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Quiz & test questions Grade 9 Careers & CTE

Osterlin Water Lab: A Water Quality Analyst Certification Quiz

A 40-point grade 9 careers quiz on the laboratory analyst's job at a fictional certified water lab, covering titrations, dilutions, quality control, and custody records.

Objectives

  1. Students will distinguish the laboratory analyst's duties from the plant operator's duties.
  2. Students will calculate alkalinity, dilution-corrected results, and relative percent difference from stated laboratory data.
  3. Students will judge whether a sample meets holding time, quality control, and chain of custody requirements.

Vocabulary

Alkalinity
Alkalinity is water's ability to resist becoming acidic, acting like a buffer that keeps pH from swinging wildly when acids are added. Water with good alkalinity helps protect fish and other aquatic life from sudden pH changes.

Also: chain of custody, holding time, relative percent difference, reporting limit, dilution factor

Teacher overview

This quiz closes the unit on laboratory work in a water utility, the career path students meet when they ask who actually produces the numbers an operator acts on. It is worth 40 points across 14 items, mixing multiple choice, short answer, and calculation, and it runs about 50 minutes with a calculator. All items use the fictional Osterlin Regional Laboratory so that one set of methods and limits carries through the quiz. Teaching note: students commonly believe a laboratory result is wrong only when the arithmetic is wrong, so they accept a result that reached the bench two days past its holding time. Items 9, 10, and 14 exist to make the point that a defensible result depends on the record as much as the bench work, and an analyst who cannot show custody has no usable number.

Osterlin Water Lab: A Water Quality Analyst Certification Quiz — Grade 9 Careers & CTE
Name: ____________________________ Date: ______________

Assessment

Use the following information about the fictional Osterlin Regional Laboratory for every item. Show your work and write the unit beside every number you calculate.

  • Chlorine demand equals the dose applied minus the residual measured, both in milligrams per liter.
  • Alkalinity in milligrams per liter as calcium carbonate equals the milliliters of acid used, times the acid's normality, times 50,000, divided by the milliliters of sample titrated.
  • A dilution factor is the final volume divided by the volume of sample taken. The reported result is the measured result times the dilution factor.
  • Relative percent difference between duplicate results equals the difference between them, divided by their average, times 100. Osterlin accepts duplicates at 10 percent or below.
  • Osterlin's reporting limit for nitrate is 0.5 mg/L. Any result below the reporting limit is reported as less than that limit rather than as a number.
  • The holding time for a total coliform sample is 30 hours from collection to analysis.
  • Osterlin's chain of custody form must carry five entries: the sample identification, the collection date and time, the collector's name, the preservative used, and a signature at every transfer of the sample.
  • The client utilities Osterlin serves keep chlorine residual in distribution between 0.2 and 2.0 mg/L.
  1. Which task belongs to the laboratory analyst rather than to the treatment plant operator? (2 points)
    A. Adjusting the chemical feed pump when the residual drifts low
    B. Running a standard and a blank before analyzing the day's samples
    C. Backwashing a filter at the end of its run
    D. Exercising a valve on a distribution main
  2. Osterlin analyzes drinking water samples used for compliance. Which statement about laboratory certification is accurate? (2 points)
    A. Any laboratory may report compliance results as long as an operator signs the form.
    B. The laboratory must hold state certification for each method it uses for compliance samples, and analysts work to written methods that the certification covers.
    C. Certification applies to the analyst personally and moves with that person to any employer.
    D. Certification is required only for samples that fail.
  3. A utility applies a chlorine dose of 2.4 mg/L and measures a residual of 0.8 mg/L. Calculate the chlorine demand. (3 points)
  4. A distribution sample arrives with a chlorine residual of 0.14 mg/L. State whether that result falls inside the range client utilities maintain, which is 0.2 to 2.0 mg/L. (2 points)
  5. An analyst titrates 100 mL of sample and uses 14.2 mL of acid at a normality of 0.02. Using the alkalinity formula above, calculate the alkalinity in milligrams per liter as calcium carbonate. (4 points)
  6. A sample is diluted by taking 20 mL of sample and bringing it to a final volume of 100 mL with reagent water. The diluted sample measures 18 mg/L. Calculate the result the analyst reports for the original sample. (4 points)
  7. Duplicate analyses of one sample give 24.6 mg/L and 26.2 mg/L. Using the relative percent difference formula above, calculate the relative percent difference. (4 points)
  8. A different duplicate pair gives a relative percent difference of 12.4 percent. State whether that pair meets Osterlin's acceptance limit of 10 percent. (2 points)
  9. A total coliform sample is collected at 9:00 in the morning and reaches the analyst's bench at 11:30 that night. Calculate the elapsed time in hours. (3 points)
  10. The holding time for that sample is 30 hours. State whether the sample described in item 9 was analyzed inside its holding time. (2 points)
  11. A nitrate analysis computes to 0.32 mg/L, and Osterlin's reporting limit for nitrate is 0.5 mg/L. State how the analyst must report this result. (3 points)
  12. A client's raw water tests at 214 mg/L total hardness as calcium carbonate, and the utility's softening goal is 120 mg/L. Calculate the hardness that must be removed. (3 points)
  13. Using the same raw hardness of 214 mg/L and the same goal of 120 mg/L, calculate the percent of the hardness that must be removed. (3 points)
  14. A chain of custody form arrives showing the sample identification, the collection date and time, the preservative used, and the receiving analyst's signature. Using Osterlin's five required entries above, state what is missing. (3 points)

