⚗️ Chemistry: Matter and Reactions

Part 1 of 7 — Chemistry on the ASVAB

Topic Overview

Where Chemistry Fits

General Science (GS) is the first subtest you see on the CAT-ASVAB. It has 15 scored questions and a 12-minute limit, which works out to about 48 seconds per question. GS mixes life science, earth and space science, and physical science, and the official content outline puts atomic structure and chemistry inside the physical-science share.

Two rules about the computer test matter right now:

• You can't go back. Once you answer a question, it is locked in.
• Some questions may be unscored tryout items, and you can't tell which ones, so treat every question as if it counts.

Key Fact: GS chemistry is high-school level. No question asks you to memorize the whole periodic table or do long calculations. It asks for one fact or one short step, and you do any arithmetic on scratch paper (no calculator).

⚗️ Chemistry: Matter and Reactions

Part 2 of 7 — Matter, States and Changes

What Matter Is

Matter is anything that has mass and takes up space (has volume). Air, water, steel and your own body are all matter. Light, heat and sound are not matter: they are forms of energy.

One cubic centimeter and one milliliter are the same volume: $1 \text{ cm}^3 = 1 \text{ mL}$.

Density

$\text{density} = \frac{\text{mass}}{\text{volume}}$

Water's density is about 1 g/cm³ (1 g/mL). That single number answers most floating questions:

Density belongs to the substance, not the size of the piece. Cut a steel bar in half and each half has half the mass and half the volume, so the density stays the same.

Density and particle spacing

Density depends on how tightly the particles are packed. When the same mass is squeezed into less space (particles closer together), density goes up. When particles spread out, density goes down. That is why a gas is far less dense than the same substance as a liquid.

Key Fact: Water is the famous exception. In ice, water molecules lock into an open, spread-out pattern, so ice is less dense than liquid water and floats. That is why lakes freeze from the top down.

⚗️ Chemistry: Matter and Reactions

Part 3 of 7 — Atoms and the Periodic Table

Element, Atom, Molecule

Every compound is made of molecules or ions, but not every molecule is a compound: $O_2$ is a molecule of a single element.

Inside the Atom

Memory hook: P-E-N. Protons are Positive, Electrons carry the nEgative charge, Neutrons are Neutral.

The nucleus holds almost all of the atom's mass but takes up a tiny fraction of its space. Most of an atom is empty space where the electrons move.

The two numbers

So: $\text{neutrons} = \text{mass number} - \text{atomic number}$.

In a neutral atom, electrons = protons, so the charges cancel.

⚗️ Chemistry: Matter and Reactions

Part 4 of 7 — Compounds, Mixtures and Solutions

Sorting All Matter

Every sample of matter is either a pure substance or a mixture:

Compound vs mixture: the four tests

The classic example: sodium is a soft metal that reacts violently with water, and chlorine is a poisonous green gas. Bonded together as sodium chloride, they make table salt, which you sprinkle on food. New substance, new properties: a compound.

Solutions

A solution is a homogeneous mixture.

Water is called the "universal solvent" because it dissolves more substances than any other common liquid. It does not dissolve everything: oil and water stay separate ("like dissolves like").

Temperature and solubility:

• Most solids dissolve better in hot water (sugar in hot tea vs iced tea).
• Gases dissolve better in cold water. A warm soda loses its fizz faster, and warm water holds less dissolved oxygen.

⚗️ Chemistry: Matter and Reactions

Part 5 of 7 — Acids, Bases and Chemical Reactions

The pH Scale

pH measures how acidic or basic (alkaline) a solution is, on a scale from 0 to 14:

Key Fact: Each step on the pH scale is a factor of 10. A pH 3 solution is 10 times as acidic as pH 4 and 100 times as acidic as pH 5. Lower pH = more acidic.

Acids vs bases

Memory hook: "BRA" = Blue turns Red in Acid. (Never taste or touch lab chemicals to test them: indicators exist for a reason.)

Neutralization

An acid and a base react to cancel each other out:

$\text{acid} + \text{base} \rightarrow \text{salt} + \text{water}$

For example, hydrochloric acid plus sodium hydroxide gives table salt and water: $HCl + NaOH \rightarrow NaCl + H_2O$. An antacid tablet (a mild base) neutralizes extra stomach acid, and baking soda is used to neutralize acid spills.

⚗️ Chemistry: Matter and Reactions

Part 6 of 7 — Test Strategy and Common Traps

Your Clock on GS

On the CAT-ASVAB, remaining time and remaining questions show in the lower-right corner of the screen.

How the computer test treats you

• No going back. Answer each question for real before you move on: there is no "flag and return."
• Adaptive. The first question is of average difficulty; a correct answer usually brings a harder question and a wrong one an easier question. A hard question means you are doing well, so don't panic.
• Tryout questions may be mixed in, and you can't tell which, so treat every question as scored.
• Don't speed-guess at the end. Unfinished questions are scored as if you had guessed at random, and the official guidance says the CAT applies a relatively large penalty when several wrong answers come in a row near the end of a subtest. If time is short, keep reading and genuinely answering.
• Paper test: answer every question; there is no penalty for guessing.

Key Fact: Most chemistry questions take one fact. If you know the fact, answer in 15–20 seconds and bank the time for the questions that need a step of reasoning.

⚗️ Chemistry: Matter and Reactions

Part 7 of 7 — Mixed Mastery Set

How to Use This Set

These 11 questions mix everything from Parts 2–5, in the same style and difficulty range as GS chemistry on the ASVAB: a few quick recall questions, several one-step reasoning questions, and a few that need careful thought.

• Give yourself about 48 seconds per question, the CAT-ASVAB pace.
• Do the arithmetic on scratch paper; no calculator.
• When you miss one, go back to the part it came from: