Properties of hydrogen peroxide

Hydrogen peroxide was discovered by L.Y. Thenard in 1818. It occurs in nature in rain, snow, dew, air. Pure hydrogen peroxide is a viscous liquid: it is colourless, when viewed in thin layers but appears bluish in thick layers. The liquid has no odour.

Dilute aqueous solution has a peculiar metallic lustre. If concentrated sulfuric acid is mixed with hydrogen peroxide at low temperature, oxygen rich in ozone will be evolved.

The liquid decomposes rapidly when heated at ordinary atmospheric pressure, but under reduced pressure it can readily distilled. It boils at 68-69 °C under pressure of about 26 mm. The liquid crystallizes in needle-like prisms at –2 °C. It is soluble in water in all proportions.

Pure hydrogen peroxide is fairly stable. Dilute aqueous solutions are kept well. A 3 % solution showed no appreciable change when kept a year. Alkali solutions are not kept well. If alcohol or ether is added, the aqueous solutions will become more stable. Pure H₂O₂ is decomposed very rapidly if any dust is present.

Like ozone hydrogen peroxide possesses strong oxidizing properties. It can act as an oxidizing as well as reducing agent. Dilute aqueous solutions of hydrogen peroxide are used for bleaching (silk, feathers, straw, hair, ivory, teeth). It can be used in medicine as an antiseptic. Hydrogen peroxide is employed in analytical work for the oxidation of sulfites to sulfates, ferrous to ferric salts, nitrites to nitrates, etc.

3. Make up the plan to the text.

4. Give a brief summary of the text.

Text D

1. Read the text and choose the most suitable title out of the given ones:

a) An abundant element.

b) Sodium.

c) A very reactive element.

Sodium in the form of compound is widely distributed and abundant element but on account of its intense chemical activity it is never found free.

Sodium is a silvery-white, lustrous metal which tarnishes at once when exposed to the air owing to the formation of a film of oxide. On account of the ease with which it is oxidized, it must be kept immersed in a liquid containing no oxygen. It is lighter than water (sp. gr. 0.93); it is soft, so that it can be cut with knife, and at ordinary temperature it can be moulded between the fingers. Sodium melts at 97.5 °C and boils at 880 °C.

The vapour, which is purple when seen in thick layers, has a density of 12.85 (H₂₌₁) indicating that it is probably almost entirely monatomic.

Sodium is a good conductor of electricity. Chemically sodium is. It combines vigorously with oxygen, burning readily in air with brilliant, yellow flame, and forming a mixture of the oxide and peroxide. It combines directly with the halogens and with phosphorus taking fire when heated with these elements. It also combines with hydrogen when heated. The vigour of its combination with oxygen is such that sodium will react with most oxides liberating the element previously combined with the oxygen. Thus, it acts energetically with water, forming sodium hydroxide and hydrogen and the heat of the reaction is sufficient to melt the sodium which swims, as a globule on the surface of the water. The heat evolved is, however, not great enough to ignite the hydrogen unless large pieces of sodium will dissolve in liquid ammonia forming a blue solution.

2. Write out:

а) key words and terms;

b) the sentences expressing the main idea of each paragraph.

Unit 4

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