What is a concentrated acid?

• A. An acid that contains a large number of H+ ions.
• B. An acid with low pH
• C. An acid with high pH
• D. An acid that is highly viscous

Answer: (A)

The key idea is how much acid is present in a given volume. In an acid, acidity comes from hydrogen ions (H+). A concentrated acid is one that has a large number of acid particles, so there are many H+ ions per liter of solution. That high number of H+ ions is what makes the solution strongly acidic. The pH value is related to this, since lower pH means higher H+ concentration, but it’s a measure, not the definition. A low pH simply indicates high H+; a high pH would mean basic, not acidic. Viscosity doesn’t relate to how much acid is dissolved, so it isn’t a definition of concentration.