Chemistry Knowledge You Need for the ACT Science Section

April 19, 2016

You may be surprised to find out that you don't need outside science knowledge to answer most of the questions on the ACT science section, but it generally helps on 5-6 questions, and 1 or 2 generally will require it.  Coming equipped with a fundamental knowledge of the basics of biology, chemistry, physics, and the earth sciences will generally cover you on those “outside knowledge” questions, while rare, could mean the difference between a 32 and a 36.  But don’t just take it from us. 

This is from the ACT: “Advanced knowledge in these subjects is not required, but background knowledge acquired in general, introductory science courses is needed to answer some of the questions. The test emphasizes scientific reasoning skills over recall of scientific content, skill in mathematics, or reading ability.”

Act Science

In today’s blog we will focus on the key topics/core vocabulary for chemistry passages:

  • Phase Changes
  • Charged Particles
  • Molar Mass
  • Freezing/Boiling Point of Water
  • Basic Molecule Structure
  • pH Scale


Topic #1: Phase Changes

Phase changes are transition points between the three states of matter: solid, liquid, and gas. For water, that's changing from ice to water to steam. The photo below depicts a sculpture by Andy Goldsworthy, who takes advantage of phase changes in his work. He builds ice sculptures that melt away when the air surrounding them warms up.

ACT Science

  • The transition point between solid and liquid can be referred to as the freezing point or as the melting point. This is because when a material goes from liquid to solid, we call it freezing, while we call a transition in the other direction melting; however both processes occur at the same temperature.
  • Below its freezing/melting point, a material will be in solid form. That's why water is ice below 0C (32F).
  • Above its freezing/melting point, a material will be in liquid form.
  • The transition point between liquid and gas can be referred to as the boiling point or the condensation point. Matter transitioning from gas to liquid is called condensation, while matter transitioning from liquid to gas is called boiling.
  • Above its boiling/condensation point, a material will be a gas.


Topic #2: Charged Particles

Atoms are composed of three types of particles: protons, electrons, and neutrons. Protons are positively charged, electrons are negatively charged, and neutrons are neutral: they have no charge.

Like charges repel each other, while opposite charges attract each other. For example, two positive charges will repel each other, while a positive and a negative charge will attract.

When charged particles from the sun hit our atmosphere, the results are beautiful. This happens most frequently at the poles to give us the Northern Lights (captured below).

Northern Lights

Topic #3: Molar Mass

Remember the periodic table? The masses listed for each element on the table are given as molar masses: a number which tells you the mass in grams of one mole of the substance. The molar mass of a molecule is the sum of the molar masses of the atoms it is composed of.

Topic #4: Freezing/Boiling Point of Water in Celsius

Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.  Memorize those numbers!

Topic #5: Basic Molecule Structure

The ACT Science section expects you to know the basic molecular structure of Sugar, Fat, Protein and Nucleic Acids.

C6H12O6 is the basic sugar molecule structure

Know that fats are made up of C (Carbon), H (Hydrogen), and O (Oxygen). To differentiate fats from sugar: fats have nearly twice the number of H as C and a very small number of O. Fats are much bigger in size than sugar. For example, an unsaturated fat triglyceride has a chemical formula of C55H98O6.

Amino acids:
Proteins are composed of amino acids. All proteins contain C, H, O and N (Nitrogen).

Nucleic acids:
Two types of nucleic acids that we already discussed are DNA and RNA.  Nucleic acids are made up of 3 parts: a 5-carbon sugar, a phosphate group, and a nitrogenous base. Nucleic acids are different from Sugar, Fat, and Proteins because they are made up of P (Phosphorus) and N in addition to C, H, and O.

Topic #6: pH Scale
A pH scale is a measure of how acidic or basic a substance is.  All you need to know is that a pH of below 7 is acidic, above 7 is basic, and at 7 is considered neutral.

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