أكاديميا - كولنز - معاجم الجيب العلمية - الكيمياء - انكليزي - فرنسي - عربي الحرف ٥_ h

Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 5_ H


hydrogen sulphide ( H2S )
sulfur m d'hydrogen

Hydrogen sulfide . A colorless gas with a nauseating smell that resembles the smell of rotten eggs. It results from the rotting of organic matter containing sulfur, which is often found accompanying oil. In the laboratory, it is produced by the action of acid in metallic sulfide, such as:

FeS + 2HCI → FeCl2 + H2S
(Gas) (Aqueous) (Aqueous) (Solid)

This gas is highly toxic. It, like hydrogen cyanide (HCN), prevents the transfer of energy within the body. Its presence can be detected as it turns a blotting paper dipped in lead (II) salt black, due to the formation of insoluble lead (II) sulfide:

Pb2+ + H2S PbS + 2H+

A solution of hydrogen sulfide in water forms a weak acid, while the gas is a reducing agent.

hydrolysis
hydroiyse f

Water analysis. This term refers to the decomposition of a substance by water. Water also dissociates and esters are hydrolyzed.


hydrophilic
hydrophile

Water friendly. This term means “water-loving,” and is used to describe sections of molecules that dissolve immediately in water. For example, the anion end of a detergent molecule is hydrophilic. This “gravity” of water is what makes the detergent work. The other end of the molecule is hydrophobic, meaning “water-hating.”

The part of the molecule that repels water is neither dissolved in water nor attracted to it. In the detergent, this end of the molecule is attached to the fat or oils present in the substance being cleaned. See soap and detergent.


hydrophobic
hydrophobe

Water repellent. See hydrophilic.


hydroxide ion (OH¯)
ion m hydroxyde

Hydroxide ion. This ion is found in all alkalis, such as sodium hydroxide, and in alkaline solutions. It is present in all aqueous solutions due to the dissociation of water:
H2O = H+ + OH-

Solutions in which hydroxide ions exceed hydrogen ions are described as alkaline and have a pH greater than .7. The hydroxides of the group are | Soluble in water. Some other hydroxides are less soluble, such as Mg(OH) and 2(Ca(OH). Insoluble hydroxides can be precipitated using soluble hydroxide:

Pb (NO3)2 + 2NaOH → Pb (OH)2 + 2NaNO3
(Aqueous) (Solid) (Aqueous) (Aqueous)


hygroscopic
hygroscopique

Humidity. A hygroscopic material can absorb up to 70 percent of its mass of water without dissolving or getting wet. Examples include: copper oxide (11), sodium chloride, and silica gel. See deliquescence.