CWEA Grade I Laboratory Analyst Exam 2023

CWEA Grade I Laboratory Analyst Exam 2023 Chloride - Major anion found in many natural waters - Can impart salty taste in H2O What increases concentration of chloride in wastewater Chloride in human diet and softeners flushed into sanitary sewer system 2 most prevalent methods of measuring chloride argentometric and mercuric nitrate Argentometric Titration of sample with standard solution of silver nitrate (AgNO3) - Indicator: Chromate ions (CrO4) - End point: reddish silver chromate Mercuric Nitrate Titration with standard mercuric nitrate solution -pH must be adjusted between 2.3 and 2.8 - Indicator: Diphenyl carbazone - End point: Change from blue to purple in presence of mercury Interference of Mercuric Nitrate Method Sulfide, bromide, orthophosphate (over 30 ppm), and iodide Why does color change in water Presence of decaying vegetable matter, metal ions (ie. iron) or industrial and domestic pollution How is color measured Measured using visual comparison method Visual comparison method Sample compared to standards using matched nessler tubes - Standards prepared with solution containing cholorplatinate and cobaltous chloride Standard units for color One unit= color resulting from 1 mg of platinum/L 2 color reporting True and Apparent True color Color from dissolved substances, determine using sample treated to remove turbidity Apparent Color Includes dissolved and suspended solids Conductivity H2Os capability to pass electrical flow Conductivity of pure water 0 Units of conductivity micromhos/cm Temperature conductivity should be read at 25 degrees Celcius How is conductivity affected Mobility of ions, conductivity is dependent on viscosity Viscosity A liquids ability to resist flow, higher the viscosity the lower the flow Relationship of temperature and viscosity Inverse Acid A compound which liberates hydrogen ions and has a pH below 7. Alkalinity: The measurement of a sample's capacity to neutralize acid. Alkalinity measures The carbonate, bicarbonate, and hydroxide ion concentration found in water Primary reason for measuring alkalinity Used in control of many water and wastewater unit processes How is alkalinity measured Titration of a sample with a standard solution of either sulfuric acid or hydrochloric acid to predetermined pH endpoint The phenolphthalein alkalinity of a water sample is zero if: The pH is greater than 8.3 Atomic Weight: The sum of the number of protons and the number of neutrons in the nucleus of an atom. Atomic weights of elements are found on periodic tables. Base: A compound which liberates hydroxide ions and has a pH above 7. Biochemical Oxygen Demand (BOD): The quantity of oxygen utilized in the biochemical oxidation of organic matter under standard laboratory procedures for five days at 20° Centigrade, usually expressed as a concentration (e.g., mg/L). BOD measurements are used to indicate the organic "strength" of wastewater. Chain-of-Custody: A legal record (which may be a series of records) of each person who had possession of an environmental sample, from the person releasing the sample, to the person who collected the sample, to the person who analyzed the sample in the laboratory, to the person who witnessed the disposal of the sample. Chemical Oxygen Demand (COD): The amount of oxygen (expressed in mg/L) consumed from the oxidation of pollutants during a specific test. As such, COD is a measure of the oxygen-consuming capacity of the pollutants present in wastewater. The results of the COD test are not necessarily related to the BOD, because the chemical oxidant responsible for utilizing the oxygen may react with substances which bacteria do not stabilize. Composite Sample: A collection of individual samples obtained at regular intervals, based either on flow or time. The individual samples are combined proportionally. .If you have been given instructions you dont understand Ask the author Mercuric nitrate titration technique for measureing chloride is falling into disuse in the lab because Mercury creates a hazardous waste problem Standard phenylarsine oxide solution (PAO) Should be handled with caution because its is a severe poison Sampling protocol for chloride includes Glass or plastic container with no preservative Incubator temperature for BOD 20 +/- 1 degrees C Laboratory mistakes may be corrected by Lining out the mistake with pen and writing the correct answer to the side of the first, with analysts initials and date The sample receiving log must record time and date sampled Sample collector, nature of sample, analyses to be performed, preservatives, condition of sample and sample recipient Hood flow should be monitored and documented at 100 linear feet per minute Normality equation (N1)(V1)=(N2)(V2) Lauryl Sulfate Broth is sterilized before use for 15 minutes at 121 degrees C Agar medium is used for Heterotrophic plate count During acid base titration, titrant is added to the sample with Buret When preparing diluted calibration standards from a stock standard, use combination of the following to get the most precise standard Class A volumetric flask and class A volumetric pipet At a given temperature, the intensity of the acidic or basic character of a solution is indicated by pH or hydrogen ion activity pH measurement requires the following voltmeter, glass pH electrode, reference electrode, and a temperature compensating device Conductance measurements are temperature compensated to 25 degrees C Conductivity meter is calibrated with 0.0100 N potassium chloride standard Alkalinity is reported as Alkalinity mg CaCO3/L The hardness determination by EDTA titration measures Calcium and magnesium The indicator for the hardness determination is eriochrome Black T EPA acceptable primary standards for the turbidity determination include formazine only BOD determination is an empirical test in which standardized lab procedures are used to determine the relative oxygen requirements of wastewaters, effluents and polluted waters Sample pretreatment for BOD assuring that the samples are neutralized to pH range between 6.5 and 7.5 and any residual chlorine has been dechlorinated Disinfection Process designed to kill most microorganisms in wastewater, including all essentially pathogenic bacteria Fecal coliform bacteria Bacteria found in feces of warm blooded animals Total coliform group All of the aerobic and faculative anaerobic, gram negative, nonspore-forming, rod shaped bacteria that ferment lactose in 24-48 hours at 35 degrees C Lab test results for an individual environmental sample within an analytical batch may be rejected when A known error has occured Precision is measured by Analyzing replicate samples Accuracy The combination of bias and precision of an analytical procedure, which reflects the closeness of a measured value to a true value Bias Consistent deviation of measured values from the true value, caused by systematic errors in a procedure Precision Measures the degree of agreement among replicate analyses of a sample, usually expressed as the standard deviation Random Error Consistent deviation of measured values from the true value, caused by systematic errors in a procedure Total Solids Well mixed sample is evaporated in a weighed dish and dried to constant weight in an oven at 103-105 degrees C Preparing Total solids evaporating dish Ignite clean evaporating dish at 550 furnace for 1 hour and store and cool in desicator Analysis procedure of total solids 1. Choose sample volume that will yield residue between 2.5 and 200 mg 2. Dry evaporated sample for 1 hour in 103-105 degree C oven 3. Cool in desicator and weigh to constant weight Constant weight for total solids