Gas collecting tube
Encyclopedia
The characterization gas collecting tube describes an oblong
gas-tight container with one valve
at either end. Usually such a container has a gauge
d volume
, has a cylindrical shape
and is made of glass
. Gas collecting tubes are used for science-related purposes; for taking samples of gases.
can be measured by using a gas collecting tube, an analytical balance and an aspirator
. The mass and volume of a displaced amount of gas are determined: At atmospheric pressure
, the gas collecting tube is filled with the gas to be investigated and the overall mass 
is measured. Then the aspirator sucks out much of the gas yielding a second overall mass 
measurement. (The difference of masses represents the mass (
) of the extracted amount of gas.) Finally, the nearly evacuated gas collecting tube is allowed to suck in an outgassed liquid, usually previously heated water, which is offered under atmospheric pressure 
. The gas collecting tube is weighed for a third and last time containing the liquid yielding the value 
. (The difference of masses of the nearly evacuated tube and the liquid-containing tube gives the mass (
) of the sucked-in liquid, that took the place of the extracted amount of gas.) The given mass-density 
of the liquid permits to calculate the displaced volume (
). Thus giving mass 
and volume 
of the extracted amount of gas, consequently accessing its mass density (
) under atmospheric pressure
can be measured by using a gas collecting tube, an analytical balance and two other fluids of known mass densities, preferably a gas and a liquid (with mass densities
, 
). Overview: First, mass measurements get the volume 
and the evacuated mass 
of the gas collecting tube; secondly, these two are used to measure and calculate the mass-density 
of the investigated fluid.
Fill the gas collecting tube with one of those fluids of given mass density and measure the overall mass, do the same with the second one giving the two mass values
, 
. Consequently for those two fluids, the definition of mass density can be rewritten:
These two equations with two unknowns
and 
can be solved by using elementary algebra:
(The relative error of the result significantly depends on the relative proportions of the given mass densities and the measured masses.)
Now fill the gas collecting tube with the fluid to be investigated. Measure the overall mass
to calculate the mass of the fluid inside the tube 
yielding the desired mass density 
.
(and not a mixture), with the mass density
, then using the ideal gas law
permits to calculate the molar mass
of the gaseous chemical substance: 
(
represents the universal gas constant, 
the absolute temperature at which the measurements took place)
Rectangle
In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...
gas-tight container with one valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
at either end. Usually such a container has a gauge
Gauge (engineering)
In engineering, a gauge or gage, is used to make measurements. A wide variety of tools exist which serve such funtions, ranging from simple pieces of material against which sizes can be measured to complex pieces of machinery...
d volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
, has a cylindrical shape
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
and is made of glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
. Gas collecting tubes are used for science-related purposes; for taking samples of gases.
Measurement of the Mass Density of a Gas - Aspirator Method
The mass density of a gasGas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
can be measured by using a gas collecting tube, an analytical balance and an aspirator
Aspirator
An aspirator, also called an eductor-jet pump or filter pump, is a device that produces vacuum by means of the Venturi effect. In an aspirator, fluid flows through a tube which then narrows. When the tube narrows, the fluid's speed increases, and because of the Venturi effect, its pressure...
. The mass and volume of a displaced amount of gas are determined: At atmospheric pressure
, the gas collecting tube is filled with the gas to be investigated and the overall mass is measured. Then the aspirator sucks out much of the gas yielding a second overall mass measurement. (The difference of masses represents the mass () of the extracted amount of gas.) Finally, the nearly evacuated gas collecting tube is allowed to suck in an outgassed liquid, usually previously heated water, which is offered under atmospheric pressure . The gas collecting tube is weighed for a third and last time containing the liquid yielding the value . (The difference of masses of the nearly evacuated tube and the liquid-containing tube gives the mass () of the sucked-in liquid, that took the place of the extracted amount of gas.) The given mass-density of the liquid permits to calculate the displaced volume (). Thus giving mass and volume of the extracted amount of gas, consequently accessing its mass density () under atmospheric pressureMeasurement of the Mass Density of a Gas - Two Fluid Method
The mass density of a fluidFluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
can be measured by using a gas collecting tube, an analytical balance and two other fluids of known mass densities, preferably a gas and a liquid (with mass densities
, ). Overview: First, mass measurements get the volume and the evacuated mass of the gas collecting tube; secondly, these two are used to measure and calculate the mass-density of the investigated fluid.Fill the gas collecting tube with one of those fluids of given mass density and measure the overall mass, do the same with the second one giving the two mass values
, . Consequently for those two fluids, the definition of mass density can be rewritten:These two equations with two unknowns
and can be solved by using elementary algebra:(The relative error of the result significantly depends on the relative proportions of the given mass densities and the measured masses.)
Now fill the gas collecting tube with the fluid to be investigated. Measure the overall mass
to calculate the mass of the fluid inside the tube yielding the desired mass density .Molar Mass from the Mass Density of a Gas
If the gas is a pure gaseous chemical substanceChemical substance
In chemistry, a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e. without breaking chemical bonds. They can be solids, liquids or gases.Chemical substances are...
(and not a mixture), with the mass density
, then using the ideal gas lawIdeal gas law
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation to the behavior of many gases under many conditions, although it has several limitations. It was first stated by Émile Clapeyron in 1834 as a combination of Boyle's law and Charles's law...
permits to calculate the molar mass
Molar mass
Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...
of the gaseous chemical substance: ( represents the universal gas constant, the absolute temperature at which the measurements took place)External links
- Source of the notion "gas collecting tube", among others http://www.wilmad-labglass.com/group/1264