Chemistry Chapter 2: Acids, Bases, and pH

Chapter 2: Atoms, Ions, and Molecules - Acids, Bases, and pH

• Learning Objectives: Define pH, differentiate acidity and basicity, compare and contrast acids and bases, and describe how buffers maintain blood pH in the carbonic acid-bicarbonate buffer system.

pH

• pH is a measure of the relative amount of H+ in a solution.
• The pH scale ranges from 0 to 14.
• pH and H+ concentration are inversely related. As H+ concentration increases, pH decreases. Conversely, as H+ concentration decreases, pH increases.
• A pH of 7 is neutral. pH values below 7 are acidic, and above 7 are basic.
• Each step on the pH scale represents a tenfold difference in H+ concentration.

pH and Solutions

• Neutral solutions have equal concentrations of H+ and OH-.
• Acidic solutions have a greater concentration of H+ than OH-.
• Basic solutions have a greater concentration of OH- than H+.

Acids

• Acids are proton donors, increasing the concentration of free H+.
• Stronger acids have a greater dissociation of H+ than weaker acids.
• Examples include hydrochloric acid (stomach acid) and carbonic acid (in the blood).

Bases

• Bases are proton acceptors, decreasing the concentration of free H+.
• Stronger bases absorb more H+ than weaker bases.
• Examples include ammonia and bleach. Bicarbonate is a weak base that buffers blood pH.

Neutralization

• Neutralization occurs when an acidic or basic solution is returned to a neutral pH (7)
• Acids are neutralized by adding a base.
• Bases are neutralized by adding acid. Example: Medications to neutralize stomach acid often contain a base.

Buffers

• Buffers help prevent major pH changes.
• The carbonic acid-bicarbonate buffer system is critical in maintaining blood pH within a narrow range.
• Carbonic acid (weak acid) and bicarbonate (weak base) act together to resist changes in pH.
• Blood pH is maintained at a critical range of 7.35-7.45.
• Low blood pH is acidosis, while high blood pH is alkalosis.
• Lungs regulate CO2, while kidneys regulate bicarbonate levels for proper pH balance.