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Academia - Collins - Pocket Scientific Dictionaries - Chemistry - English - French - Arabic Letter 1_ O


octane rating
index m d'octane

Actin grade. The mixture of petrol and air must explode at exactly the right moment in an internal combustion engine. If the wrong type of fuel is used, the mixture may ignite prematurely, leading to the well-known “knocking” sound in the engine.

The octane grade (or octane number) of gasoline is a measure of the anti-knock qualities of gasoline. The higher the score, the better. Four-star gasoline has an octane rating of 98. The higher the proportion of branched hydrocarbon molecules in the fuel, the higher the octane rating.

The grades of octane can be raised by adding materials such as tetraethyl lead. Unfortunately, this substance leads to air pollution.


oil
huile f. petroleum m

Liquid fat oil, such as butter, olive oil, sunflower oil, etc. The same word is sometimes used in place of the word petroleum.


oleum
oléum m

the first day. A solution of sulfur VI (sulfur oxide) in concentrated sulfuric acid. It is a very abrasive material and a strong oxidizing agent. See contact process.


ore
minerai m

metal. A naturally occurring substance from which an element can be extracted, such as:

Galena: lead, hematite iron, calomine: zinc.


organic chemistry
chimie f organique

organic chemistry . Study of carbon compounds, and does not include carbonates, carbon dioxide, etc.
See inorganic chemistry.


oxidation
oxidation f

oxidation. A substance is oxidized if:

I gained oxygen
2MgO + O2 → 2MgO

Lost hydrogen
CH4 + Cl2 → CH3CI + HCI

Electrons lost
Cu → Cu2+ + 2e

See redox, reducing and oxidizing agent


oxide
oxyde m

oxide. A compound composed of only an element and oxygen. Oxides can be formed by:

(a) Direct combustion of elements.
(b) Oxidized compounds.
(c) The action of heat on carbonates, hydroxides, or some nitrates.

Examples:

2Mg(solid) + O2(gas) → 2MgO(solid)

CH4 + 202 → CO2 + 2H₂O
(gas) (gas) (gas) (gas)

CuCO3 (solid) → CuO (solid) + CO2 (gas)

Pb(OH)2 (solid) → PbO (solid) + H2O (gas)

2Zn(NO3)2 → 2ZnO + 4NO2 + O2 (solid) (gas) (solid) (gas))

The oxides can be returned to the element by a suitable reducing agent such as hydrogen, carbon or carbon monoxide. See basic oxide, acidic oxide, and amphoteric oxide.


oxidizing agent
agent m oxydant

oxidizing agent. Something that causes the oxidation of another substance.
When this happens, the oxidation agent returns.

Common oxidizing agents:

Oxygen O2
Chlorine Cl2
Ozone O3
Hydrogen peroxide H2O2
Potassium (VII) manganate KMnO4

Oxidizing agents in action:

2Mg(solid) + O2(gas) → 2MgO(solid)

Cl2 (gas) + 2Na (solid) → 2NaCI (solid)

H2O2 + H2S → 2H2O + S
(solid) (liquid) (garlic) (aqueous)