CWEA Grade 1 Lab Analyst Practice Test
Questions with 100% Verified Answers
Question 1
HPC media water bath
Correct Answer
45`C, 3hr
Question 2
top loading balance
Correct Answer
used to determine mass; not as precise as an analytical balance
Question 3
Sample labels should include
Correct Answer
unique sample number, sample type, name of collector, date and time of collection,
place of collection, and sample preservative
Question 4
Precision
Correct Answer
a measure of how close a series of measurements are to one another
Question 5
BOD hold time
Correct Answer
48 hours
Page 1 of 165
,Question 6
spectrometer
Correct Answer
a device that spreads light into its different colors
Question 1: Which of the following parameters is most critical to monitor
immediately when a wastewater sample is collected for dissolved oxygen analysis
to prevent biological activity alteration?
A. Chemical Oxygen Demand
B. Biochemical Oxygen Demand
C. Temperature
D. Dissolved Oxygen Fixation
CORRECT ANSWER: D. Dissolved Oxygen Fixation
Rationale: Dissolved oxygen fixation (using manganous sulfate and alkaline iodide-
azide reagents) must be performed immediately in the field at the time of sample
collection to freeze biological activity and fix the dissolved oxygen in a stable form
before titration.
Question 2: What is the primary purpose of adding sulfuric acid to a sample
collected for chemical oxygen demand (COD) analysis?
A. To neutralize basic compounds and prevent foaming
B. To preserve the sample by lowering the pH to less than 2 and halting biological
activity
C. To oxidize organic compounds prior to digestion
D. To precipitate interfering metal ions out of solution
CORRECT ANSWER: B. To preserve the sample by lowering the pH to less than 2
and halting biological activity
Rationale: Acidifying the COD sample with sulfuric acid to a pH of less than or equal
to 2 inhibits microbial degradation of the organic matter, ensuring the sample
remains representative until laboratory analysis can be performed.
Question 3: In a standard spectrophotometric determination, what law states that
absorbance is directly proportional to the concentration of the absorbing species in
the solution?
A. Henry's Law
B. Boyle's Law
Page 2 of 165
,C. Beer-Lambert Law
D. Dalton's Law
CORRECT ANSWER: C. Beer-Lambert Law
Rationale: The Beer-Lambert Law establishes the linear relationship between
absorbance and concentration, which is the foundational principle underlying most
colorimetric and spectrophotometric wastewater analyses.
Question 4: When performing a total suspended solids (TSS) analysis, what is the
standard drying temperature range for the glass-fiber filter and residue?
A. 103 to 105 degrees Celsius
B. 179 to 181 degrees Celsius
C. 540 to 560 degrees Celsius
D. 99 to 100 degrees Celsius
CORRECT ANSWER: A. 103 to 105 degrees Celsius
Rationale: Drying the filter at 103 to 105 degrees Celsius evaporates all
uncombined moisture without volatilizing or decomposing the organic fraction of the
suspended solids.
Question 5: Which piece of glassware is calibrated to contain a precise volume at a
specific temperature and is used for preparing standard solutions?
A. Erlenmeyer flask
B. Volumetric flask
C. Graduated cylinder
D. Beaker
CORRECT ANSWER: B. Volumetric flask
Rationale: Volumetric flasks are Class A glassware specifically designed to contain
an exact, certified volume of liquid when filled to the calibration mark, making them
essential for accurate standard solution preparation.
Question 6: What safety equipment should always be used when handling
concentrated acids and strong bases in a laboratory setting?
A. Chemical splash goggles, face shield, and chemical-resistant gloves
B. Standard prescription eyeglasses and cotton lab coat
C. Heat-resistant leather gloves and ear protection
D. Dust mask and latex examination gloves
Page 3 of 165
, CORRECT ANSWER: A. Chemical splash goggles, face shield, and chemical-
resistant gloves
Rationale: Concentrated acids and bases pose severe splash and corrosion
hazards, requiring comprehensive eye, face, and hand protection such as splash
goggles, a full-face shield, and heavy-duty chemical-resistant gloves.
Question 7: In the Winkler titration method for dissolved oxygen, what titrant is
commonly used to titrate the liberated iodine?
A. Silver nitrate
B. Sodium thiosulfate
C. Hydrochloric acid
D. Sodium hydroxide
CORRECT ANSWER: B. Sodium thiosulfate
Rationale: Sodium thiosulfate is the standard titrant used in the iodometric Winkler
method, reacting stoichiometrically with the free iodine released during the multi-
step chemical fixation process.
Question 8: What is the primary hazard associated with the digestion step of the
Chemical Oxygen Demand (COD) test using potassium dichromate and
concentrated sulfuric acid?
A. Production of explosive hydrogen gas
B. Extreme exothermic reaction and high pressure buildup in sealed vessels
C. Rapid volatilization of toxic carbon monoxide gas
D. Immediate precipitation of toxic lead compounds
CORRECT ANSWER: B. Extreme exothermic reaction and high pressure buildup in
sealed vessels
Rationale: Mixing concentrated sulfuric acid with water and organic samples
generates intense heat, and closed-vessel digestion creates significant pressure,
requiring proper containment, shielding, and safety glasses.
Question 9: Which microbial indicator group is traditionally used in wastewater
laboratories to assess the bacteriological safety and sanitary quality of treated
effluents?
