A gas

syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...

is a piece of laboratory glassware used to insert or withdraw a

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). The de ...

of a

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

from a closed system, or to measure the volume of gas evolved from a

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

.Mattson, Bruce. Microscale Gas Chemistry: Determination of the Molar Mass of Gas. Microscale Gas Chemistry. Bruce Mattson, 15 Mar. 2010. Web. 17 Nov. 2011. . A gas syringe can also be used to measure and dispense liquids, especially where these liquids need to be kept free from air.UCLA, comp. Procedures for Safe Use of Pyrophoric Liquid Reagents. Procedures for Safe Use of Pyrophoric Liquid Reagents. UCLA Chemistry & Biochemistry, Sept. 2009. Web. 17 Nov. 2011. . A gas syringe has an inner syringe chamber which has a ground glass surface. The syringe barrel also has a ground glass surface. The ground surface of the barrel moves freely within the ground glass surface of the syringe chamber with very little friction. The close mating of these ground glass surfaces also gives a reasonably gas-tight seal.VICI. "Pressure Lok® Glass Syringe Features." Valco Instruments Company Incorporated. Valco Instruments Company Incorporated, Jan. 2011. Web. 17 Nov. 2011. . Like a ground glass

stopcock A stopcock is a form of valve used to control the flow of a liquid or gas. The term is not precise and is applied to many different types of valve. The only consistent attribute is that the valve is designed to completely stop the flow when clo ...

, the two parts of a gas syringe should preferably not be interchanged with another gas syringe of the same volume, unless told otherwise by the distributor. Gas syringes come in various sizes from 500 ml to 0.25 ml and tend to be accurate to between 0.01 and 1 ml, depending on the size of the syringe.

Gas syringe use

A gas syringe can be used to measure gaseous products from a reaction. When using a gas syringe to measure gases it is important to keep the syringe free from liquids. As gases can dissolve in liquids, especially under any resulting pressure, this may result in inaccurate measurements ( Henry's law). The amount of gas in moles formed in a reaction can be measured by measuring the volume of gas evolved at standard (or known) pressure conditions (

gas law The gas laws were developed at the end of the 18th century, when scientists began to realize that relationships between pressure, volume and temperature of a sample of gas could be obtained which would hold to approximation for all gases. Boyle ...

, PV=nRT). Accordingly, it is important that the syringe barrel should move freely within the syringe chamber, if one assumes that the measured gas is at standard temperature and pressure. Any friction would result in a pressure build-up in the syringe and would lead to an inaccurate measurement, that is, a lower amount of gas would be determined, than really obtained.

Liquid use

Glass syringes are also conveniently used to measure and dispense

solvents A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

and other liquids. They are often used in air-free techniques to take solvents after they have been purified in stills, or from containers sealed with

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five coun ...

, to prevent gas entering the solution. They can also be use for transportation of substances that react spontaneously with air (pyrophoric reagents).Norton, Jack. "The Safe Use of Pyrophoric Reagents." Pyrophoric Reagents. Columbia University, May 2010. Web. 17 Nov. 2011. . Liquids drawn up into a gas syringes can optionally be sparged with inert gas before dispensing into a reaction vessel such as a Schlenk flask. This is done by drawing the liquid into the syringe via a needle, inserting the needle into the septum sealing a flask under a positive pressure of an inert gas, removing the glass plunger, and allowing the gas to bubble through the liquid in the syringe for several minutes. The glass plunger is then re-inserted and the liquid is added to the reaction flask. Other techniques such as cannulation can also be used to transfer liquids instead.

References

{{Laboratory equipment Laboratory glassware