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Firstly, a pure chemical should appear in at least one chemical phase and can also be characterized by its phase diagram. Secondly, a pure chemical should prove to be homogeneous (i.e., a uniform substance that has the same composition throughout the material [2]). The perfect pure chemical will pass all attempts to separate and purify it further.
Plumbago – a mineral, graphite; not discovered in pure form until 1564; Powder of Algaroth – antimony oxychloride, formed by precipitation when a solution of butter of antimony and spirit of salt is poured into water. Purple of Cassius – formed by precipitating a mixture of gold, stannous and stannic chlorides, with alkali. Used for glass ...
In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons. Nuclear scientists, however, define a pure element as one that consists of only one isotope. [18] For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each.
A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. [1] [2] Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combined without reacting, they may form a chemical mixture. [3]
The name mustard gas is technically incorrect; the substances, when dispersed, are often not gases but a fine mist of liquid droplets that can be readily absorbed through the skin and by inhalation. [3] The skin can be affected by contact with either the liquid or vapor.
GCSE Bitesize was launched in January 1998, covering seven subjects. For each subject, a one- or two-hour long TV programme would be broadcast overnight in the BBC Learning Zone block, and supporting material was available in books and on the BBC website. At the time, only around 9% of UK households had access to the internet at home.
[64] [65] In 1811 Louis-Joseph Gay-Lussac and Louis-Jacques Thénard probably prepared impure silicon, [66] and Berzelius obtained the pure element in 1823. [67] The name was proposed to be changed to silicon by Thomas Thomson in 1817, and this was eventually accepted because of its analogies to boron and carbon. 13 Aluminium: 1746 J. H. Pott 1824
If a substance can exist but is not thermodynamically stable (for example, a supercooled liquid), it is called a metastable state. A non - physical standard state is one whose properties are obtained by extrapolation from a physical state (for example, a solid superheated above the normal melting point, or an ideal gas at a condition where the ...