A Glass rod, stirring rod or stir rod is a piece of laboratory equipment used to mix chemicals and liquids for laboratory purposes. They are usually made of solid glass, about the thickness and slightly longer than a drinking straw, with rounded ends. Like most laboratory glass, stir rods are made of borosilicate (commonly known as pyrex).
A stirring rod is used for mixing liquid. It can help decant the liquid from a container while the solid still remains in the flask. It is easier to keep a precipitate from the bottom of the beaker as it decreases the chances of solid agitation. By pouring it slowly, it is important especially when dealing with potentially dangerous chemicals reacting very quickly. Moreover, it can induce crystallization in a recrystallization procedure. The glass rod is scraped when there is the solution containing inside the flask. It also helps break up an emulsion in an extraction.
Techniques of Using Stirring Rod
- The preparation of using stirring rods is to cut short lengths of thin glass rod and fire polish the two ends.
- When getting wet, clean it in every usage, or the next solution will get contaminated.
- When done with each use, place it in a beaker of clean distilled water and swirl.
- If possible, keep changing water so as to avoid contamination as much as possible.
Applications in Physics
Vanishing rods experiment
In Physics, there is an experiment called "Vanishing Rods". It is the experiment that people have to fill the jar with tap water of approximately half way up. Then, put two glass rods into the water, look it through the jar and notice. Subsequently, fill another jar full with the Wesson Oil half way full, then put the Pyrex glass rods in, look through and notice. According to index of refraction, it can make the rod disappear when being with the oil. Another jar with Wesson oil makes the rods disappear from looking through. The index of refraction is the measure of how fast the light travels through the material. If the light passes from one material to another, the light is bent. This means that the two materials have discrepant indexes of refraction. Similarly, when glass and air are together and light shines through, the light bends a little at the surface: this makes the two materials seen as being separated. This is why people can see the glass rod in the air. In another case, if the two indexes of refraction are not too different, the light will not bend too much. When the Pyrex rods are in water, people still see them clearly. This is because the index of refraction of Pyrex and water are a bit distinct. When the Pyrex rods are put into the oil, the rods are disappeared as the oil has the same index of refraction as the Pyrex rod, which makes the light not bend at the surface of the glass.
- Electrification by friction occurs when there are two surfaces rubbing together. For instance, rubbing glass with silk gives positive charge and rubbing rubber with fur gives negative charge. A larger portion of the triboelectric sequence is as follow:(greatest) Asbestos, Fur (rabbit) ,Glass, Mica, Wool, Quartz, Fur (cat), Lead, Silk, Human skin, Aluminum, Cotton, Wood, Amber, Copper, Brass, Rubber, Sulfur, Celluloid, and India rubber(lowest). To give more details, rubbing glass rod with silk, it creates positive or vitreous charges. This means the rod loses electrons, and in the other way round, the silk gets electrons, meaning a negative charge. Therefore, the glass rod and silk remain the net charge of zero, in other words, the electric charge is conserved. Negative or resinous charge is created when rubbing a rubber rod with fur. The rod is charged negatively and the fur positively. Note that the positive charge gives the particle a charge of +1.6 x 10−19 coulombs, whilst the negative charge -1.6 x 10−19 coulombs.
- Conduction is another mode of electrification. Conduction occurs when the charging rod touches the electroscope’s knob. Because of being in contact, electrons from the knobs will be positive. It leaves the electrosope with a residual charge, similarly to charging rod.
- Charging by induction means charging rod never touch electroscope’s knob, which gives the charging redistribution will be positively charged.
How to Make Stirring Rod
- Glass working of borosilicate is made with the torches with high temperature. For the rounding end, use a plain propane plumbing by holding it in the vertical way in the flame. After some time, it has become liquid sufficiently to ball up.
- Then, people have to repeat this for the other end. Next, people have to locate the cooled one at the center and create a mark. Place the rod on the surface hard enough to use the saw. Saw it with the edge of the file perpendicular to the rod until a small notch is made. While sawing, slowly rotate the rod by using the notch and then, wrapping a towel around the rod.
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