CWS Water Chemistry & Contaminant Identification 2 — Questions and Answers
Question 1: Which parameter is used to measure the ability of water to neutralize acids?
- Hardness
- Alkalinity (Correct answer)
- pH
- Turbidity
Correct answer: Alkalinity
Alkalinity measures water's capacity to neutralize acids, primarily due to bicarbonate, carbonate, and hydroxide ions.
Question 2: What is the maximum contaminant level (MCL) for nitrates in drinking water set by the EPA?
- 5 mg/L
- 10 mg/L (Correct answer)
- 15 mg/L
- 20 mg/L
Correct answer: 10 mg/L
The EPA MCL for nitrates in drinking water is 10 mg/L (as nitrogen) to prevent methemoglobinemia in infants.
Question 3: Trihalomethanes (THMs) in drinking water are primarily formed when:
- Iron reacts with dissolved oxygen
- Chlorine reacts with natural organic matter (Correct answer)
- Manganese oxidizes in high pH water
- Hardness minerals precipitate during heating
Correct answer: Chlorine reacts with natural organic matter
THMs form as disinfection byproducts when chlorine reacts with naturally occurring organic matter in source water.
Question 4: A water sample has a pH of 5.5. This water would be classified as:
- Slightly alkaline
- Neutral
- Slightly acidic (Correct answer)
- Highly alkaline
Correct answer: Slightly acidic
A pH of 5.5 is below the neutral point of 7.0, making the water slightly acidic.
Question 5: Which dissolved gas is the primary cause of red water complaints related to iron?
- Carbon dioxide
- Hydrogen sulfide
- Oxygen (Correct answer)
- Chlorine
Correct answer: Oxygen
Dissolved oxygen causes ferrous (clear) iron to oxidize into ferric (red/brown) iron, producing red water complaints.
Question 6: Total Dissolved Solids (TDS) in water is best measured by which method?
- Colorimetric analysis
- Gravimetric analysis after evaporation (Correct answer)
- Titration with EDTA
- Nephelometric turbidity measurement
Correct answer: Gravimetric analysis after evaporation
TDS is measured gravimetrically by filtering a sample, evaporating the water, and weighing the remaining residue.
Question 7: Sodium fluoride is added to drinking water primarily to:
- Reduce corrosion in distribution pipes
- Prevent dental cavities (Correct answer)
- Precipitate hardness minerals
- Remove iron and manganese
Correct answer: Prevent dental cavities
Fluoride is added to drinking water at controlled levels (typically 0.7 mg/L) to prevent tooth decay in the population.
CWS Water Chemistry & Contaminant Identification 2
Which parameter is used to measure the ability of water to neutralize acids?