Bench chemistry involves traditional experiments and demonstrations using basic equipment like test tubes, flasks, and a Bunsen burner. Benchtop chemistry techniques include analytical methods like titration, gravimetric analysis, flame tests, and borax bead tests. Over-the-counter methods can also be used to prepare or purify chemical samples. The bench refers to the traditional laboratory workbench, equipped with gas outlets and fume hoods to protect users from toxic gases.
Bench chemistry is the type that is done in the more traditional way: the scientist mixes and handles chemicals directly, using none of the high-tech devices or theoretical approaches that may be associated with the more advanced aspects of the discipline. In essence, these are experiments and demonstrations that can be done with a few chemicals; some test tubes, flasks and glasses; and a Bunsen burner. The stereotypical image of a white-coated scientist pouring chemicals from one test tube to another is a perfect example of over-the-counter chemistry. “Wet chemistry” is sometimes used synonymously with this activity; however, it is an industrial term with a much looser definition and can also refer to the use of high-tech equipment not typically found on a laboratory workbench.
techniques
The term “benchtop chemistry” covers many different scientific techniques that are employed in a laboratory. A general rule of thumb is that if it’s a method that can easily be practiced on a bench without a computer doing most of the calculations and analysis, then it’s a benchtop chemical technique. Analytical methods include titration, gravimetric analysis, flame tests and borax bead tests. Samples of elements or compounds can also be prepared at the workbench. Experimenting, or simply mixing things together to see what happens, is often an over-the-counter activity, and many important discoveries continue to be made this way.
analytical methods
Much of chemistry is about analysis: investigating a sample of material to determine what elements or compounds it contains. While there are instruments, such as spectrometers, that can be used to perform detailed analyses, there are also a wide variety of simple benchtop tests that can be performed by simply mixing a substance or two or by heating something in a Bunsen flame. These procedures may be old-fashioned, but they don’t require expensive equipment and can teach students a lot about chemistry. In the past they have led to important discoveries, such as the discovery of new elements.
Titration, sometimes called volumetric analysis, is a method used to establish the concentration of a dissolved compound. For example, if a chemist wants to know how much hydrochloric acid is present in a solution of water, he can add an alkali solution, such as sodium hydroxide, of known concentration until the resulting solution is neutral. It is therefore possible to calculate the concentration of the hydrochloric acid from the volume of sodium hydroxide solution used.
Gravimetric analysis is based on mass rather than volume and involves weighing the compound or element of interest after isolating it from a sample. For example, to find out how much of a metal is in a mineral, a chemist might first dissolve the mineral in an acid, then add a base that reacts with the metal to form an insoluble compound. This will come out of solution as a fine powder known as a precipitate, which can then be filtered and weighed. It is therefore possible, knowing the atomic weights of the metal and other elements in the precipitated compound, to determine how much metal was present in the mineral.
A flame test is based on the colors produced when certain metals are heated strongly in a Bunsen flame. For example, barium will give green, strontium, red, and cesium, blue. The test is normally performed using a platinum wire with a loop at the end, which is used to take a small amount of sample and introduce it into the flame.
Another way to detect metals is the borax bead test. Still using a loop of platinum wire, a small amount of borax (sodium tetraborate) is melted in a Bunsen flame, then used to take a small amount of sample. This mixture is then re-melted over a flame to form a small round bead. The metals in the sample will produce beads of different colors. The color also depends on which part of the flame the bead is heated in, and the bead can change color as it cools. From the colors produced it is often possible to identify which metal is present.
Preparation of chemical samples
Over-the-counter methods can also be used to prepare or purify samples of particular chemicals. Distillation is a common technique. A mixture of liquids with different boiling points, such as water and ethanol, can be separated by placing it in a flask connected to a condenser, or in a retort, and heating it to a temperature above the boiling point by one, but below the boiling point. boiling point of the other. The liquid with the lowest boiling point is vaporized and can be condensed and collected.
Precipitation is another method that can be used to prepare a chemical that is insoluble in water. For example, a pure sample of calcium carbonate (CaCO3) can be prepared by mixing a solution of a soluble calcium compound — such as calcium chloride (CaCl2) — with a solution of a soluble carbonate — such as sodium carbonate ( Na2CO3), in a glass. The calcium carbonate forms a precipitate at the bottom of the beaker. The other reaction product, sodium chloride (NaCl), which is soluble, could be obtained by evaporation of the remaining liquid. This method can be used to prepare many different compounds.
The bench
Benchtop chemistry gets its name from the traditional laboratory workbench. They are found in both industrial and academic laboratories, and nearly everyone learning the natural sciences will work at one of these desks at one time or another. They are usually resistant to stains, heat and corrosion so that chemical spills and failed experiments do not cause significant damage, and they can be equipped with gas outlets to which a Bunsen burner can be connected. Some workbenches are also surrounded by ventilation systems known as fume hoods to protect users from toxic gases that can be released during certain chemical reactions.
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