Практикалық сабақтарының тақырыптары мен мазмұны Practical assignment №1
жүктеу/скачать 64,23 Kb.
|
chemistry (1)
- Бұл бет үшін навигация:
- PRECIPITATION
- ELECTROLYSIS
| Notes to the text
1. the problem at hand - рассматриваемая проблема 2. are more complex than - более сложны чем EXTRACTION Liquid-liquid phase separations are possible when a metal forms a compound soluble in two immiscible liquids. The distribution of the compound between the two liquids can be considered to be a solubility contest. Practical considerations dictate that one of the liquids must be water. Among the liquids other contestants are: carbon tetrachloride, chloroform, carbon disulfide, ethers, paraffin hydrocarbons, and aromatic hydrocarbons. Alcohols cannot be added to this list. Most inorganic compounds just are not interested in the organic solvents which are immiscible with water. Sometimes, however, a complexing agent can be found which will coach an inorganic substance into an organic solution. Cupric, lead, zinc, silver, mercuric, and cadmium salts, for example, will dissolve, in either chloroform or carbon tetrachloride if it contains some dithizone. PRECIPITATION The most generally useful technique for accomplishing a phase separation is the solid-liquid separation, obtained in a precipitation. To have wide applicability a precipitant should form compounds with many metal ions, and these compounds should have a wide range of solubility. To obtain proper conditions, the concentration of the precipitant should be controlled easilly. What sort of precipitant is most desirable depends upon many variables: how many samples must be determined, what constituents are present, what reagents are at hand, what time is available, what accuracy is desired, etc. ELECTROLYSIS Another type of solid-liquid phase separation is furnished by electrolytic techniques. Two electrodes are placed in the solution of interest, and a current is passed through the solution at a voltage sufficient to reduce some but not all of the metals present. If the current and concentrations are adjusted properly, the metals which are reduced will plate out on the electrode in a pure metallic deposit which can be dried and weighed directly. жүктеу/скачать 64,23 Kb. Достарыңызбен бөлісу:
|