What are the types of conductivity electrodes?

Answer: There are two types: bright and platinum black.

Application range of DJS-1 type bright conductivity electrode?

Answer: Used when the conductivity of the solution to be measured is below 10μs/cm.

Applicable range of the "low frequency" of the conductivity meter

Answer: Used when measuring liquids with conductivity below 300μs/cm.

Why should the glass electrode used for measuring PH value be soaked in distilled water before use?

Answer: Because a dry glass electrode does not show the PH effect, only a hydrated glass electrode shows the PH effect, so the glass electrode should be soaked in distilled water for standby.

Why should the glass electrode be treated before use?

Answer: After the glass electrode is soaked for more than 24 hours, a stable hydration layer is formed on the glass electrode, making the membrane potential of the glass electrode linearly related to the PH value of the test solution at a certain temperature. Therefore, the glass electrode should be soaked in distilled water or 0.1N hydrochloric acid for more than 24 hours before use.

Weighing principle of electronic balance?

Answer: The weighing of electronic balance is based on the principle of electromagnetic force balance.

Working principle of PHS-3C type acidity meter?

Answer: It uses a PH electrode and a reference electrode to measure the DC potential generated by different acidity in the solution to be measured, and transmits it to the converter through an amplifier to achieve the purpose of displaying PH.

What is the application range of the 721 type spectrophotometer?

Answer: The 721 type spectrophotometer can be used for quantitative colorimetric analysis in the visible spectral range of 360～800nm in the laboratory.

Precautions for using a spectrophotometer? Answer: The continuous use time should not be too long, the cuvette should be held correctly, the frosted glass surface should be held, the cuvette should be washed and stored properly, and scouring powder or brush should not be used to wash it.

What are the requirements for the working environment of the 721 spectrophotometer?

Answer: It should be placed in a dry room, placed on a firm and stable workbench, away from strong magnetic fields, electric fields and high-frequency wave electrical equipment. Avoid using it in places with corrosive gases such as hydrogen sulfide and sulfurous acid fluoride.

What is the working principle of the 721 spectrophotometer?

Answer: The 721 spectrophotometer is designed according to the Lambert-Beer law A=KCL. When the incident light, absorption coefficient K, and solution path length L are constant, the transmitted light changes according to the concentration.

What are the components of the 721 spectrophotometer?

Answer: It consists of four parts: light source, monochromator, cuvette and detector.

In what environment should the electronic balance be placed?

Answer:

(1) Stable, avoid vibration as much as possible

(2) Ensure no large temperature changes, no corrosion

(3) Avoid direct sunlight and ventilation

(4) The power supply must be stable

Alkaline potassium iodide solution should be stored (in the dark) to prevent (iodine from escaping)

The principle of iodometric determination of dissolved oxygen is that dissolved oxygen combines with manganese sulfate and (sodium hydroxide) to form a brown precipitate of divalent or tetravalent manganese (hydroxide). After adding acid, the precipitate dissolves and undergoes an oxidation-reduction reaction with (iodide ions). The (iodine) equivalent to the dissolved oxygen is released, and then the iodine is titrated with sodium thiosulfate using starch as an indicator to calculate the dissolved oxygen content.

Suspended solids are one of the indicators to measure the quality of wastewater. It can make the water quality (turbid), reduce the water quality (transmittance), and affect the (respiration) and (metabolism) of aquatic organisms.

When measuring CODcr, (potassium hydrogen phthalate) standard solution is used to check the quality of reagents or operation techniques.

The method used in our workshop to measure dissolved oxygen is (iodometric method), which is the (basic method) for determining dissolved oxygen in water.

When measuring the PH of a solution, a (glass electrode) is used as the indicator electrode.

The water sample for measuring suspended solids should be analyzed promptly and should not exceed (12 hours). If the time is long, the suspended solids are easy to (adsorb) to the bottle wall, resulting in low analysis results.

When determining the CODcr value of a water sample, the solution color (turns green) during the reflux process indicates that the organic matter content is (high), and the sample should be re-sampled and analyzed.

When sampling for five-day biochemical oxygen demand, the sampling bottle should be (filled), and (aeration) of the wastewater sample should be avoided as much as possible during sampling and transportation.

When measuring the oil content, the role of anhydrous sodium sulfate is to filter out (trace amounts of water) in the extract.

When titrating iodine with sodium thiosulfate, use an (acid) burette.

The total phosphorus content in circulating water includes (orthophosphate), (total inorganic phosphate) and (organic phosphate)

CODcr reflects the degree of water pollution by (reducing) substances.

COD measurement data should be retained to (three) significant figures.

The W-331 content is directly proportional to the phosphate content in water, with a conversion factor of 14.1.

Industrial circulating cooling water turbidity can be measured using spectrophotometry.

Adding W-331 to the circulating water is an organic phosphorus corrosion inhibitor, which has a corrosion and scale inhibition effect.

Iodometry is a basic method for determining dissolved oxygen in water.

The alkalinity in circulating water mainly includes carbonate, bicarbonate, and hydroxide.

Dissolved oxygen in water is inversely proportional to oxygen consumption.

When measuring oil in water, carbon tetrachloride is used as an extractant.

When measuring calcium ions, EDTA standard solution is used for titration until the yellowish-green fluorescence disappears, and the appearance of red indicates the endpoint.

Microscopic observation can reveal the types and quantities of bacteria in activated sludge, thus judging the treatment effect.

What is biochemical oxygen demand (BOD)?

Answer: It refers to the amount of dissolved oxygen required for the biochemical process of microbial decomposition of organic matter in wastewater under aerobic conditions.

