Seperation techniques (C8)

Question 1

what is electrolysis?

Answer 1

the breakdown of an ionic compounds using electricity

Question 2

for electrolysis to occur the ions must be?

Answer 2

mobile

Question 3

how can the ions be mobile?

Answer 3

dissolving the ionic compound in water or by melting it

Question 4

what is an electrolyte?

Answer 4

mixture containing mobile ions

Question 5

what occurs in electrolysis?

Answer 5

• a direct current is applied through the electrolytes using two electrodes
  -positive ions are attracted to the negative electrode (cathode) and negative ions are attracted to the positive electrode (anode).
  -reduction occurs at the cathode and oxidation occurs at the anode

Question 6

electrodes in electrolysis must be?

Answer 6

unreactive such as platinum

Question 7

what is decanting?

Answer 7

pouring out liquid or solution away without disturbing the solid

Question 8

what occurs in filtration?

Answer 8

separation of a liquid (or solution) from an insoluble solid. The solid particles are larger and trapped in the mesh of filter paper.

Question 9

when and how do you used a separating funnel?

Answer 9

used to separate two immiscible liquids. There are two layers and the upper layer has a lower density. When the tap is opened, the lower layer can be poured out.

Question 10

what is distillation?

Answer 10

used to separate two substances with differing boiling points. Simple distillation is typically used to separate the solvent from the solution leaving the solute behind.

Question 11

what occurs in distillation?

Answer 11

-mixture is heated above boiling point of solvent
-solvent becomes vapour and starts to spread out through apparatus.
-in the condenser, the vapour cools and condenses. Droplets run to collection vessel.
-The higher boiling point solute remains in the heated flask

Question 12

how is the condenser remained cool?

Answer 12

Cold water is passed through the condenser in an outer jacket. It is always added at the bottom to ensure that there is always cold water in the jacket and that condensation occurs all the way along the condenser.

Question 13

what is fractional distillation?

Answer 13

used to separate miscible liquids (ones soluble in each other) from a mixture. In the separation of larger mixtures such as the hydrocarbons in crude oil, the separation can be into groups of compounds with similar boiling points or it can be used to separate individual components.

Question 14

what occurs in fractional distillation?

Answer 14

-mixture heated
-When the temperature of the mixture reaches the boiling point of the component with the lowest boiling point, the temperature no longer rises and the first component boils. This lowest boiling point component rises up the fractionating column towards the condenser where it is condensed and collected. The thermometer at the entrance to the condenser monitors the boiling point of the component being distilled.
-Once the first component has boiled away, the remaining mixture then rises in temperature

Question 15

what is evaporation and crystallisation?

Answer 15

technique used to separate solvent from solute and uses the difference in boiling point and/or volatility to separate the mixture.

Question 16

how does crystallisation occur?

Answer 16

solution is heated gently until crystals just begin to appear. The remaining concentrated solution is then left to evaporate.

Question 17

what will happen if you heat the remaining concentrated solution in crystallisation?

Answer 17

solids may decompose

Question 18

what is chromatography?

Answer 18

used to separate mixtures of different solutes/ liquids

Question 19

separation of substances in chromatography is dependent on?

Answer 19

relative affinity

Question 20

what is the mobile phase in chromatography?

Answer 20

solvent

Question 21

how does chromatography occur?

Answer 21

-small sample of mixture is spotted on chromatography paper on pencil base line
-this is placed in beaker with solvent below pencil line and lid is placed
-the solvent rises by capillary action and shouldn’t reach the top of paper

Question 22

If the component adsorbs more strongly to the paper (the stationary phase)?

Answer 22

then it does not travel up as readily

Question 23

Rf value (retention value) is calculated by?

Answer 23

distance travelled by sample/ distance travelled by solvent

Question 24

what is centrifugation?

Answer 24

used to separate heterogeneous mixtures based on their differences in particle mass.

Question 25

how does centrifugation occur?

Answer 25

encourages settling by spinning the mixture at high speed in a horizontal circle. As the mixture is spun, the heavier particles are brought to the end of the tube. The heaviest particles settle out first, becoming a pellet at the bottom of the tube. The remainder, called the supernatant may be decanted into a new tube and spun again at a higher speed to separate the smaller particles.