Separation Techniques Flashcards
Methods that separate solid from solid:
Sublimation, Magnetic attraction
Methods that separate solid from liquid:
Filtration, Decanting, Crystallisation, Evaporation to dryness
Methods that separate liquid from liquid:
Simple distillation, Fractional distillation, Paper chromatography, Separating funnel
Methods that only separate substances:
Magnetic attraction, Sublimation, Separating funnel, Filtration, Evaporation until dryness, Decanting
Methods that separate and purify substances:
Crystallisation, Simple distillation, Fractional distillation
Methods that separate and identify substances:
Paper chromatography, simple distillation, fractional distillation
Describe sublimation.
A process that separates a mixture of solids, in which one of the solids sublimes and undergoes a change in state from solid to gas upon heating.
State the process of a gas turning into solid state.
Deposition
1: State a subliming substance that melts at atmospheric temperature.
2: State a subliming substance that does not melt at atmospheric temperature.
- iodine, naphthalene
2: carbon dioxide
Describe the process of crystallisation fully.
A solid is dissolved in a liquid to form a solution. Filtration is performed to remove excess solute from the solution. Heat the solution until most of the solvent has evaporated. The solution is then allowed to cool, forming a saturated solution. The solution is no longer able to hold any more solute and thus the dissolved solid appear as crystals, while the impurities remain dissolved in the solution.
Why is it necessary to cool the solution?
To decrease the solubility of the solute and thus form crystals.
What is the recommended procedure after crystallisation (i.e. after the crystals appear)?
Perform filtration again and obtain the residue which are the crystals. Next, wash the crystals with a bit of cold deionised water before drying them on a filter paper.
Describe the process of evaporation until dryness.
A solid is dissolved in a liquid to form a solution. Filtration is performed to remove excess solute from the solution. The solution is then heated until all the solvent has evaporated. The solution is no longer able to hold any more solute and thus the dissolved solid appear as crystals.
State 2 disadvantages of evaporation until dryness compared to crystallisation.
1) It may decompose thermally unstable substances such as sugar.
2) When the solvent evaporates, the impurities may remain with the solid.
In filtration, name the scientific terms of
1. the solid collected in the filter paper;
2. the liquid/solution passing through the filter paper
- residue
- filtrate
State two disadvantages of filtration.
1) The solids collected on the filter paper may be contaminated with some fluid and thus they have to be washed thoroughly.
2) The filtrate may contain fine particles if the pore size of the filter paper is not small enough to prevent the particles from flowing through.
Describe the process of decanting.
Decanting separates an insoluble solid from a liquid by pouring the liquid from the container.
Name and describe the product from distillation.
The product is known as the distillate and it is pure.
State the function of simple distillation.
To obtain a pure solvent from a solution of a solute.
Describe the process of simple distillation.
The mixture is heated and the liquid in the mixture boils and turn into pure vapour. This pure vapour rises and enters the condenser, before it touches the cool surface and cooled to its liquid state. This liquid, also known as the distillate, is collected.
State the physical processes involved in distillation.
Boiling, Condensation
Why should the bulb of the thermometer be placed at the entrance to the condenser?
To measure only the vapour that is distilling and not any other vapours inside the mixture.
Why should cold water flow in from the bottom of the condenser?
To ensure that the column in the condenser is fully filled with water so as to ensure efficient cooling of the hot vapours to liquid.
Explain why a stopper is essential for fractional distillation to take place.
To prevent vapours/gases from escaping.
