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Chemistry EOY notes > Seperation techniques > Flashcards

Seperation techniques Flashcards

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1
Q

What is a mixture?

A

A mixture is made up of two or more substances that are mixed but not chemically combined

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2
Q

What is a pure substance?

A

A mixture is not a pure substance.

A pure substance is made up of one single element or
compound. It is not mixed with any other substance.

Crystals are the pure form of
a substance.

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3
Q

What are the separation techniques to separate a mixture?

A 
Filtration
Evaporation to dryness
crystallisation
Using a suitable solvent
Using magnetic attraction
Simple distillation
Fractional distillation
Using a separating funnel
Paper chromatography.
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4
Q

How do you separate a mixture?

A

HOW to separate a mixture?

 Mixtures are separated based on the different
physical properties of the substances that make up a
mixture.
 A mixture has the characteristics of its constituents (the
substances it is made up of.

 Examples of physical properties: colour, attraction to
magnet, solubility, density, melting and boiling points,
conductivity

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5
Q

What is Filtration?

A

Filtration is used to separate insoluble solid
particles from a liquid .
Such a mixture is called a suspension.

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6
Q

What are the mixtures that can be separated by filtration?

A
  • sand and water
  • chalk powder and water
  • clay and water
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7
Q

Explain the separation of sand and water using filtration

A

Separation of Sand and Water
Upon filtration, the solid that
remains on the filter paper is
called the residue.

The liquid or solution that
passes through the filter paper
is called the filtrate.
(sand)

(water)

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8
Q

What are the uses of filtration?

A 
Straining tea
Washing vegetables
Separating pulps from orange juice
In vacuum cleaners
-A filter bag is used to filter dust
and dirt from the air drawn in.
Household water filters
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9
Q

Explain how filtration is used in IN WATER TREATMENT

A

Raw water is filtered by layers of
sand, gravel and pebbles to remove
insoluble solids.

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10
Q

What is evaporation to dryness?

A

Evaporation to Dryness

This is a process of obtaining a soluble solid from
a solution by heating the solution until all the
solvent has boiled off.

Example:
Separating salt (sodium chloride) and water
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11
Q

Explain the use of evaporation to dryness to separate salt from water

A

Water in the
solution is lost to
the atmosphere.

Salt remains as a
white residue in the
evaporating dish.

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12
Q

When can you not use evaporation to dryness?

A

Evaporation to dryness
cannot be used for
substances that decompose on
heating eg. sugar

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13
Q

What is crystallization?

A

Crystallization is the process of obtaining a pure solid sample
(solute) from its solution.

Examples:
hydrated copper(II)
sulfate crystals

sodium carbonate
crystals

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14
Q

How do you prepare Pure Copper(II) Sulfate

Crystals by Crystallisation?

A

Step 1:
• The solution is heated
to remove most of the
solvent (water).

• Heating is stopped
when a saturated
solution is formed.

Step 2:
• The hot, saturated solution is allowed to cool.
• The dissolved copper(II) sulfate appears as pure crystals.

A saturated solution is a solution that contains as much dissolved solute as it can at a given temperature

Rapid cooling produces small
crystals while slow cooling
produces large crystals.

Step 3:

• The crystals formed are removed by filtration. The
residue of pure crystals is washed with cold distilled
water.
• The crystals are then dried by pressing them between
pieces of filter paper.

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15
Q

What are the advantages of crystillazation?

A

Advantages of Crystallisation

(i) Can be used for solids that are unstable to strong heat.
eg. _sugar decomposes when heated strongly.

(ii) Crystals are pure

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16
Q

What are the disadvantages of crystallization?

A

Disadvantages of crystallization

(i) Procedure is tedious

(i) Only a small amount of the solute is usually
obtained as crystals. The rest still remains
dissolved in the saturated solution.

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17
Q

Elaborate on using a suitable solvent

A

Using a Suitable Solvent

To separate a mixture of two solids, we use a solvent
in which one solid is soluble in it while the other solid
is insoluble in the solvent.

Different solids dissolve in different solvents.
Some common solvents are water and ethanol.

18
Q

What are the examples of using a suitable solvent to separate mixtures?

A

Example:
Separating sodium chloride and sand

A mixture of sodium chloride and sand will result in a mixture of sodium chloride solution + sand when water is added to dissolve sodium chloride.

The filtrate when you filter a mixture of sodium chloride and sand is the sodium chloride solution while the residue of the mixture of sodium chloride is the sand and traces of sodium chloride solution.

19
Q

Explain magnetic attraction.

A

• Magnetic attraction uses a magnet to separate magnetic material from
non-magnetic material.
• Magnetic materials: iron, nickel, steel
• Non-magnetic materials: copper, gold, silver

20
Q

Where are the places where magnetic attraction is used.

A

• Magnetic attraction is used in mining industries to separate iron from non-
magnetic materials

• Magnetic attraction is used in junkyards to separate iron or steel
(reusable metal) from scrap metals.

21
Q

Elaborate on simple distillation.

