✓ TradeExamPro

TradeExamPro › Inspector › Pool operator (CPO)

Chemistry practice questions

31 questions from the pool operator (cpo) practice test.

Chemistry practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Free chlorine holds steady at 2.0 ppm while the pH drifts from 7.2 up to 8.0. What happens to disinfection?

  1. It weakens, because less of the chlorine is HOCl
  2. It improves, because more of the chlorine is HOCl
  3. It is unchanged, because free chlorine is the same
  4. It stops, because chlorine cannot exist above 7.8
Show the answer

A. It weakens, because less of the chlorine is HOCl

As pH rises, hypochlorous acid converts to the much weaker hypochlorite ion, so the same free chlorine reading kills more slowly. The reading alone does not tell you how much is in the active form.

Reference: PHTA Pool & Spa Operator Handbook, disinfection chapter

At a pH of about 7.5 and normal pool temperature, roughly what share of the free chlorine is in the active HOCl form?

  1. About 50%
  2. About 97%
  3. About 10%
  4. About 80%
Show the answer

A. About 50%

Hypochlorous acid and hypochlorite ion are about evenly split near pH 7.5. A share near 97% only occurs around pH 6, which is far too corrosive to operate at.

Reference: PHTA Pool & Spa Operator Handbook, disinfection chapter

Chloramines form in pool water when free chlorine reacts with which contaminants?

  1. Calcium and magnesium minerals from very hard fill water
  2. Ammonia and nitrogen compounds from sweat and urine
  3. Carbon dioxide absorbed from the air
  4. Copper and iron from corroding equipment
Show the answer

B. Ammonia and nitrogen compounds from sweat and urine

Chloramines are the product of chlorine combining with nitrogen-containing waste from bathers. Minerals and metals cause scale and stains, not combined chlorine.

Reference: PHTA Pool & Spa Operator Handbook, disinfection chapter

Other topics