Methods of seperating and purifying

Question 1

The composition of a pure substance:

Answer 1

• Cannot be changed

- Is the same in all parts of a piece of the substance

Question 2

Mixture

Answer 2

• Contains elements and/or compounds that are not chemically joined together.
• You can use physical processes to seperate mixtures into different substances

Question 3

Filters

Answer 3

• Can be used to separate some mixtures

- They let smaller pieces or liquids through but trap bigger pieces or insoluble substance

Question 4

Solution

Answer 4

• A mixture made of solutes in a solvent

Question 5

Solute

Answer 5

Dissolved substance

Question 6

Solvent

Answer 6

Liquid that solutes dissolve it

Question 7

Saturated solution

Answer 7

Contains the maximum amount of solute that can dissolve in that amount of solvent

Question 8

Rf value

Answer 8

Distance moved by spot/distance moved by solvent

Question 9

Distillation

Answer 9

• Used to separate a solvent from a solution (e.g water and sea water)
• The solution is heated
• The solvent boils
• Solvent vapor passes into the condenser
• The vapor is cooled and condensed back to the liquid state
• The liquid is collected in a beaker

Question 10

Fractional distillation

Answer 10

• You use fractional distillation to separate: a liquid from a mixture of miscible liquids (e.g ethanol and water)
• The mixture is heated
• The mixture boils
• Hot vapor rises up the fractionating column
• Vapor condenses when it hits the cool surface of the column and drips back
• The fraction with the lowest boiling point reaches the top of the column first
• It’s vapor passes into the condenser and is collected in a beaker

Question 11

Filtration

Answer 11

• You can use filtration to separate an insoluble substance from a liquid or a solution
• The solution is passed through the filter in the funnel.
• The solvent and solute pass through the fine holes to form the filtrate
• Bits of insoluble substances cannot fit through the holes so leave a residue in the filter paper

Question 12

Crystallization

Answer 12

You can use crystallization to produce: solid crystals from a solution.

• The solution is heated to remove enough solvent to produce a saturated solution (one that cannot hold any more solute)
• The saturated solution is allowed to cool
• Crystals form in the solution
• The crystals are separated from the liquid and dried

Question 13

Paper chromatography

Answer 13

Works because some compounds dissolve better in solvent than others

When a solvent moves along the paper, it carries the difference substances in the mixture at different speeds, so they are separated

The solvent is called the mobile phase
The paper contains the stationary phase

Question 14

Core practical- investigating inks

Answer 14

Aim: to use simple distillation to separate a sample of the solvent in some ink. Use paper chromatography to separate the colored substances in samples of ink

Method:

• Heat the flask of ink using a bunsen burner, making sure it simmers gently
• Continue heating until you have collected a few cm^3 of distillate
• Note the maximum temperature obtained
• Draw a pencil line on a piece of chromatography paper, about 2cm from the bottom
• Add a small spot of ink to the pencil line
• Add water to a container with a depth of about 1cm
• Place the paper into the container. Make sure the paper is supported.
• Take the paper out before the water reaches the top and mark the solvent front with pencil
• Calculate Rf

Question 15

Desalination

Answer 15

Producing pure water from sea water (simple distillation)

Question 16

Aquifers

Answer 16

Underground rocks containing groundwater

Question 17

Fresh water from natural sources contain

Answer 17

Objects such as leaves and twigs

Small insoluble particles such as grit and silt

Soluble substances including sales, pesticides, and fetal users

Bacteria and other micro-organisms

Question 18

Making drinking water

Answer 18

• Sedimentation (small particles are allowed to settle out)
• Filtration (tanks with beds of sand and gravel)
• Chlorination