CWEA LABORATORY ANALYST EXAM ALL GRADES 2025/2026 BANK | ACCURATE REAL
EXAM VERSIONS | CURRENTLY TESTING WITH A STUDY GUIDE
Question 1
Which major anion is commonly found in natural waters and can impart a salty taste at high
concentrations?
A) Sulfate
B) Nitrate
C) Chloride
D) Carbonate
E) Orthophosphate
Correct Answer: C) Chloride
Rationale: Chloride is a major anion found in many natural waters. While essential in
certain concentrations, high levels can significantly alter the taste of water, making it taste
salty.
Question 2
What are the two primary sources that increase chloride concentration in domestic wastewater?
A) Agricultural runoff and industrial cooling
B) Human diet and water softeners
C) Atmospheric deposition and volcanic activity
D) Decomposition of algae and aquatic plants
E) Leaching from PVC pipes
Correct Answer: B) Human diet and water softeners
Rationale: Chloride is excreted in the human diet and is also a byproduct of the ion
exchange process in water softeners, both of which are flushed into the sanitary sewer
system.
Question 3
What are the two most prevalent methods used in the laboratory to measure chloride?
A) Gravimetric and Spectrophotometric
B) Ion Chromatography and Distillation
C) Argentometric and Mercuric Nitrate
D) Potentiometric and Nephelometric
E) Colorimetric and Titrimetric (EDTA)
Correct Answer: C) Argentometric and Mercuric Nitrate
Rationale: The Argentometric (Silver Nitrate) method and the Mercuric Nitrate method are
the standard titrimetric procedures for determining chloride concentration.
Question 4
In the Argentometric method for chloride, what is the standard titrant used?
A) Mercuric Nitrate (Hg(NO3)2)
B) Silver Nitrate (AgNO3)
C) Potassium Chromate (K2CrO4)
, 2
D) Sulfuric Acid (H2SO4)
E) Phenylarsine Oxide (PAO)
Correct Answer: B) Silver Nitrate (AgNO3)
Rationale: The Argentometric method relies on the titration of the sample with a standard
solution of silver nitrate.
Question 5
What indicator is used in the Argentometric chloride titration, and what is the color at the end
point?
A) Phenolphthalein; pink
B) Diphenyl carbazone; purple
C) Chromate ions; reddish-brown silver chromate
D) Eriochrome Black T; blue
E) Methyl orange; yellow
Correct Answer: C) Chromate ions; reddish-brown silver chromate
Rationale: Chromate ions react with excess silver ions after all chloride has been
precipitated, forming reddish silver chromate at the end point.
Question 6
When performing the Mercuric Nitrate method for chloride, the pH of the sample must be
adjusted to what range?
A) 1.0 to 2.0
B) 2.3 to 2.8
C) 4.5 to 5.5
D) 7.0 to 8.0
E) 10.0 to 11.0
Correct Answer: B) 2.3 to 2.8
Rationale: The reaction between mercuric ions and chloride requires an acidic environment,
specifically between pH 2.3 and 2.8, to ensure the indicator functions correctly.
Question 7
What is the end point color change observed in the Mercuric Nitrate method using diphenyl
carbazone?
A) Yellow to green
B) Colorless to pink
C) Blue to purple
D) Clear to cloudy white
E) Red to yellow
Correct Answer: C) Change from blue to purple in presence of mercury
Rationale: In the presence of excess mercuric ions (after chloride is complexed), the
diphenyl carbazone indicator changes from blue to purple.
, 3
Question 8
Which of the following ions is NOT listed as a common interference for the Mercuric Nitrate
method?
A) Sulfide
B) Bromide
C) Iodide
D) Calcium
E) Orthophosphate (over 30 ppm)
Correct Answer: D) Calcium
Rationale: Sulfide, bromide, iodide, and high concentrations of orthophosphate interfere
with the mercury-chloride reaction. Calcium is a common cation that does not interfere
with this specific titration.
Question 9
Why is the Mercuric Nitrate titration method currently falling into disuse in many laboratories?
A) It is not accurate enough
B) The titrant is too expensive
C) Mercury creates a hazardous waste problem
D) The end point is too difficult to see
E) It requires a 5-day incubation
Correct Answer: C) Mercury creates a hazardous waste problem
Rationale: Due to the toxicity of mercury and the strict regulations regarding hazardous
waste disposal, many labs are switching to the Argentometric or Ion Chromatography
methods.
