Problem 4.8: During an acid cleaning your solution sits at

From Chapter 4 Problem Set. Level 3: System Integration.

Question

During an acid cleaning, your solution sits at pH 2.5. You add caustic and the pH moves to 3.5. By what factor did the hydrogen concentration decrease? Explain why a technician might mistakenly think this change was trivial.

Answer

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pH 2.5 → 3.5 = 1 pH unit = 10× decrease in [H⁺]. The technician sees “one point” and thinks the change is small because the pH scale is logarithmic. In reality, about 90% of the hydrogen has already been consumed. The next dose walks into an empty room.