A

•Simple distillation is used to separate a pure
solvent (liquid) from a solution.
•Distillation involves 2 changes of state; firstly
boiling and then followed by condensation.

Examples:
Simple distillation is used for extraction of water from:
• sea water
• salt (sodium chloride) solution
• sugar solution
22
Q

What is distillation used for?

A

Distillation is used to separate a pure liquid from a solid-liquid
mixture and a liquid-liquid mixture.

23
Q

What are the 3 steps of distillation

A 
1. The mixture
is heated
and solvent
boils. (Vaporisation)
2.The solvent  Escape as
vapour.
3.When the vapour is
cooled, it condenses
into a liquid.
(Condensation)
24
Q

How do you set up the distillation apparatus?

A 
Thermometer
bulb should be
just beside the
side arm
leading to the
condenser.
Boiling chips
are placed in
the flask to
ensure smooth
boiling.
Water enters the
condenser from the
bottom and leaves
from the top.
Condenser must be
sloping downwards.
25
Q

What are the steps of simple distillation of salt solution?

A 
1. Boiling chips
are added to
ensure smooth
boiling. Water
vaporises, rises
and enters the
condenser.
2. Water boils and becomes
vapour. Thermometer measures
temperature of the vapour.
3. Water vapour
is cooled and
condenses into
pure liquid
4. Salt will be
collected as
residue.
5. Pure water
is collected
as distillate.
26
Q

Elaborate on fractional distillation.

A

Fractional Distillation

This method can be used to separate a mixture of
miscible liquids with different boiling points.

Examples of miscible liquids are:
• Ethanol–water
• Liquid air
• Crude oil
Miscible liquids are liquids that can mix (dissolve)
completely in each other to form a solution.

27
Q

Elaborate on a seperating funnel.

A

Separating Funnel

Immiscible liquids can be separated using a
separating funnel.

Example: oil-water mixture
Liquids that do not mix together completely to form
a solution are described as immiscible.

For example: oil-water mixture

28
Q

Elaborate on paper chromatography.

A

Paper chromatography is the method of separating two
or more components that dissolve in the same solvent.

Examples:
Pigments in plants Dyes in paints Colouring in food

29
Q

What is the principle of paper chromatography?

A

Principle Behind Paper Chromatography:

Separation of a mixture into its different components
depends on the relative solubility of the component.

• The more soluble component travels faster and further
up the paper than the less soluble components.

• Identical dyes travel up the same distance and produce
the same colour on the paper when the same solvent is
used.

• A pure substance produces only one spot on the
chromatogram.

30
Q

How do you separate dyes found and green food colouring?

A
  1. Place a spot of green food
    colouring on the paper.
2. Dip the paper into a
solvent such as ethanol or
water. Ensure that the
coloured spot is above the
solvent level.
  1. The components will
    separate as the solvent
    travels up the paper.
31
Q

What is a chromatogram

A

• The chromatography paper with the separated

components is called a chromatogram.

32
Q
  1. Why must the start line be drawn with a pencil and

not with a pen?

A

Pencil lead will not dissolve in the solvent while the
dyes in ink will dissolve in the solvent and complicate
the results

33
Q
  1. Why is it is important to ensure that the position of the

original spot is above the solvent level?

A

If the original spot is below the solvent level, the
dyes will dissolve directly in the solvent and the
chromatography will not work.

34
Q

What are the uses of chromatography?

A

Uses of Chromatography

  • separate the components in a sample;
  • identify the components present in a sample;
  • identify substances;
  • determine the purity of a substance.

Note: One advantage of chromatography is that it can
be carried out using very small amounts of substances.

35
Q

How do you seperate drinking water from used water?

A

By microfiltration and reverse osmosis.

36
Q

How do you seperate drinking water from seawater?

A

By desalination

37
Q

Elaborate on microfiltration.

A

The micro-filtration membrane removes
•most disease- causing micro-organism
•suspended solids

But not

  • the dissolved salt
  • Chemical molecules
38
Q

Elaborate on reverse osmosis.

A

Used water obtained from micro-filtration is pumped at high pressure
through a partially permeable membrane

The partially permeable
membrane allows fresh water
to pass through but not

• disease –causing micro-
organism.

• the dissolved salt
• Chemical molecules
Fresh water is thus obtained.

39
Q

Elaborate on desalination.

A

Desalination : Removing dissolved salts and other waste from
seawater to obtain drinking water

Seawater undergoes vaporisation and steam undergoes condensation to obtain drinking water from sea water.

This is distilattion.

40
Q

How do you test for purity?

A

Tests for Purity
1. A pure solid has an exact / fixed / definite melting point.

• Impurities lower the melting point of a solid.

• Impurities cause melting to take place over a range
of temperatures.

  1. A pure liquid has an exact / fixed / definite boiling point.
    • Impurities raise the boiling point of a liquid.

• Impurities cause boiling to take place over a range of
temperatures.

  1. A pure substance shows only one spot on the
    chromatogram.

Chemistry EOY notes (6 decks)

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