Commonly used glassware in organic chemistry experiments

- Mar 04, 2018-

Common glassware

Each person owns a set of glassware commonly used during experiments, which is usually kept and used personally. Handle glassware gently; no instruments can be heated directly by fire except a few, such as the test tube. Pay attention to the selection and installation of the instrument before conducting the experiment due to the relatively complicated organic reaction and the many varieties and specifications of glassware. Glassware is usually divided into two categories: standard mouth glassware and ordinary glassware.

1. Standard mouth glassware

The standard ground glass instrument typically used in organic experiments is also known as a grinding mouth instrument. It differs from the corresponding ordinary glassware in that each joint is processed into a universal grinding mouth, i.e. a standard grinding mouth. Interior and exterior grinding mouths can be connected to each other tightly, removing the need for a cork or rubber plug. This not only saves the time spent matching plugs, drilling to avoid reactants or products being contaminated by plugs, but also simplifies the assembly and makes washing after disassembly easier. They can also be used for decompression and other operations, greatly improving working efficiency.

Figure 1 the shows commonly used standard ground glass instruments. The standard mouth usually has a serial number such as 10, 14, 19, 24, 29 or 34, which refers to the maximum diameter of the grinding mouth in millimeters.

(1) Pear-shaped flask          (2) Round-bottom flask             (3) Three-necked flask

(4) Thermometer pocket and adjustable stopper        (5) Y-shaped feeding tube      (6) Distilling head

(7) Distilling elbow           (8) Claisen distilling head        (9) Vacuum adapter

(10) Straight condenser pipe     (11) Spherical condenser pipe      (12) Oil-water separator

(13) Constant pressure funnel     (14) Dropping funnel            (15) Drying tube

Figure 1 Common standard mouth glassware

Grinding mouths with different serial numbers cannot be directly connected, but can be connected by the use of a grinding mouth joint (adjustable stopper) with different serial numbers at either end. The size of the adjustable stopper is usually represented by two numbers; for example, 'joint 14 × 19' indicates that one end of the joint is a No. 14 grinding mouth and the other end is a No. 19 grinding mouth. Semi-micro instruments typically have grinding mouths of No. 10 or No. 14; constant volume instruments are numbered above No. 19.

When using standard ground glass instruments, note that the grinding mouth must be clean. Being clogged with solid debris will prevent the butt joint of a grinding mouth from closing, resulting in air leakage or damage to the grinding mouth; after use, the grinding mouth should be promptly disassembled and cleaned, otherwise the jointing parts of the grinding mouth will be cemented and hard to separate. The distilling head will often become stuck to the distilling flask, especially after the distillation of relatively high boiling-point liquids (such as furfuryl alcohol, aniline, etc.); to achieve an extremely high vacuum degree, coat the jointing part of the grinding mouth with a small amount of vacuum grease, which should be promptly removed after use. For general reactions and atmospheric distillation, a grinding mouth does not need lubricants (such as petroleum jelly, vacuum grease, etc.) to avoid the contamination of reactants or products. If there is a strong base in the reaction, lubricant should be applied in order to prevent the jointing part of the grinding mouth from being corroded by alkaline and sticking tightly; be sure to keep everything neat and correct while installing standard ground glass instruments, and align the grinding mouth accurately with the appropriate tightness.

 (A) Flasks: organic reactions are generally carried out in a flask, which often requires heating or cooling outside and generates a relatively long reaction time. In order to meet the needs of the experiment, a variety of flasks are ready for use in the laboratory. For example, the round-bottom flask [see Figure 1 (2)], the neck of which is relatively strong and pressure resistant, is often used in experiments of reflux, distillation and organic reaction, while the pear-shaped flask [see Figure 1 (1)] is applicable to semi-micro operation; if the experiment involves relatively complex operations such as stirring and reflux, a multi-neck flask will be chosen, such as a two-necked flask, three-necked flask or four-necked flask. The three-necked flask [Figure 1 (3)] is also known as a three-mouth flask; its intermediate bottleneck can be installed with an electric mixer and the two side-mouths can be installed with spherical condenser pipes, dropping funnels, thermometers, etc. A three-necked flask installed with a Y-shaped feeding tube [Figure 1 (5)] can replace the four-necked flask. The distillation flask, conventionally used during atmospheric distillation, can be replaced by a round-bottom flask in combination with a distilling head [Figure 1 (6)] or distilling elbow [Figure 1 (7)]. Similarly, the Claisen distillation flask (Claisen flask for short) may be replaced by a round-bottom flask in combination with a Craisen distilling head [Figure 1 (8)]. The Craisen distilling head is commonly used in reduced pressure distillation and distillation prone to producing bubbles or bumping.

 (2) Condenser pipes: the straight condenser pipe is mainly used for the condensation of the distillation and reflux of liquids with relatively high boiling points (over 100℃). If the boiling point of the distillate is below 140℃, pass water into the sleeve for cooling; if it exceeds 140℃, replace the condenser pipe with an air condenser pipe, or a straight condenser pipe if the temperature is not very high, as partial shock cooling in the welding part of the inner tube and sleeve can lead to bursting; the inner tube of the spherical condenser tube has a large cooling area which has a good effect on the condensation of vapor, so the spherical condenser is suitable for reflux operations.

 (3) Funnels: According to the shape, the separating funnel can be divided into cylindrical, round and pear-shaped funnels, which are commonly used for the extraction, washing and separation of liquid and for adding reagents dropwise. If pressure exists in the reaction system, it is preferable to add liquid dropwise with s constant pressure dropping funnel; this not only makes the dropping smooth, but also prevents volatile or toxic vapors from escaping from the upper mouth of the funnel.

 (4) Others: adapters, used to receive distillate during distillation. The single tail adapter is generally used for atmospheric distillation. In order to receive more fractions during reduced pressure distillation, a two-tail or three-tail adapter is often used. While processing anhydrous solvents or using an anhydrous reaction unit, a drying tube is often used in order to avoid moisture, which has an anhydrous calcium chloride inside it as a desiccant; thermowells are used for sealing the thermometer and interfaces.

2. Ordinary glassware

    Although standard ground instruments have become popular in use, they cannot completely replace ordinary glass instruments such as measuring cylinders, beakers, watch glasses, etc. Figure 2 only shows several commonly used types of glassware.

    The Erlenmeyer flask, also known as a conical flask, is commonly used as a receiver during the heating and atmospheric distillation of stock solution and a small amount of solution, as well as in recrystallization operations. Since the bottom of the Erlenmeyer flask is relatively thin and not pressure resistant, do not use this flask for reduced pressure distillation in case it bursts.

    Glass funnels are often used for adding liquids or common filtration; if insulation filtration is needed, use a short-neck funnel or a hot bath funnel. The hot bath funnel is made by installing a copper shell on the periphery of an ordinary glass funnel, putting water between the shell and the funnel and heating the side branch pipe with a gas light to maintain the required temperature.

    The Büchner funnel (generally made of ceramic), in combination with a suction flask, can be used for reduced pressure filtration.

    The Thiele pipe, also known as a b-tube, is normally used to determine the melting point.

    Glassware with relatively thick sidewalls (such as suction flasks) cannot generally be used to heat solutions. After glassware with plugs has been used and washed, put a scrap of paper between the plug and the grinding mouth to prevent sticking. Thermometers with thin-walled mercury balls must not be used as stirring rods and cannot measure the temperature over the scale range. They should be cooled slowly after use and should not be rinsed with cold water immediately to avoid shattering.

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