Simple distillation, liquid/solid solutions

N4H4 is made by simple metathetic reaction in liquid, solid, or gaseous media which may involve distillation or precipitation. For example, equimolar amounts of ammonium chloride and sodium azide may be distilled with an equal quantity of water. At 160°C pot temperature, the product volatilizes with water vapors and solidifies in the condenser tube which should, therefore, be at least 1 inch wide [305]. Equally clean and safe is a gas-phase reaction which requires, however, the preparation of hydrazoic acid gas. The reaction takes place in a long, 1-inch-wide glass tube which has two inlet tubes with orifices 20 inches apart, and a vent. The HN3 gas, carried with nitrogen, and excess ammonia stream in and precipitate the product as fine needles [39]. N4H4 is also precipitated when ammonia gas is bubbled into an ethereal hydrazoic acid solution [86]. The product stays in solution when HN3 vapors, carried with nitrogen, are bubbled into aqueous ammonia [306]. 

Diazotization, Isoiation, and Purification Add 0.07 g of powdered sodium nitrite in small portions to the vial. When the addition is complete, use a drop or two of absolute ethanol to rinse any solid that may stick to the sides of the vial into the solution. Equip the vial with a condenser and heat the mixture under gentle reflux for about 10 min. Add 2 mL of hot water to the vial and equip it for simple distillation. Steam-distill the mixture until about 1 mL of liquid remains in the vial. 

In this section, we will consider only solutions in which the liquid component has the majority mole fraction (the solvent) and the solid component has the minority mole fraction (the solute). We will also assume that the solid solute is non-ionic, because the presence of oppositely charged ions in solution affects the properties of the solution (which will be considered in the next chapter). There is also a consideration that is implicit in specifying a solid component It contributes nothing to the vapor phase that is in equilibrium with the solution. One way of speaking of this is to state that the solid is a nonvolatile component. Solutions of this sort are therefore easy to separate by simple distillation of the only volatile component, the solvent, rather than the more complicated fractional distillation. Figure 7.20 shows two experimental setups for simple distillation. Compare these to Figure 7.9. 

A simple apparatus for steam distillation is shown in Fig. 2.102. Flask A contains the liquid to be steam distilled it is fitted with the splash-head B which prevents the carry-over of the contents of the flask A into the receiver. To carry out a steam distillation, the solution (or mixture of the solid with a little water) is placed in the flask A, and the apparatus is completely assembled. Steam is passed into flask A, which is itself heated by means of a flame to prevent too rapid an accumulation of water. If the substance crystallises in the condenser and tends to choke it, the water should be run out of the condenser for a few minutes until the solid material has been melted and carried by the steam into the receiver the water should then be cautiously readmitted to the hot condenser. It is best to use a condenser of the double surface type if the rate at which the steam distillation is carried out is rapid if necessary two such condensers connected in series may be used since in most steam distillations best results are obtained when the process of distillation is carried out rapidly. The passage of steam is continued until no appreciable amount of water-insoluble material is... 

If dry liquid ammonia is needed this is usually obtained by distillation ff sodium. The appropriate volume of ammonia is condensed as above 2nd small pieces of sodium are added to produce a blue solution. The ammonia can then be distilled using a normal distillation apparatus (Chapter 11) except that the receiver (usually the reaction flask) is cooled in a solid bon dioxide/acetone cooling bath. The ammonia in the distillation flask must remain blue throughout). The distillation apparatus is disconnected Srom the receiver which is then fitted with a cold-finger condenser and the reaction carried out as normal. The work up is usually simple. Solid ammonium chloride is added carefully and the ammonia allowed to evaporate (Chapter 10). The product may then be isolated and purified in the usual way. 

Suppose that we scooped up some sand with our sample of seawater. This sample is a heterogeneous mixture, because it contains an undissolved solid as well as the saltwater solution. We can separate out the sand by simple fiitration. We pour the mixture onto a mesh, such as a filter paper, which allows the liquid to pass through and leaves the solid behind (see Figure 2.17). The salt can then be separated from the water by distillation. The total separation process is represented in Figure 2.18. All the changes involved are physical changes. 

Wastewater can be treated by several physical processes. In some cases, simple density separation and sedimentation can be used to remove water-immiscible liquids and solids. Filtration is frequently required, and flotation by gas bubbles generated on particle surfaces may be useful. Wastewater solutes can be concentrated by evaporation, distillation, and membrane processes, including reverse osmosis, hyperfiltration, and ultrafiltration. Organic constituents can be removed by solvent extraction, air stripping, or steam stripping. 

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