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Physical and chemical properties and applications of mercury

Among all metals, mercury has the lowest melting point and boiling point, so mercury is a very easy-to-evaporate substance. At room temperature, the mercury vapor pressure is very low, which is conducive to the room temperature start of mercury-containing discharge lamps; at high temperatures, the mercury vapor pressure is very high, which is conducive to the buffering effect of mercury vapor as a buffer gas in discharge lamps. Therefore, in some discharge lamps, mercury has a role that other elements cannot replace.

The first excitation potential of mercury is 4.86V, and the ionization potential is 10.42V, which is lower than that of inert gases and ordinary gases, and it is easy to conduct electricity. Therefore, it is often used as a discharge luminous substance in discharge lamps.

In terms of chemical properties, mercury is a less active element, which is relatively stable at room temperature and only slightly oxidized. Mercury is oxidized by air only when the temperature is close to the boiling point. Mercury has a weak interaction with gases H, CO, 002 and N₂. Mercury can be well dissolved in nitric acid and aqua regia, and also reacts with concentrated hydrochloric acid and concentrated sulfuric acid.

The reaction formula is:

Hg +2H₂SO→HgSO+ 2H₂0 + SO₂↑

But mercury does not work with dilute hydrochloric acid, sulfuric acid and alkali. Mercury and sulfur can directly combine:

Hg+S→→HgS

Using this property, when mercury is lost on the ground in tiny particles, a layer of sulfur powder can be sprinkled on it to remove it. Mercury reacts with halogens. The main compounds are calomel, also known as mercurous chloride (Hg:O1:), which is a white crystal or powder that is difficult to dissolve in water; mercuric chloride, also known as mercuric chloride (HgCls), is a colorless crystal or white crystalline powder that is often in water, which is highly corrosive and highly toxic!

Many metals can be dissolved in mercury to form amalgams. Alkali metals, alkaline earth metals, magnesium, aluminum, zinc, tin, lead, cadmium, silver and gold are particularly easy to form amalgams. Titanium amalgam, indium amalgam and sodium amalgam are widely used in electric light sources.

Copper, nickel and platinum have very low solubility in mercury; tungsten, iron and molybdenum are insoluble in mercury, and non-metallic materials such as graphite, glass, ceramics and mica do not react with mercury.

Pure mercury does not wet glass at all, but when it contains a small amount of impurities, it begins to adhere to the glass surface. Therefore, the surface condition of mercury can be used as the most sensitive indicator of mercury purity. If the newly filtered mercury has a very bright luster, the impurities contained in it generally do not exceed 0.0001%.

Mercury has a very uniform volume expansion coefficient between 0 and 200°C and does not wet glass, so it is often used to fill thermometers. Because mercury has a high density and low vapor pressure, it is often used to make mercury pressure gauges in vacuum systems.

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