Two genral method of sepration
Answers
The phrase ‘like oil and water’ refers to things that do not mix, just like, well – oil and water, whose chemical properties prevent their mixing. But in many cases, what we really need are ways to achieve the opposite – separate mixed substances.
Crude oil is a good example: It is a mixture of numerous carbohydrates (compounds that consist of hydrogen and carbon), some of which are used to power engines as fuel, and others in the manufacturing of plastics or other compounds. A distillation process separates between them. Alongside distillation, there is a range of separation techniques – some physical, others chemical. The former are based on the physical properties of materials, i.e., properties that can be observed or measured without changing the identity of the material (for example, its state of matter), while chemical methods are based on chemical properties – which determine substance identity.
Physical separation methods
Physical separation methods, such as filtration and distillation, are based on the difference in particle size and on the boiling point of the substances in the mixture, respectively. These are properties that can be observed and measured without changing the material itself.
Filtration
This is the simplest separation method, which can be conducted using basic household equipment. In daily life, it is applied in the separation of solids from the liquids in which they were cooked – pasta, for example.
Filtration is based on the fact that the smaller water particles can easily pass through the filter, which retains the larger solid particles. When straining pasta, our interest lies in the solids, but in other cases, it is the liquid that we seek, so we need to remove the larger solids, keeping those in the filter. The filter hole size determines which materials are retained in the filter and which pass through it.
Sterilization is an example of an industrial application of filtration. To remove a bacterial contamination from a solution, the solution is passed through a filter. The microorganisms are trapped in the filter, while the smaller solution molecules pass through. Also called microfiltration (because of the relatively small size of the molecules), this process is used for sterilization when other techniques, such as heating or ultra-violet radiation, are inapplicable due to their potential harmful effects on the solution’s molecules.
To filter out even smaller molecules, which do not exceed 100 nanometers in size (less than one thousandth of a millimeter), a process known as nanofiltration is used. The main feature of this process is not pore size but the electrical forces at work between the molecules, whose significance increases as the size of the molecule decreases. An example of nanofiltration is reverse osmosis, used for desalination. In reverse osmosis, a selective membrane, which allows water to pass through it but not the dissolved particles, is used. Pressure is applied to reverse the natural flow of the water, forcing them to move from the more concentrated solution to the weaker. Thus, salts and contaminants are concentrated on one side and clean water – on the other.
Distillation
In distillation, components of a liquid mixture are separated on the basis of the differences in their boiling temperatures. In its simplest form, distillation involves boiling the mixture and collecting the vapor in a condensation vessel, where it turns back into a liquid. The first vapors to appear are those of the substance whose boiling point is the lowest. As the boiling continues, the vapors of the next substance are captured in a different condensation vessel, and so on.
To find out when one component finished boiling and another began, the mixture’s temperature must be constantly monitored. During the boiling of one substance, the mixture’s temperature will be ‘stuck’ at that material’s boiling point, and then will continue to rapidly increase.
Crude oil distillation is based on this principle, which constitutes the first step of separation, whereby oil is separated into fractions – groups of substances with different boiling temperature ranges. Then chemicals are added, with the purpose of improving the quality of the distillates.
The primary fractions produced by the initial distillation of crude oil are naphtha, used to create benzene for car engines and as a raw material for the plastic industry; kerosene, which is used to create fuel for jet engines; diesel fuel used to power diesel engines, and mazut, used as power station fuel.
Answer:
Mixtures can be separated using a variety of techniques. Chromatography involves solvent separation on a solid medium. Distillation takes advantage of differences in boiling points. Evaporation removes a liquid from a solution to leave a solid material.
Explanation:
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