Lesson · C.4.1
Acids and bases
How acids and bases behave in water, what the pH scale actually measures, and the reference ranges the HESI A2 expects you to recognise on sight.
ObjectiveC.4.1Read5 minExam weightAqueous and Nuclear Chemistry ≈ 16% of Chemistry
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See editions and pricing →What you will be able to do
- Define an acid and a base using the proton donor and proton acceptor model
- Read the pH scale correctly, including which direction is more acidic
- Recall the normal pH ranges for blood and other common body fluids
What the lesson concludes
- An acid donates a proton (H⁺); a base accepts one, most often via a hydroxide (OH⁻) group.
- The pH scale runs 0 to 14. Lower means more acidic, higher means more basic, and 7 is neutral.
- Water is amphoteric: it can act as an acid or a base, which is why pure water still shows a small, equal concentration of both ions.
- Arterial blood sits in a narrow band of 7.35 to 7.45. A shift outside that range is treated as acidosis or alkalosis, not just a lab number.
- Mixing an acid with a base moves both solutions toward neutral, a reaction the HESI tests as often as the definitions themselves.