A. Coliform group
B. Nitrifying bacteria
C. Sulfate-reducing bacteria
Page 4 of 165
Questions with 100% Verified Answers
Question 1
HPC media water bath
Correct Answer
45`C, 3hr
Question 2
top loading balance
Correct Answer
used to determine mass; not as precise as an analytical balance
Question 3
Sample labels should include
Correct Answer
unique sample number, sample type, name of collector, date and time of collection,
place of collection, and sample preservative
Question 4
Precision
Correct Answer
a measure of how close a series of measurements are to one another
Question 5
BOD hold time
Correct Answer
48 hours
Page 1 of 165
,Question 6
spectrometer
Correct Answer
a device that spreads light into its different colors
Question 1: Which of the following parameters is most critical to monitor
immediately when a wastewater sample is collected for dissolved oxygen analysis
to prevent biological activity alteration?
A. Chemical Oxygen Demand
B. Biochemical Oxygen Demand
C. Temperature
D. Dissolved Oxygen Fixation
CORRECT ANSWER: D. Dissolved Oxygen Fixation
Rationale: Dissolved oxygen fixation (using manganous sulfate and alkaline iodide-
azide reagents) must be performed immediately in the field at the time of sample
collection to freeze biological activity and fix the dissolved oxygen in a stable form
before titration.
Question 2: What is the primary purpose of adding sulfuric acid to a sample
collected for chemical oxygen demand (COD) analysis?
A. To neutralize basic compounds and prevent foaming
B. To preserve the sample by lowering the pH to less than 2 and halting biological
activity
C. To oxidize organic compounds prior to digestion
D. To precipitate interfering metal ions out of solution
CORRECT ANSWER: B. To preserve the sample by lowering the pH to less than 2
and halting biological activity
Rationale: Acidifying the COD sample with sulfuric acid to a pH of less than or equal
to 2 inhibits microbial degradation of the organic matter, ensuring the sample
remains representative until laboratory analysis can be performed.
Question 3: In a standard spectrophotometric determination, what law states that
absorbance is directly proportional to the concentration of the absorbing species in
the solution?
A. Henry's Law
B. Boyle's Law
Page 2 of 165
,C. Beer-Lambert Law
D. Dalton's Law
CORRECT ANSWER: C. Beer-Lambert Law
Rationale: The Beer-Lambert Law establishes the linear relationship between
absorbance and concentration, which is the foundational principle underlying most
colorimetric and spectrophotometric wastewater analyses.
Question 4: When performing a total suspended solids (TSS) analysis, what is the
standard drying temperature range for the glass-fiber filter and residue?
A. 103 to 105 degrees Celsius
B. 179 to 181 degrees Celsius
C. 540 to 560 degrees Celsius
D. 99 to 100 degrees Celsius
CORRECT ANSWER: A. 103 to 105 degrees Celsius
Rationale: Drying the filter at 103 to 105 degrees Celsius evaporates all
uncombined moisture without volatilizing or decomposing the organic fraction of the
suspended solids.
Question 5: Which piece of glassware is calibrated to contain a precise volume at a
specific temperature and is used for preparing standard solutions?
A. Erlenmeyer flask
B. Volumetric flask
C. Graduated cylinder
D. Beaker
CORRECT ANSWER: B. Volumetric flask
Rationale: Volumetric flasks are Class A glassware specifically designed to contain
an exact, certified volume of liquid when filled to the calibration mark, making them
essential for accurate standard solution preparation.
Question 6: What safety equipment should always be used when handling
concentrated acids and strong bases in a laboratory setting?
A. Chemical splash goggles, face shield, and chemical-resistant gloves
B. Standard prescription eyeglasses and cotton lab coat
C. Heat-resistant leather gloves and ear protection
D. Dust mask and latex examination gloves
Page 3 of 165
, CORRECT ANSWER: A. Chemical splash goggles, face shield, and chemical-
resistant gloves
Rationale: Concentrated acids and bases pose severe splash and corrosion
hazards, requiring comprehensive eye, face, and hand protection such as splash
goggles, a full-face shield, and heavy-duty chemical-resistant gloves.
Question 7: In the Winkler titration method for dissolved oxygen, what titrant is
commonly used to titrate the liberated iodine?
A. Silver nitrate
B. Sodium thiosulfate
C. Hydrochloric acid
D. Sodium hydroxide
CORRECT ANSWER: B. Sodium thiosulfate
Rationale: Sodium thiosulfate is the standard titrant used in the iodometric Winkler
method, reacting stoichiometrically with the free iodine released during the multi-
step chemical fixation process.
Question 8: What is the primary hazard associated with the digestion step of the
Chemical Oxygen Demand (COD) test using potassium dichromate and
concentrated sulfuric acid?
A. Production of explosive hydrogen gas
B. Extreme exothermic reaction and high pressure buildup in sealed vessels
C. Rapid volatilization of toxic carbon monoxide gas
D. Immediate precipitation of toxic lead compounds
CORRECT ANSWER: B. Extreme exothermic reaction and high pressure buildup in
sealed vessels
Rationale: Mixing concentrated sulfuric acid with water and organic samples
generates intense heat, and closed-vessel digestion creates significant pressure,
requiring proper containment, shielding, and safety glasses.
Question 9: Which microbial indicator group is traditionally used in wastewater
laboratories to assess the bacteriological safety and sanitary quality of treated
effluents?
A. Coliform group
B. Nitrifying bacteria
C. Sulfate-reducing bacteria
Page 4 of 165
