Separating Techniques - 3rd

Question 1

what are the separating techniques?

Answer 1

• filtration
• crystallisation
• making pure salt from rock salt
• simple distillation
• fractional distillation
• paper chromatography

Question 2

describe filtration?

Answer 2

filtration can be used to separate a solid from a liquid.
separating techniques: picture 1
for example, sand can be separated from water by filtration.
The substance left in the paper is called the residue and the liquid which comes through is called the filtrate.
filtration can also be used to separate two solids from each other if only one of them is soluble in water.

Question 3

describe crystallisation?

Answer 3

• used to separate a solute from a solution
• e.g. to separate sodium chloride from a sodium chloride solution
• solution is heated in an evaporating basin to boil off some of the water until an almost saturated solution is formed.
• this can be tested by dipping a glass rod into the solution and seeing if crystals form quickly on its surface when it is removed.
• bunsen burner is turned off and the crystals allowed to form as more water evaporates and solution cools.
• the crystals can now be removed from the mixture by filtration
  separating techniques: picture 2

Question 4

describe making pure salt from rock salt.

Answer 4

• we can use filtration and crystallisation to obtain pure salt from rock salt.
• rock salt consists of salt contaminated by various earthy or rocky impurities, which aren’t soluble in water.
• if you crush the rock salt and mix it with hot water, the salt dissolves, but the impurities don’t
• impurities can be filtered off, and remain on the filter paper
• filtrate is a salt solution
• solid salt can be obtained from solution by crystallisation

Question 5

describe simple distillation.

Answer 5

• simple distillation can be used to separate the components of a solution
• although we can use crystallisation to separate sodium chloride from a sodium chloride solution, we can also collect the water if we use simple distillation.
• the water boils and is condensed back to a liquid by the condenser
• the salt remains in the flask
• separating techniques: picture 3
• the sodium chloride solution eventually becomes so concentrated that the salt will crystallise out.

Question 6

describe fractional distillation.

Answer 6

• fractional distillation is used to separate a mixture of liquids such as ethanol and water.
• ethanol and water are completely miscible with each other
• this means that you can mix them together in any proportion and will form a single liquid layer.
• you can separate them by taking advantage of their different boiling points - water boils at 100 and ethanol boils at 78
• separating techniques: picture 4

Question 7

homogenous

Answer 7

a substance which is uniform throughout its volume.

Question 8

heterogenous

Answer 8

a substance consisting of different distinguishable parts.

Question 9

describe paper chromotography.

Answer 9

• can be used to separate a variety of mixtures
• we will usually use it to separate mixtures of coloured inks or food colourings.
• most inks and food colourings are not just made of one colour but contain a mixture of dyes.