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: B.
    Running a standard and a blank before the day's samples is bench quality control, which belongs to the analyst. The other three choices are operations tasks performed at the plant or in the street.
  2. Answer: B.
    A laboratory holds certification method by method for compliance work, and analysts follow the written methods that certification covers. Certification belongs to the laboratory rather than to a person, and it applies to every compliance sample, not only to failures.
  3. Answer: 1.6 mg/L.
    Chlorine demand equals dose minus residual, so 2.4 mg/L minus 0.8 mg/L equals 1.6 mg/L.
  4. Answer: No.
    A residual of 0.14 mg/L is below the lower end of the 0.2 to 2.0 mg/L range, so the sample falls outside it and the utility would flush and resample.
  5. Answer: 142 mg/L.
    Multiply the titrant volume, the normality, and 50,000, then divide by the sample volume. First, 0.02 times 50,000 equals 1,000. Then 14.2 mL times 1,000 equals 14,200, and 14,200 divided by 100 mL equals 142 mg/L as calcium carbonate.
  6. Answer: 90 mg/L.
    The dilution factor is the final volume divided by the sample volume, so 100 mL divided by 20 mL equals 5. Then 18 mg/L times 5 equals 90 mg/L in the original sample.
  7. Answer: 6.3 %.
    The difference is 26.2 minus 24.6, which is 1.6 mg/L. The average is 24.6 plus 26.2 divided by 2, which is 25.4 mg/L. Then 1.6 divided by 25.4 equals 0.063, and times 100 gives 6.3 percent.
  8. Answer: No.
    A relative percent difference of 12.4 percent is larger than the 10 percent limit, so the pair fails the check and the analyst reruns the sample rather than reporting the average.
  9. Answer: 14.5 hours.
    From 9:00 in the morning to 9:00 at night is 12 hours, and 9:00 at night to 11:30 at night adds 2.5 hours, giving 14.5 hours.
  10. Answer: Yes.
    An elapsed time of 14.5 hours is less than the 30-hour holding time, so the result may be reported.
  11. Answer: Less than 0.5 mg/L.
    The computed value of 0.32 mg/L sits below the reporting limit, so the analyst reports it as less than 0.5 mg/L rather than as a number the method cannot support.
  12. Answer: 94 mg/L.
    Subtract the goal from the raw value: 214 mg/L minus 120 mg/L equals 94 mg/L of hardness to be removed.
  13. Answer: 43.9 %.
    Divide the amount removed by the starting amount and multiply by 100. The amount removed is 214 minus 120, which is 94 mg/L. Then 94 divided by 214 equals 0.439, and times 100 gives 43.9 percent.
  14. Answer: The collector's name and the collector's signature.
    The form shows the identification, the date and time, the preservative, and the receiving signature. Osterlin requires the collector's name and a signature at every transfer, so the collector's name and the collector's signature at the point of handoff are both absent.

Differentiation

Support

Give these students a formula card carrying the alkalinity, dilution factor, and relative percent difference formulas with one worked example each from the fictional Osterlin methods. Allow them to answer items 1, 2, 4, 8, 10, and 14 first, which test the analyst's judgment rather than the arithmetic. On item 5, write the product 0.02 times 50,000 in for them, since that step is where most errors start.

Extension

Ask these students to write the corrective action memo an analyst at the fictional Osterlin laboratory would send after the failed duplicate in item 8, naming what is rerun, what the client is told, and when. Then have them calculate the alkalinity that 21.3 mL of the same 0.02 normal acid would indicate on a 100 mL sample and state what a rise of that size would suggest about the source water.

ELL supports

Pre-teach chain of custody, holding time, duplicate, reporting limit, and dilution factor using a labeled photograph or sketch of a sample bottle, a cooler, and a custody form. Provide a bilingual glossary card for the five custody entries. Offer a sentence frame for items 4, 8, 10, and 14: "The limit is ___, the result is ___, so the analyst must ___."

Extensions

Have students trace one fictional Osterlin sample from the tap to the report by drawing each handoff and naming who signs at each one. Then ask which single missing entry would make the result unusable for compliance, and have them defend the choice in two sentences. Custody and handling problems, such as a missing signature or a missed holding time, are a common reason a compliance result has to be discarded.