CWS Water Chemistry & Contaminant Identification 3 — Questions and Answers
Question 1: Which type of hardness cannot be removed by boiling water?
- Temporary hardness
- Carbonate hardness
- Permanent hardness (Correct answer)
- Bicarbonate hardness
Correct answer: Permanent hardness
Permanent (non-carbonate) hardness is caused by calcium and magnesium sulfates and chlorides, which are not removed by boiling.
Question 2: Langelier Saturation Index (LSI) is used to predict water's tendency to:
- Grow bacteria
- Form or dissolve calcium carbonate scale (Correct answer)
- Adsorb heavy metals
- React with chlorine disinfectants
Correct answer: Form or dissolve calcium carbonate scale
The LSI predicts whether water will precipitate (positive LSI) or dissolve (negative LSI) calcium carbonate scale.
Question 3: Arsenic contamination in groundwater is most commonly associated with:
- Industrial discharge only
- Natural geological formations (Correct answer)
- Agricultural runoff
- Chlorination byproducts
Correct answer: Natural geological formations
Arsenic occurs naturally in many geological formations and can leach into groundwater, especially in anaerobic conditions.
Question 4: The presence of hydrogen sulfide gas in water is most commonly detected by:
- pH measurement
- Rotten egg odor (Correct answer)
- Turbidity testing
- Hardness titration
Correct answer: Rotten egg odor
Hydrogen sulfide produces a distinctive rotten egg odor detectable at very low concentrations (below 0.5 ppb).
Question 5: Which ion is responsible for 'blue staining' on plumbing fixtures?
- Iron (Fe²⁺)
- Manganese (Mn²⁺)
- Copper (Cu²⁺) (Correct answer)
- Zinc (Zn²⁺)
Correct answer: Copper (Cu²⁺)
Copper ions in water cause characteristic blue-green staining on sinks, tubs, and fixtures due to copper corrosion.
Question 6: What does a nephelometer measure in a water sample?
- Dissolved oxygen concentration
- Light scattering caused by suspended particles (Correct answer)
- Total dissolved solids content
- Oxidation-reduction potential
Correct answer: Light scattering caused by suspended particles
A nephelometer measures turbidity by quantifying the scattering of light by suspended particles, reported in NTU.
Question 7: Radium in drinking water is primarily regulated because it is:
- A neurotoxin at high concentrations
- A radioactive element linked to bone cancer risk (Correct answer)
- A precursor to disinfection byproducts
- A cause of aesthetic odor problems
Correct answer: A radioactive element linked to bone cancer risk
Radium is regulated in drinking water because it is radioactive and accumulates in bones, increasing bone cancer risk.
CWS Water Chemistry & Contaminant Identification 3
Which type of hardness cannot be removed by boiling water?