which of the following operations exists insecurity?
which of the following operation is correct?
for personal safety protection, which of the following practices is wrong?
which of the following treatment methods is correct for the waste liquid produced by the experiments?
which of the following operation is wrong?
what kind of gloves should be used when assembling and disassembling glass instruments?
when the clothes are on fire during the experiment, which of the following operations is wrong?
which of the following operation is wrong?
chemicals in laboratory must be labeled with their names to avoid misuse.
when using the fire extinguisher to extinguish the fire, the nozzle of the fire extinguisher shall be aligned with the middle of the flame.
during the chemical experiment, contact lenses can be worn to protect the eyes.
during the experiment, you can extend your head into the fume hood so that you can see clearly and operate flexibly.
chemicals and laboratory instruments should not be placed at the exit of the fume hood to avoid danger.
myopia mirror can play a reliable protective role, so it is not necessary to wear goggles outside during the experiment.
eyewashes should be checked regularly to ensure that the water pressure is sufficient and water is ejected during use.
you can wear sneakers with mesh to enter the laboratory.
during the experiment, students with long hair must tie their hair.
during the experiment, when you have a minor cut, you should forcefully wash the wound with soap and water for a few minutes, and squeeze the blood out.
when the fire on the body is extinguished, the clothes sticking to the skin should be taken off immediately.
in the event of a fire, cover your nose with a dry towel to avoid being oked.
which kind of injector must be used in liquid chromatography?
how many times should the buret be rinsed with titrant at least after it is rinsed with deionized water?
ultraviolet-visible spectrophotometer generally consists of light source, ( ), sample chamber and detector.
the light source of the ultraviolet-visible spectrophotometer can be ( ) or deuterium lamp.
when turning on the gas chromatograph, you should first
which can be used as the detector of high performance liquid chromatography?
what substances are gas chromatography used to separate and detect?
what parts does the gas chromatograph include?
after the buret is filled with the solution, read immediately.
in parallel titration, the liquid level of the titrant must be adjusted to the same scale level before each titration.
when accurately weighing the primary standard, which of the following balances should be used?
in the titration ysis experiment, the more the amount of indicator, the more obvious the color change, and the less the amount of indicator, the less the color change at the end point.
which of the following solutions must be filled in a brown reagent bottle?
the accurate concentration of kmno4 can be calibrated with na2c2o4 as the primary standard.
which one of the following is commonly used as the primary standards?
the concentration of the edta standard solution should keep four significant digits. which of the following expressions is correct?
when the standard addition method is used for the determination of fluorine content, which of the following descriptions is wrong?
which of the following results may occur by increasing the flow rate of carrier gas in gas chromatography?
which of the following results may occur by increasing the column temperature in gas chromatography?
the detector that can be used for high performance liquid chromatography is ( )
what is the purpose of rinsing the syringe in the liquid chromatographic experiment?
high pressure, high efficiency and high speed are the characteristics of modern liquid chromatography. what is the main cause of high pressure?
which substances are used for separation and detection by gas chromatography?
in order to avoid the loss of stationary phase in liquid chromatography, it indicates the aller the better on the polarity difference between the mobile phase and the stationary phase.
since boric acid is a weak acid, it must be converted into a strong acid before titration. which of the following can react with boric acid to form a strong acid?
because the rate of coordination reaction is very fast, the titration speed can be very fast, and even the solution can be connected into a line.
when using the ion exchange column, pay attention that the liquid level should not be lower than the resin, otherwise bubbles will appear in the exchange column.