Distillation operation is a commonly used experimental technique in chemical experiments

 Distillation operation is a commonly used experimental technique in chemical experiments, which is generally used in the following aspects:

Buy labware from JIANGJING

Steam distillation

(1) Separate the liquid mixture, and only when the boiling point of each component in the mixture has a large difference, can the separation be more effective;

(2) Determine the boiling point of pure compounds;

(3) Purification, to improve the purity of substances containing a small amount of impurities through distillation;

(4) Recover the solvent, or evaporate part of the solvent to concentrate the solution. Steps

Feeding: Pour the distilled liquid carefully into the distillation flask through the glass funnel, taking care not to let the liquid flow out of the branch pipe. Add a few grains of boiling aid, and install a thermometer, which should be installed at the side port leading to the condenser. Check once again whether the connections of all parts of the instrument are tight and proper.

Heating: When water is used in the condenser tube, the cold water is slowly introduced from the lower mouth of the condenser tube, and the water flows out from the upper mouth to the water tank, and then starts heating. When heating, you can see that the liquid in the distillation flask gradually boils and the vapor gradually rises. The thermometer reading also rose slightly. When the top of the vapor reaches the mercury bulb of the thermometer, the thermometer reading rises sharply. At this time, you should properly adjust the flame of the small gas lamp or reduce the voltage of the heating electric furnace or the heating mantle, so that the heating speed is slightly slowed down, and the top of the steam stays in place, so that the upper part of the bottleneck and the thermometer are heated, so that the temperature of the droplets and steam on the mercury ball reaches

Distillation flask

balance. Then increase the flame a little bit to distill. Control the heating temperature and adjust the distillation speed, usually 1 to 2 drops per second. During the whole distillation process, there should be condensed droplets on the mercury bulb of the thermometer. The temperature at this time is the temperature at which the liquid and vapor are in equilibrium, and the reading of the thermometer is the boiling point of the liquid (distillate). The heating flame during distillation should not be too large, otherwise it will cause overheating in the neck of the distillation flask, so that part of the liquid vapor will be directly exposed to the heat of the flame, so that the boiling point read by the thermometer will be higher; on the other hand, distillation is also Do not proceed too slowly, otherwise the boiling point read on the thermometer is low or irregular because the mercury ball of the thermometer cannot be fully infiltrated by the distillate vapor.

Observe the boiling point and collect the distillate: Before distillation, at least two receiving bottles must be prepared. Because before reaching the boiling point of the expected substance, the liquid with a lower boiling point is steamed out first. This part of the distillate is called the "front cut" or "distillation head". After the first distillate is steamed and the temperature stabilizes, the steamed substance is purer. At this time, a clean and dry receiving bottle should be replaced to accept it. Note the reading of the thermometer when this part of the liquid starts to distill and the last drop, namely Is the boiling range (boiling point range) of the fraction. Generally, the liquid contains more or less high-boiling impurities. After the required distillate is evaporated, if the heating temperature is increased, the reading of the thermometer will increase significantly. If the original heating temperature is maintained, it will not If the distillate is evaporated, the temperature will drop suddenly. At this time, the distillation should be stopped. Even if the impurity content is very small, do not evaporate it to avoid rupture of the distillation flask and other accidents.

After the distillation is completed, the heating should be stopped first, then the water supply should be stopped, and the instrument should be removed. The order of dismantling the instrument is opposite to the order of assembling. First remove the receiver, then remove the tail pipe, condenser, distillation head and distillation flask.

Precautions

Pay attention when operating

(1) Put a small amount of broken porcelain pieces in the distillation flask to prevent the liquid from bumping.

(2) The position of the mercury bulb of the thermometer should be on the same horizontal line as the lower end of the branch pipe.

(3) The liquid contained in the distillation flask cannot exceed 2/3 of its volume, nor less than 1/3.

(4) The cooling water in the condenser tube enters from the lower port and exits from the upper port.

(5) The heating temperature cannot exceed the boiling point of the highest boiling substance in the mixture.

Attentions and precautions Attentions and precautions During the distillation operation, the following points should be noted:

(1) Control the heating temperature. If a heating bath is used, the temperature of the heating bath should be several degrees higher than the boiling point of the distilled liquid, otherwise it is difficult to distill the distillate out. The more the heating bath temperature is higher than the boiling point of the distilled liquid, the faster the distillation speed. However, the temperature of the heating bath should not be too high, otherwise the vapor pressure of the distillation flask and the upper part of the condenser will exceed the atmospheric pressure, which may cause accidents, especially when distilling low-boiling substances. Generally, the temperature of the heating bath cannot be higher than the boiling point of the distilled substance by 30°C. During the whole distillation process, add bath liquid at any time to keep the liquid level of the bath liquid at least one centimeter above the liquid level in the bottle.

(2) When distilling high-boiling substances, because it is easy to be condensed, the vapor is often condensed before reaching the side tube of the distillation flask and drips back into the distillation flask. Therefore, short-necked distillation flasks should be used or other insulation measures should be adopted to ensure smooth distillation.

(3) Before distillation, it is necessary to understand the boiling point and saturated vapor pressure of the substance to be distilled and its impurities to determine when (that is, at what temperature) the distillate is collected.

(4) The distillation flask should be a round bottom flask. The liquid with a boiling point of 40-150°C can be a liquid above 150°C, or a simple distillation that is thermally unstable and atmospheric although the boiling point is below 150°C. For liquids with constant boiling points and easy thermal decomposition, vacuum distillation and steam distillation can be used.

Distillation chemistry formula

The heating and cold pipes of the screen are inclined, and the upper and lower edges are flat.

Need to add broken porcelain to prevent violent boiling, hot air and cold water reverse.

Master the liquid limit of the bottle, first withdraw the alcohol and then stop the water. [4]

Related explanation

①Inclination of the cold pipe for heating through the grid: "cold pipe" refers to the condensing pipe. This means that the asbestos net should be separated when heating the distillation flask (to prevent the distillation flask from rupturing due to uneven heating), and the condenser should be tilted downward when installing the condenser.

②The upper edge and the lower edge are flat: it means that the upper edge of the mercury bulb of the thermometer should be exactly on the same horizontal line as the lower edge of the distillation flask branch pipe interface.

③Reverse flow of hot air and cold water: It means that the cooling water must flow continuously from bottom to top, opposite to the direction of the flow of hot steam.

④Master the liquid limit in the bottle: It means that the liquid limit in the distillation flask must be mastered. The maximum volume of the distillation flask should not exceed 2/3, and the minimum should not be less than 1/3.

⑤Remove the alcohol and the water before stopping: It means that when the distillation is over, the fire should be stopped first and then the cooling water should be stopped.