Question 10
Color in water can be caused by metal ions, industrial pollution, or:
A) Excessive dissolved oxygen
B) Decaying vegetable matter
C) High conductivity
D) Use of plastic containers
E) Pure distilled water
Correct Answer: B) Decaying vegetable matter
Rationale: Natural color in water often results from the presence of tannins and lignins
derived from decaying vegetation.
Question 11
How is color typically measured in the laboratory according to the visual comparison method?
A) Using a spectrophotometer at 600 nm
B) Comparing the sample to standards in matched Nessler tubes
C) Filtering the sample through a 0.45 micron filter only
, 4
D) Titrating with silver nitrate
E) Using a pH meter
Correct Answer: B) Comparing the sample to standards in matched Nessler tubes
Rationale: The standard method involves a visual comparison of the sample against a series
of color standards in specific glass tubes called Nessler tubes.
Question 12
The standards used for color measurement are prepared using a solution containing:
A) Sodium Chloride and Silver Nitrate
B) Platinum (as chloroplatinate) and Cobaltous Chloride
C) Sulfuric acid and Potassium Dichromate
D) Calcium Carbonate and Magnesium Sulfate
E) Glucose and Glutamic Acid
Correct Answer: B) Platinum (as chloroplatinate) and Cobaltous Chloride
Rationale: The Platinum-Cobalt scale is the standard for water color measurement, where
color is measured in "Platinum-Cobalt Units."
Question 13
One standard unit of color is defined as the color resulting from:
A) 1 mg of gold/L
B) 1 mg of platinum/L
C) 1 mg of iron/L
D) 1 mg of cobalt/L
E) 1 mg of chloride/L
Correct Answer: B) One unit = color resulting from 1 mg of platinum/L
Rationale: The definition of a color unit is based on the concentration of platinum in the
standard solution.
Question 14
What is the difference between "True Color" and "Apparent Color"?
A) True color is measured with a meter; Apparent is visual
B) True color includes turbidity; Apparent does not
C) True color is measured after removing turbidity; Apparent includes suspended solids
D) True color is measured at 20°C; Apparent at 25°C
E) There is no difference
Correct Answer: C) True color is measured after removing turbidity; Apparent includes
suspended solids
Rationale: True color refers only to dissolved substances. Apparent color includes the effects
of suspended matter (turbidity).
EXAM VERSIONS | CURRENTLY TESTING WITH A STUDY GUIDE
Question 1
Which major anion is commonly found in natural waters and can impart a salty taste at high
concentrations?
A) Sulfate
B) Nitrate
C) Chloride
D) Carbonate
E) Orthophosphate
Correct Answer: C) Chloride
Rationale: Chloride is a major anion found in many natural waters. While essential in
certain concentrations, high levels can significantly alter the taste of water, making it taste
salty.
Question 2
What are the two primary sources that increase chloride concentration in domestic wastewater?
A) Agricultural runoff and industrial cooling
B) Human diet and water softeners
C) Atmospheric deposition and volcanic activity
D) Decomposition of algae and aquatic plants
E) Leaching from PVC pipes
Correct Answer: B) Human diet and water softeners
Rationale: Chloride is excreted in the human diet and is also a byproduct of the ion
exchange process in water softeners, both of which are flushed into the sanitary sewer
system.
Question 3
What are the two most prevalent methods used in the laboratory to measure chloride?
A) Gravimetric and Spectrophotometric
B) Ion Chromatography and Distillation
C) Argentometric and Mercuric Nitrate
D) Potentiometric and Nephelometric
E) Colorimetric and Titrimetric (EDTA)
Correct Answer: C) Argentometric and Mercuric Nitrate
Rationale: The Argentometric (Silver Nitrate) method and the Mercuric Nitrate method are
the standard titrimetric procedures for determining chloride concentration.
Question 4
In the Argentometric method for chloride, what is the standard titrant used?
A) Mercuric Nitrate (Hg(NO3)2)
B) Silver Nitrate (AgNO3)
C) Potassium Chromate (K2CrO4)
, 2
D) Sulfuric Acid (H2SO4)
E) Phenylarsine Oxide (PAO)
Correct Answer: B) Silver Nitrate (AgNO3)
Rationale: The Argentometric method relies on the titration of the sample with a standard
solution of silver nitrate.
Question 5
What indicator is used in the Argentometric chloride titration, and what is the color at the end
point?
