Density (chemistry): Difference between revisions

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m (→‎Density of substances: Improved second table as well)
imported>Milton Beychok
(→‎Density of substances: Number ed the tables, some copy editing and relocated and clarified the information about gases.)
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{|
{|
|+align="left"|'''Densities of Various Substances'''
|+ align="center"|'''Table 1'''<BR>'''Densities of <BR>Various Substances'''
| '''Substance'''|| '''Density'''<BR>(kg/m³)  
|'''Substance'''|| align="center"|'''Density'''<BR>(kg/m³)  
|-  
|-  
| [[Iridium]]|| 22650
|[[Iridium]]||align="center"| 22650
|-  
|-  
| [[Osmium]]|| 22610
|[[Osmium]]||align="center"| 22610
|-  
|-  
| [[Platinum]]|| 21450
|Platinum]]||align="center"| 21450
|-
|[[Gold]]|| 19300
|-  
|-  
| [[Gold]]|| 19300
|[[Tungsten]]|| 19250
|-  
|-  
| [[Tungsten]]|| 19250
|[[Uranium]]|| 19050
|-  
|-  
| [[Uranium]]|| 19050
|[[Mercury (element)|Mercury]]|| 13580
|-  
|-  
| [[Mercury (element)|Mercury]]|| 13580
|[[Palladium]]|| 12023
|-  
|-  
| [[Palladium]]|| 12023
|[[Lead]]|| 11340
|-  
|-  
| [[Lead]]|| 11340
|Silver]]|| 10490
|-  
|-  
| [[Silver]]|| 10490
|[[Copper]]|| 8960
|-  
|-  
| [[Copper]]|| 8960
|[[Iron]]|| 7870
|-  
|-  
| [[Iron]]|| 7870
|[[Steel]]||7850
|-  
|-  
| [[Steel]]||7850
|[[Tin]]|| 7310
|-  
|-  
| [[Tin]]|| 7310
|[[Titanium]]|| 4507
|-  
|-  
| [[Titanium]]|| 4507
|[[Diamond]]|| 3500
|-  
|-  
| [[Diamond]]|| 3500
|[[Basalt]]|| 3000
|-  
|-  
| [[Basalt]]|| 3000
|[[Granite]]|| 2700
|-  
|-  
| [[Granite]]|| 2700
|[[Aluminium]]|| 2700
|-  
|-  
| [[Aluminium]]|| 2700
|[[Graphite]]|| 2200
|-  
|-  
| [[Graphite]]|| 2200
|[[Magnesium]]|| 1740
|-  
|-  
| [[Magnesium]]|| 1740
|[[Polyvinyl chloride|PVC]]|| 1300
|-  
|-  
| [[Polyvinyl chloride|PVC]]|| 1300
|[[Seawater]] (15°C) &nbsp; &nbsp;|| 1025
|-  
|-  
| [[Seawater]] (15°C)|| 1025
|[[Water]]|| 1000
|-  
|-  
| [[Water]]|| 1000
|[[Ice]] (0°C)|| 917
|-  
|-  
| [[Ice]] (0°C)|| 917
|[[Polyethylene]]|| 910
|-  
|-  
| [[Polyethylene]]|| 910
|[[Ethyl alcohol]]|| 790
|-  
|-  
| [[Ethyl alcohol]]|| 790
|[[Gasoline]]|| 730
|-  
|-  
| [[Gasoline]]|| 730
|Liquid [[Hydrogen]]|| 68
|-  
|-  
| Liquid [[Hydrogen]]|| 68
|[[Aerogel]]|| 3
|-
| [[Aerogel]]|| 3
|-
| any [[gas]]
|    0.0446 times the average [[molecular mass]], hence between [[Hydrogen|0.09]] and ca. [[Tungsten(VI) fluoride|13.1]] (at room temperature and pressure)
|-
| For example [[Earth's atmosphere|air]] (0°), (25°)
|  1.29, 1.17
|}
|}
Aerogel is the world's lightest solid. Also, note the low density of aluminium compared to most other metals. For this reason, aircraft are made of aluminium.


{|
{|
|+align="left"|'''Densities of Air'''
|+align="center"|'''Table 2'''<BR>'''Air Densities at'''<BR>''' Atmospheric Pressure'''
| align="center"|'''Temperature''' &nbsp; <BR>(°C)|| '''Density'''<BR>(kg/m³)  
| align="center"|'''Temperature''' &nbsp; <BR>(°C)|| '''Density'''<BR>(kg/m³)  
|-
|-
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|}
|}


Note the low density of aluminium compared to most other metals. For this reason, aircraft are made of aluminium. Also note that air has a nonzero, albeit small, density. [[Aerogel]] is the world's lightest solid.
The density of any gas (in kg/m<sup>3</sup>), measured at 0 °C and 101.325 kPa, is 0.0446 times the [[molecular mass]] of the gas.


