry review plan

You are juggling four or five sections, so chemistry cannot eat your whole calendar. Give it a focused week — concept first, practice second — and work it by yield instead of grinding front to back. The biggest time-saver: pair the calculation topics with your math review so you are not learning the same skill twice. Build a one-page formula sheet as you go (the mole number, molarity as moles per liter, pH basics, conservation of mass), then lean on study techniques that actually stick — active recall and short, spaced sessions beat one marathon reread every time.

The review sequence

1. Confirm chemistry is on your school’s list. Never skip this one.

2. Learn atomic structure and the periodic table — everything else builds on them.

3. Move to bonding and reaction types, then practice balancing equations.

4. Hit the math block — the mole, stoichiometry, molarity, and pH — studied right next to your math prep.

5. Fill in acids and bases plus solutions.

6. Skim nuclear chemistry last (low-yield), then take a timed practice set and fix whatever is shaky.

Practice: sample HESI A2 chemistry questions

These sample questions mix concept and calculation — exactly what the real section does. Try each before you peek at the answer. For the mole and stoichiometry, Khan Academy’s free unit on the mole and stoichiometry walks you through it at your own pace.

1. An atom has 11 protons. What is its atomic number? (a) 11 (b) 22 (c) 12 (d) 23

Answer: a. Atomic number always equals the number of protons, so 11 protons means atomic number 11 — sodium.

2. Which bond forms when a metal hands an electron to a nonmetal, like in NaCl? (a) covalent (b) ionic (c) hydrogen (d) metallic

Answer: b. Handing off an electron means ionic; covalent bonds share instead. NaCl is the textbook metal-to-nonmetal transfer.

3. Balance this equation: H₂ + O₂ → H₂O. The correct coefficients are: (a) 1, 1, 1 (b) 2, 1, 2 (c) 2, 2, 2 (d) 1, 2, 1

Answer: b. You need 2 H₂ + O₂ → 2 H₂O — four hydrogen and two oxygen on each side. Mass is conserved, so the sides must match.

4. What is the molarity of a solution with 3 moles of solute in 1.5 liters? (a) 1.5 M (b) 2 M (c) 4.5 M (d) 0.5 M

Answer: b. Molarity is moles divided by liters, so 3 ÷ 1.5 = 2 M. The 4.5 trap multiplies instead of dividing.

5. A solution has a pH of 4. It is: (a) basic (b) neutral (c) acidic (d) saturated

Answer: c. Below 7 is acidic, 7 is neutral, above 7 is basic — a pH of 4 is firmly acidic.

6. How many moles are in 36 grams of water (molar mass ≈ 18 g/mol)? (a) 1 mole (b) 2 moles (c) 0.5 mole (d) 18 moles

Answer: b. Grams divided by molar mass gives moles, so 36 ÷ 18 = 2 moles — the most useful conversion in the whole section.

Frequently asked questions

What is on the HESI A2 chemistry section?

Introductory chemistry — about nine topics from atomic structure to acids and bases (the ranked list is above). Confirm the current topics with Elsevier, since schools customize the exam.

Is HESI A2 chemistry hard?

The concept topics are manageable. The calculation ones — mostly the mole, stoichiometry, and molarity — are where people lose points, especially if math has never been their thing. Study those next to your math prep and the section gets friendlier.

Do I need math for HESI A2 chemistry?

Yes, some. A handful of topics use ratios, conversions, and the pH scale. Treat the math-heavy chemistry and the math section as one study block so you are not relearning the same skill twice.

How many chemistry questions are on the HESI A2?

Usually 25 in about 25 minutes when it is required, though some versions add unscored items. Counts and requirements vary by program, so check with your school and Elsevier before you plan.

What score do I need on HESI A2 chemistry?

There is no official passing score — each program sets its own cut score, often 75% or higher. Ask yours for the required composite and any section minimums.

What is the most important chemistry topic to study?

The mole and stoichiometry — high-yield and calculation-based, so they trip up the most people. Nail those, plus atomic structure and acids and bases, before you bother with low-yield nuclear chemistry.

Conclusion

Chemistry is the HESI A2 section you are least likely to need, so confirm your program requires it before you burn a single hour. If it does, see it for what it is: intro chemistry with a small math problem hiding inside. Handle the mole, stoichiometry, molarity, and pH next to your math review, and the rest is recall you can build in about a week. Start with atomic structure, rank your topics by yield, and practice the calculations until the setup feels boring. If you would rather have a plan that spots your weak topics for you, Testavia’s pre-nursing prep maps the whole thing to your timeline.