What nutrients are added to the diluted water for five-day BOD?

Answer: Calcium chloride, ferric chloride, magnesium sulfate, and phosphate buffer solution.

What is activated sludge?

Answer: It is mainly formed by the aggregation of a large number of microorganisms growing in wastewater. In addition to microorganisms, activated sludge also contains some inorganic substances and decomposing organic matter.

What indicator is used to measure alkalinity?

Answer: Phenolphthalein indicator and methyl orange indicator.

What is the purpose of measuring the conductivity of pure water?

Answer: Under a certain temperature and a constant flow rate of 0.05 m/s, testing the conductivity of the water sample can determine the purity of the pure water.

What does chemical oxygen demand (COD) refer to?

Answer: Under certain conditions, the amount of oxidant consumed when treating a water sample with a strong oxidant.

What does COD reflect?

Answer: It reflects the degree of water pollution by reducing substances.

What method is specified for COD determination?

Answer: For industrial wastewater, China stipulates the use of the potassium dichromate method.

What are the requirements for COD data processing?

Answer: The results should be retained to three significant figures.

What is the total volume of the solution used for COD titration? Why?

Answer: The total volume should not be less than 140 mL; otherwise, due to excessive acidity, the titration endpoint will not be obvious.

What kind of ion in the water sample is W-331 directly proportional to?

Answer: It is directly proportional to the phosphate content in water, with a conversion factor of 14.1.

What is the basis for selecting an indicator for acid-base titration?

Answer: The principle is that the change range of the acid-base indicator is entirely or partially within the jump range of the titration.

What are the commonly used desiccants at the bottom of the desiccator? Which one can be dried and reused?

Answer: Color-changing silica gel and anhydrous calcium chloride. Color-changing silica gel can be reused.

What is the role of vanadomolybdate in the determination of W-331?

Answer: Vanadomolybdate reacts with orthophosphate to form a phosphovanadomolybdic heteropoly acid complex, which is then determined colorimetrically.

Why is turbidity analysis necessary?

Answer: High turbidity can cause equipment corrosion and scaling, so monitoring is necessary.

What method is used for turbidity analysis, and what are the instrument conditions?

Answer: Spectrophotometry, wavelength 420 nm, 3 cm cuvette.

What is the application range of spectrophotometry for turbidity measurement?

Answer: It is suitable for the determination of turbidity in industrial water circulating cooling water, with a range of 0-45 mg/L.

What is conductivity?

Answer: It refers to the conductance of a solution when the electrode area is 1 cm² and the distance between the electrodes is 1 cm.

What is the principle of calcium hardness determination?

Answer: Calcein can form a yellowish-green fluorescent complex with calcium ions in water. At pH > 12, EDTA standard solution is used to titrate calcium. When approaching the endpoint, EDTA takes away the calcium combined with the indicator, the yellowish-green fluorescence of the solution disappears, and the mixed indicator turns red, which is the endpoint.

What is the principle of pH calibration?

Answer: The known pH value of the solution must be reliable, and the closer its pH value is to the measured value, the better.

What are the standard buffer solutions used for pH measurement in our workshop?

Answer: Three types: pH = 4, pH = 7, pH = 10.

What is the purpose of adding ethanol in the determination of W-331?  

Answer: To stabilize the color-developing solution.

Why is heating and boiling necessary in the determination of W-331?

Answer: To convert all organic phosphates into orthophosphates.

How long should the heating and boiling last in the W-331 determination?

Answer: Boiling time is 30 minutes

W-331 determination principle?

Answer: Using a strong oxidant, potassium persulfate, in a strongly acidic solution, heating and boiling to convert the organic phosphate into orthophosphate, then reacting with ammonium molybdate-vanadate to form a phosphomolybdenum vanadium heteropolyacid complex, and then measuring with a spectrophotometer.

What is turbidity?

Answer: When various dissolved substances or insoluble clays and suspended matter exist in water, it causes turbidity. The numerical representation of this turbidity is called turbidity.

What is dissolved oxygen?

Answer: Oxygen dissolved in water through water-atmosphere exchange or chemical and biochemical reactions is called dissolved oxygen.

What is dissolved oxygen content related to?

Answer: It is related to the partial pressure of oxygen in the air, atmospheric pressure, water depth, and water body state.

How does dissolved oxygen change when algae proliferate in water bodies?

Answer: When algae proliferate, dissolved oxygen can be supersaturated.

What is the impact of organic matter and reducing substances in water bodies on dissolved oxygen?

Answer: Water pollution by organic matter and reducing substances can reduce dissolved oxygen.

Briefly describe the principle of chemical oxygen demand (COD) determination.

Answer: In a strongly acidic solution, a certain amount of potassium dichromate oxidizes the reducing substances in the water sample. The excess potassium dichromate is titrated with ferrous ammonium sulfate solution using ferroin as an indicator. The amount of oxygen consumed by the reducing substances in the water sample is calculated based on the amount used.

In the potassium dichromate method for measuring COD, what are the standard solution indicator added to the sample and the titrating standard solution? Answer:

(1) The standard solution added to the sample is potassium dichromate.

(2) The indicator is ferroin.

(3) The standard solution used to titrate the sample is ferrous ammonium sulfate.

What analytical method is used to measure the oil content in water? What solvent is used?

Answer: Instrumental analysis is used to determine the oil content in water, and the solvent used is carbon tetrachloride.

What water samples is the iodometric method for measuring dissolved oxygen suitable for?

Answer: In the absence of interference, the iodometric method is suitable for water samples with dissolved oxygen concentrations of 0.2-2.0 mg/L.