1. Preparation of nitrobenzene
After mixing concentrated nitric acid and concentrated sulfuric acid, it is necessary to cool them down before adding benzene dropwise to avoid nitric acid decomposition and benzene evaporation. The reaction is carried out in a water bath at 50-60℃. Excess nitric acid and sulfuric acid dissolve in water, while the yellow oily liquid that accumulates at the bottom of the beaker is nitrobenzene, which has a strong bitter almond odor. To prevent benzene evaporation, the test tube opening needs to be covered with a long glass conduit that functions as a condenser tube. In addition, sulfuric acid acts as both a catalyst and a dehydrating agent in this reaction.

2. Calculation of molecular formula of organic compounds using the line-notation method
For linear organic compounds, the number of carbons can be determined by counting the corners and ends. For example, a straight line has two carbons at both ends, and if there is a corner, add one more carbon. At the same time, the number of hydrogens can be calculated by counting the number of lines on the carbon, that is, "to find hydrogen, subtract four from the number of lines". For example, if the carbon in the middle of propane has two lines, 4-2=2, then there are two hydrogens on the carbon. For structures such as cyclopropane, a similar method can be used for calculation.

3. Balancing chemical equations using the observation method
When balancing chemical equations, one can use hydrogen or oxygen as a standard, and determine the balancing coefficients based on the transformation of single and double bonds. For example, if there is hydrogen, use hydrogen as the standard; if there is no hydrogen, use oxygen as the yardstick; if neither hydrogen nor oxygen is present, find a monovalent element for balancing. Through observation, chemical equations can be balanced quickly and accurately.

4. Important experimental phenomena
When hydrogen burns in chlorine, a pale flame is produced; when phosphorus burns in chlorine, smoke fills the air. When methane, hydrogen, and chlorine are mixed, strong light exposure may pose a danger. On the other hand, the combustion of magnesium strip in carbon dioxide and the white smoke emitted when two acids meet ammonia are noteworthy experimental phenomena. Furthermore, the sublimation of ammonium chloride when heated and the blue color change when iodine meets starch are also of considerable observational value. Meanwhile, the combustion of sulfur, hydrogen, methane, and carbon monoxide all produce a blue flame. When copper wire is inserted into sulfur vapor and then mixed with hot iron, a black substance is produced. It is worth noting that when hot copper and hot iron react with chlorine, the smoke produced has a similar color, both being brown.

5. Electrolysis law
During the electrolysis process, if inert materials are used as electrodes and direct current is applied across the two electrodes, then during the electrolysis of oxyacids, soluble bases, and oxy salts of active metals, water is actually being electrolyzed. For non-oxyacids, their electrolysis leads to their own decomposition, with the pH value of the solution increasing and the concentration decreasing. When electrolyzing oxy salts of active metals, the corresponding base is obtained at the cathode; for oxy salts of non-active metals, the salt-forming element is observed at both electrodes. Additionally, during the electrolysis of oxy salts of non-active metals, the corresponding acid is obtained at the anode. In the electrolysis process, oxidation occurs at the anode, while reduction occurs at the cathode.