Water, Acids and Bases

Principles Module 6

Principles Module 7


  • Describe the physical and chemical properties of water and their cause
  • Discuss some of the implications of water’s properties on life processes
  • Explain the concept of pH and buffering

Key points


  • water molecules are bent, which causes them to be polar
    • bond angle due to tetrahedral arrangement of electrons
    • polarity refers to tendency of electrons to be more near O than H
    • polarity results in H-bonding, physical properties of water
    • watch an animated model of water at freezing and boiling temperature (via Chamot Labs
  • the properties of water enable transport through the xylem of plants
  • water is a good solvent: it dissolves solutes; this is due to polarity
  • water moderates temperature because of its high specific heat

Acids & Bases

  • an acid is something that increases H+ concentration in solution
  • a base is something that decreases H+ concentration in solution

In-class activities


You are working the ER one evening when a 4 year-old boy arrives by ambulance with his parents. He is unresponsive, with rapid, deep breathing. His mother is holding a bottle of aspirin that she found open on the floor near him. You immediately order a battery of rapid blood tests on the boy to confirm your suspicion that he has ingested the aspirin. Meanwhile, you intubate the boy and hyperventilate him. A nurse begins to administer activated charcoal to absorb any aspirin in his stomach that has not yet been dissolved.

When the results of the blood tests come in, they confirm your suspicion. The boy’s blood pH is 6.8 (7.4 is normal) and the level of salicylate in the plasma is very high. You order an emergency treatment with intravenous bicarbonate (HCO3) and other treatments to stabilize the patient. Shortly after starting the intravenous bicarbonate treatment, the patient’s breathing returns to a normal rate and he shows signs of stabilizing. Another blood pH test shows his pH returning to the normal range.

Questions for groups

  • If normal blood pH is 7.4, by what factor does the H+ concentration of the patient’s blood differ from the norm? Remember, pH is logarithmic scale.
  • Why was the patient observed to be breathing rapidly and deeply in the emergency room, despite being nearly comatose? Why did you hyperventilate him?
  • Why was the patient’s deep, rapid breathing not helping him much?
  • Why did you order order intravenous bicarbonate? Draw a simple diagram explaining the mechanism of this treatment for systemic acidosis (remember the in-class demonstration).

Adapted from The Case of the Mortified Mom: Acids, pH and Buffers byTerry Platt, Department of Biology, University of Rochester