We all know that concentrated sulfuric acid will release a lot of heat during dilution. Therefore, the correct operation steps should be as shown in Figure 1:
The concentrated sulfuric acid is slowly injected into the water along the wall of the device (the flask is drained with a glass rod), and is continuously stirred, so that the heat generated by dilution can be dissipated in time. The purpose of this is because the density of concentrated sulfuric acid is higher than that of water, and it will float above concentrated sulfuric acid. If the water is added to concentrated sulfuric acid, the water will be heated to boiling in a short period of time when the heat is released in dilute solution, resulting in liquid splashing and accidents. It can be seen that the heat released by concentrated sulfuric acid in the process of dilution is very large, which is the heat released when the solution is diluted. The same solution includes calcium chloride solution, sodium hydroxide solution and so on. Therefore, the operation of this kind of solution in the dilution process should be the same as that of concentrated sulfuric acid dilution. If we don’t know whether the solution to be diluted is endothermic or exothermic in the dilution process, in case of any accident, we should also add unknown solution into the water and stir while adding to prevent accidents.
In the process of solution dilution, the heat is released. In the process of concentration, the concentration of solution increases gradually. Therefore, we need to supplement the heat released in the process of dilution, which is called the heat of concentration. Therefore, when water vapor is used as heating heat source to concentrate the material with heat that cannot be ignored, theoretically, one kilogram of heating vapor will not evaporate one kilogram of secondary steam, because we also need to provide the heat of concentration in the process of material concentration. That is to say, the heating steam needs to provide the latent heat of vaporization from the water in the solution to the secondary steam and the heat of concentration in the process of concentration. The latent heat generated by condensation of heating steam into crystal water is basically the same as the heat required for water to become secondary steam, but the heat of concentration is not enough. In general, we need the enthalpy concentration diagram to calculate the concentration heat needed in the concentration process. However, the enthalpy concentration chart is difficult to find. Many substances will not find the enthalpy concentration chart for a while and a half, so we can roughly estimate the heat of concentration through coefficient adjustment. The concentration coefficient can be taken as 1.1 or 1.2. Figure 2 below is the enthalpy concentration diagram of sodium hydroxide solution for your reference.