==See also==
==See also==

Revision as of 02:10, 10 June 2008

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Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The density of an object equals its total mass divided by its total volume. An object made of a denser material (such as iron) will have less volume than an equal mass of some less dense substance (such as water). The SI unit of density is the kilogram per cubic metre (kg/cubic m3)

where

ρ is the object's density (measured in kilograms per cubic metre)
m is the object's total mass (measured in kilograms)
V is the object's total volume (measured in cubic metres)

Under specified conditions of temperature and pressure, the density of a fluid is defined as described above. However, the density of a solid material can be defined in several ways. Porous or granular materials have a density of the solid material, as well as a bulk density, which can be variable. For example, if you gently fill a container with sand, and divide the mass of sand by the container volume you get a value termed loose bulk density. If you took this same container and tapped on it repeatedly, allowing the sand to settle and pack together, and then calculate the results, you get a value termed tapped or packed bulk density. Tapped bulk density is always greater than or equal to loose bulk density. In both types of bulk density, some of the volume is taken up by the spaces between the grains of sand. The density of the sand grains, exclusive of the air between the grains, will be higher than the bulk density.

In candy making, density is affected by the melting and cooling processes. Loose granular sugar, like sand, contains a lot of air and is not tightly packed, but when it has melted and starts to boil, the sugar loses its granularity and some entrained air and becomes a fluid. When molded to make a smaller, compacted shape, the syrup tightens up and loses more air. As it cools, it contracts and gains moisture, making the already heavy candy even more dense.

For some materials, density can be calculated based on crystallographic information and molar mass:

where

M is molar mass
N is the number of atoms in a unit cell
L is Loschmidt or Avogadro's number
a, b, c are the lattice parameters

The density with respect to temperature, T, has the following relation:

where

C is the coefficient of cubic expansion.

Experimentally density can be found by measuring the dry weight ( ), the wet weight ( ) and submersed weight ( ), usually in water.


Other units

Density in terms of the SI base units is expressed in kilograms per cubic meter (kg/m3). Other units fully within the SI include grams per cubic centimetre (g/cm3) and megagrams per cubic metre (Mg/m3). Since both the litre and the tonne or metric ton are also acceptable for use with the SI, a wide variety of units such as kilograms per litre (kg/L) are also used. Imperial units or U.S. customary units, the units of density include pounds per cubic foot (lb/ft³), pounds per cubic yard (lb/yd³), pounds per cubic inch (lb/in³), ounces per cubic inch (oz/in³), pounds per gallon (for U.S. or imperial gallons) (lb/gal), pounds per U.S. bushel (lb/bu), in some engineering calculations slugs per cubic foot, and other less common units.

The maximum density of pure water at a pressure of one standard atmosphere is 999.861 kg/m3; this occurs at a temperature of about 3.98 °C (277.13 K).

From 1901 to 1964, a litre was defined as exactly the volume of 1 kg of water at maximum mass, and the maximum density of pure water was 1.000 000 kg/L (now 0.999 972 kg/L). However, while that definition of the litre was in effect, just as it is now, the maximum density of pure water was 0.999 972 kg/dm3. During that period students had to learn the esoteric fact that a cubic centimetre and a millilitre were slightly different volumes, with 1 mL = 1.000 028 cm³. (often stated as 1.000 027 cm³ in earlier literature).

Measurement of Mass

A common device for measuring fluid mass is a pycnometer. A device for measuring absolute mass of a solid is a gas pycnometer.

Density of substances

Perhaps the highest density known is reached in neutron star matter (see neutronium). The singularity at the centre of a black hole, according to general relativity, does not have any volume, so its density is undefined.

The densest naturally occurring substance on Earth is iridium, at about 22 650 kg/m3.

Table 1
Densities of
Various Substances
Substance Density
(kg/m³)
Iridium 22650
Osmium 22610
Platinum]] 21450
Gold 19300
Tungsten 19250
Uranium 19050
Mercury 13580
Palladium 12023
Lead 11340
Silver]] 10490
Copper 8960
Iron 7870
Steel 7850
Tin 7310
Titanium 4507
Diamond 3500
Basalt 3000
Granite 2700
Aluminium 2700
Graphite 2200
Magnesium 1740
PVC 1300
Seawater (15°C)     1025
Water 1000
Ice (0°C) 917
Polyethylene 910
Ethyl alcohol 790
Gasoline 730
Liquid Hydrogen 68
Aerogel 3

Aerogel is the world's lightest solid. Also, note the low density of aluminium compared to most other metals. For this reason, aircraft are made of aluminium.

Table 2
Air Densities at
Atmospheric Pressure
Temperature  
(°C)
Density
(kg/m³)
- 10 1.341
- 5 1.316
0 1.293
+ 5 1.269
+ 10 1.247
+ 15 1.225
+ 20 1.204
+ 25 1.184
+ 30 1.164

The density of any gas (in kg/m3), measured at 0 °C and 101.325 kPa, is 0.0446 times the molecular mass of the gas.

See also