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This programme examines what is meant in chemistry by solubility. This examination leads to the concept of solubility product. A table of solubility products is then used to explain the rational be...hind the selection of additives used in the purification of brine by precipitation. In industry chlorine is produced by the electrolysis of brine produced from rock salt. The sodium chloride brine contains many of the impurities that occurred in the seas from which the rock salt was formed. The main impurities that must be removed before electrolysis are named. With this practical problem in mind the programme turns to a more theoretical consideration of how ions behave in solution. Experiments show that when ionic solutions are mixed anions and cations may combine to form a solid precipitate. Experiments are then performed mixing table salt with water. These show a) that even a compound which is normally considered soluble has a definite limit to its solubility. b) that the saturated solution has a fixed concentration at a particular temperature. One conclusion of this experiment is that if solid is added to its saturated solution it will not dissolve. An experiment using radioactively labelled solid shows that solid does still dissolve. This apparent dilemma is explained by the concept of dynamic equilibrium. The meaning of the term solubility product is then established, Solubility products are then used to explain why in industry sodium hydroxide is used to precipitate calcium ions, and sodium carbonate to precipitate magnesium ions.
This programme examines what is meant in chemistry by solubility. This examination leads to the concept of solubility product. A table of solubility products is then used to explain the rational be...hind the selection of additives used in the purification of brine by precipitation. In industry chlorine is produced by the electrolysis of brine produced from rock salt. The sodium chloride brine contains many of the impurities that occurred in the seas from which the rock salt was formed. The main impurities that must be removed before electrolysis are named. With this practical problem in mind the programme turns to a more theoretical consideration of how ions behave in solution. Experiments show that when ionic solutions are mixed anions and cations may combine to form a solid precipitate. Experiments are then performed mixing table salt with water. These show a) that even a compound which is normally considered soluble has a definite limit to its solubility. b) that the saturated solution has a fixed concentration at a particular temperature. One conclusion of this experiment is that if solid is added to its saturated solution it will not dissolve. An experiment using radioactively labelled solid shows that solid does still dissolve. This apparent dilemma is explained by the concept of dynamic equilibrium. The meaning of the term solubility product is then established, Solubility products are then used to explain why in industry sodium hydroxide is used to precipitate calcium ions, and sodium carbonate to precipitate magnesium ions.
| Module code and title: | ST294, Principles of chemical processes |
|---|---|
| Item code: | ST294; 02 |
| First transmission date: | 24-02-1975 |
| Published: | 1975 |
| Rights Statement: | |
| Restrictions on use: | |
| Duration: | 00:23:41 |
| + Show more... | |
| Producer: | Barrie Whatley |
| Contributors: | Stuart Bennett; Ian Boustead; George Loveday |
| Publisher: | BBC Open University |
| Keyword(s): | Additives; Anions; Brine; Cations; Chlorine; Electrolysis; Ions; Purification; Rock salt; Table of solubility |
| Master spool number: | 6HT/71424 |
| Production number: | 00525_1154 |
| Videofinder number: | 747 |
| Available to public: | no |