A) Phenolphthalein; pink
B) Diphenyl carbazone; purple
C) Chromate ions; reddish-brown silver chromate
D) Eriochrome Black T; blue
E) Methyl orange; yellow
Correct Answer: C) Chromate ions; reddish-brown silver chromate
Rationale: Chromate ions react with excess silver ions after all chloride has been
precipitated, forming reddish silver chromate at the end point.
Question 6
When performing the Mercuric Nitrate method for chloride, the pH of the sample must be
adjusted to what range?
A) 1.0 to 2.0
B) 2.3 to 2.8
C) 4.5 to 5.5
D) 7.0 to 8.0
E) 10.0 to 11.0
Correct Answer: B) 2.3 to 2.8
Rationale: The reaction between mercuric ions and chloride requires an acidic environment,
specifically between pH 2.3 and 2.8, to ensure the indicator functions correctly.
Question 7
What is the end point color change observed in the Mercuric Nitrate method using diphenyl
carbazone?
A) Yellow to green
B) Colorless to pink
C) Blue to purple
D) Clear to cloudy white
E) Red to yellow
Correct Answer: C) Change from blue to purple in presence of mercury
Rationale: In the presence of excess mercuric ions (after chloride is complexed), the
diphenyl carbazone indicator changes from blue to purple.
, 3
Question 8
Which of the following ions is NOT listed as a common interference for the Mercuric Nitrate
method?
A) Sulfide
B) Bromide
C) Iodide
D) Calcium
E) Orthophosphate (over 30 ppm)
Correct Answer: D) Calcium
Rationale: Sulfide, bromide, iodide, and high concentrations of orthophosphate interfere
with the mercury-chloride reaction. Calcium is a common cation that does not interfere
with this specific titration.
Question 9
Why is the Mercuric Nitrate titration method currently falling into disuse in many laboratories?
A) It is not accurate enough
B) The titrant is too expensive
C) Mercury creates a hazardous waste problem
D) The end point is too difficult to see
E) It requires a 5-day incubation
Correct Answer: C) Mercury creates a hazardous waste problem
Rationale: Due to the toxicity of mercury and the strict regulations regarding hazardous
waste disposal, many labs are switching to the Argentometric or Ion Chromatography
methods.
Question 10
Color in water can be caused by metal ions, industrial pollution, or:
A) Excessive dissolved oxygen
B) Decaying vegetable matter
C) High conductivity
D) Use of plastic containers
E) Pure distilled water
Correct Answer: B) Decaying vegetable matter
Rationale: Natural color in water often results from the presence of tannins and lignins
derived from decaying vegetation.
Question 11
How is color typically measured in the laboratory according to the visual comparison method?
A) Using a spectrophotometer at 600 nm
B) Comparing the sample to standards in matched Nessler tubes
C) Filtering the sample through a 0.45 micron filter only
, 4
D) Titrating with silver nitrate
E) Using a pH meter
Correct Answer: B) Comparing the sample to standards in matched Nessler tubes
Rationale: The standard method involves a visual comparison of the sample against a series
of color standards in specific glass tubes called Nessler tubes.
Question 12
The standards used for color measurement are prepared using a solution containing:
A) Sodium Chloride and Silver Nitrate
B) Platinum (as chloroplatinate) and Cobaltous Chloride
C) Sulfuric acid and Potassium Dichromate
D) Calcium Carbonate and Magnesium Sulfate
E) Glucose and Glutamic Acid
Correct Answer: B) Platinum (as chloroplatinate) and Cobaltous Chloride
Rationale: The Platinum-Cobalt scale is the standard for water color measurement, where
color is measured in "Platinum-Cobalt Units."
Question 13
One standard unit of color is defined as the color resulting from:
A) 1 mg of gold/L
B) 1 mg of platinum/L
C) 1 mg of iron/L
D) 1 mg of cobalt/L
E) 1 mg of chloride/L
Correct Answer: B) One unit = color resulting from 1 mg of platinum/L
Rationale: The definition of a color unit is based on the concentration of platinum in the
standard solution.
Question 14
What is the difference between "True Color" and "Apparent Color"?
A) True color is measured with a meter; Apparent is visual
B) True color includes turbidity; Apparent does not
C) True color is measured after removing turbidity; Apparent includes suspended solids
D) True color is measured at 20°C; Apparent at 25°C
E) There is no difference
Correct Answer: C) True color is measured after removing turbidity; Apparent includes
suspended solids
Rationale: True color refers only to dissolved substances. Apparent color includes the effects
of suspended matter (turbidity).
