Acids and bases on the TEAS 7: pH, neutralization and buffers explained

Where acids and bases sit on TEAS 7

ATI's TEAS 7 content outline lists objective S.3.6, "Describe concepts of acids and bases," as the last of six chemistry objectives, next to S.3.5 on properties of solutions. Chemistry has 8 scored questions in total, so plan on this topic being about one question, possibly two.

This is introductory chemistry: the pH scale, definitions and neutralization. It is not the arterial blood gas interpretation you will learn later in nursing school, although the buffer section below shows where the two meet.

The pH scale and the tenfold rule

OpenStax defines pH as the negative logarithm of the hydronium ion concentration. At 25 C a neutral solution has pH 7, an acidic one is below 7 and a basic one is above 7, and pH plus pOH equals 14. Pure water sits at 7 and milk of magnesia at about 10.5.

Because the scale is logarithmic, each whole pH unit is a tenfold change in hydronium concentration. Worked example: a solution at pH 3 has 10 times the hydronium of one at pH 4 and 10 x 10 x 10 = 1,000 times that of one at pH 6. A common wrong answer treats pH 3 as twice as acidic as pH 6.

What makes a substance an acid or a base

In water, an acid yields hydronium ions (H3O+) by transferring hydrogen ions, and a base yields hydroxide ions (OH-). If a question describes a substance donating a hydrogen ion, it is describing an acid; if it describes accepting one or releasing hydroxide, it is a base.

Strength is about how completely the acid ionizes. OpenStax lists hydrochloric acid and sulfuric acid as strong acids that react completely in water, while acetic acid, the acid in vinegar, is weak and only partly ionizes. Strong does not mean the solution is concentrated; it describes how much of the acid breaks apart.

Neutralization reactions

When an acid and a base react, they form a salt and water. The textbook example is hydrochloric acid plus sodium hydroxide giving sodium chloride plus water: HCl + NaOH gives NaCl + H2O. The equation is already balanced, with one of each atom on both sides.

OpenStax uses antacids as the everyday case: they neutralize excess hydrochloric acid in the stomach. On a question that asks what forms when an acid meets a base, look for salt and water among the choices, and be wary of options that list a gas or a new acid.

Buffers and why blood pH barely moves

A buffer, in OpenStax's words, is a chemical system that prevents a radical change in fluid pH by dampening changes in hydrogen ion concentration. The body's main one is the bicarbonate and carbonic acid pair: bicarbonate takes up excess acid, and carbonic acid takes up excess base.

Normal arterial blood pH stays between 7.35 and 7.45, slightly basic. Below 7.35 is called acidosis and above 7.45 alkalosis. The lungs adjust carbonic acid by exhaling carbon dioxide within minutes, while the kidneys adjust bicarbonate and hydrogen ion excretion over hours to days.

Sources

ATI TEAS Version 7 Content Outline (PDF). Chemistry objectives S.3.5 and S.3.6 wording; 8 scored chemistry questions (checked November 2026).

OpenStax Chemistry 2e, 14.2 pH and pOH. pH = -log[H3O+]; neutral 7, acidic below, basic above at 25 C; pH + pOH = 14; water 7 and milk of magnesia about 10.5; tenfold change per unit.

OpenStax Chemistry 2e, 4.2 Classifying Chemical Reactions. Acids yield hydronium and bases hydroxide; strong acids HCl and sulfuric vs weak acetic acid; neutralization gives salt and water; antacids neutralize stomach HCl.

OpenStax Anatomy and Physiology 2e, 26.4 Acid-Base Balance. Buffer definition; bicarbonate and carbonic acid buffer reactions; lungs regulate CO2 quickly, kidneys regulate bicarbonate over hours to days.

OpenStax Anatomy and Physiology 2e, 26.5 Disorders of Acid-Base Balance. Normal arterial blood pH 7.35 to 7.45; acidosis below 7.35; alkalosis above 7.45.