مصادر الكيمياء موقع لتعليم الكيمياء بصورة مبسطة

adsorption indicator (absorption indicator) A type of indicator used in reactions that involve precipita­tion. The yellow dye fluorescein is a common example, used for the reac­tion NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq) As silver nitrate solution is added to the sodium chloride, silver chlo­ride precipitates. As long as Cl” ions are in excess, they adsorb on the precipitate particles. …

A technique for cooling a paramagnetic salt, such as potassium chrome alum, to a temperature near absolute zero. The salt is placed between the poles of an electromagnet and the heat produced during magnetization is re­moved by liquid helium. The salt is then isolated thermally from the sur­roundings and the field is switched off; the salt is demagnetized adiabati­cally and …

adiabatic approximation An ap­proximation used in quantum me­chanics when the time dependence of parameters, such as the internuclear distance between atoms in a molecule, is slowly varying. This ap­proximation means that the solution of the Schrodinger equation at one time goes continuously over to the solution at a later time. It was formu­lated by Max Born and the Soviet physicist …

A substance added to another substance or material to improve its properties in some way. Additives are often present in small amounts and are used for a variety of purposes, as in preventing corrosion, stabilizing polymers, and preserving and improving foods.

A dark brown powder, a hydrated form of platinum (IV) oxide (PtO2), produced by heating chloroplatinic acid (H2PtC16) with sodium nitrate (NaNO3). Platinum ni­trate is produced, and this decom­poses to Platinum (IV) oxide with evolution of NO2 and oxygen. It is used in hydrogenations of alkenes to alkanes, nitro compounds to aminos, and ketones to alcohols. The actual catalyst is …

A colourless crys­talline hydrocarbon C10H16; m.p. 269°C. It is found in certain petro­leum fractions. The structure con­tains three symmetrically fused cyclohexane rings.

The process of introducing an acyl group (RCO-) into a compound. The usual method is to react an alcohol with an acyl halide or a carboxylic acid anhydride; e.g. RCOCl + R’OH → RCOOR’ + HCl

An analytical technique that can be used to detect most elements when present in a sample in milligram quantities (or less). In neutron activation analysis the sample is exposed to a flux of thermal neutrons in a nuclear reac­tor. Some of these neutrons are cap­tured by nuclides in the sample to form nuclides of the same atomic number but a …

تقطير أيزوتروبي azeotropic distillation  : تقنية لفصل مكونات الأزيوتروب من خلال إضافة سائل ثالث لتكوين أزيوتروب جديد مع أحد من المكونات الأصلية، و تستخدم عملية التقطير هذه على نطاق شائع لفصل الإيثانول عن الماء من خلال إضافة البنزين حيث يتحد مع الماء .   بوسترات (لوحات) كيميائية بدقة عالية (أكثر من 25 لوحة) من تصميم الأستاذ أكرم أمير العلي   تطبيقات …

الترسيم الإشعاعي الذاتي autoradiography : تقنية مخبرية يتم فيها وضع عينة مشعة بالاتصال مع أو بالقرب من طبقة فوتوغرافية بحيث يتم الحصول على سجل لانتشار النشاط الإشعاعي في العينة. فالفيلم يتم تسويده من خلال الإشعاعات المتأينة الصادرة عن الأجزاء المشعة في العينة. و لتقنية الترسيم الإشعاعي الذاتي عددا من التطبيقات و خصوصا في دراسة الخلايا و الأنسجة الحية.