SEPARATION TECHNIQUESSS

Type of separation techniques

Magnetic attraction

Filtration

Evaporation

Distillation

Paper chromatography

Magnetic attraction is the technique uses a magnet to?

Uses a magnet to separate magnetic materials from non-magnetic materials

Filtration is the technique used to?

separate an INSOLUBLE solid from the liquid in a solid-liquid mixture, in which the insoluble solids in a suspension are larger in size than the liquid particles

How does filtration work?

Suspension is passed through a filter paper with tiny pores

Liquid particles < Pore size < solid particles to allow the smaller liquid particles to pass through while trapping the larger solid particles.

The trapped solid particles that remain on the filter paper are called the residue.

The liquid that passes through the filter paper is called the filtrate

Why is wood charcoal used in water filters?

Has a porous surface that can absorb liquids and dissolve gases in water

What is evaporation used for

It is used to separate dissolved solids from a solid-liquid mixture

It makes use of the fact that the solvent in a solution can vaporise at any temperature, leaving behind a residue of the solid that was dissolved in the liquid.

Can we use evaporation to separate sugar from water?

Yes, but it requires INDIRECT heating as it decomposes (breaks down) at high temperatures.

So, we will need to heat it above a water bath.

What does distillation obtain?

Obtains a pure liquid from a liquid-liquid mixture/solid-liquid mixture

What does distillation involve?

Boiling and condensation

How does distillation work?

Liquid boils to form vapour from its solution and condenses to form a pure liquid

The mixture is heated in a distilling flask until the mixture boils

The water vapour formed is allowed to escape into the condenser, where the vapour condenses

The pure liquid collected from distillation is the distillate, which flows into a conical flask.

What is the flow of water in the condenser? (from outlet of water vapour to receiver)

Water out

Water in

Where should the thermometer be placed in the apparatus?

Near the outlet of the vapour, to measure the correct boiling point of the liquid

Should not be in the liquid, as the impure solution will not have a definite boiling point

The thermometer will measure a range of temperatures, which is the mixture and not the pure substance

Why should the water inlet be near the receiver

To maximise the amount of vapour coverted into its liquid

what does boiling chips do for distillation?

Allows for smooth boiling

What are the two types of distillation?

Simple distillation and fractional distillation

What does fractional distillation separate?

Separate two or more liquids with different boiling points.

What is fractional distillation? When do we use it?

It is a special type of distillation.

Generally, components boil at less than 25 °C from each other under a pressure of one atmosphere (atm). If the difference in boiling points is greater than 25 °C, simple distillation is used.

What does the fractionating column do?

Used to separate the liquids according to the order of their vaporisation so that they get separated as they are vapourised.

Simple distillation vs fractional distillation

Simple:

Separate liquids with a larger difference in boiling points

A simple apparatus is used to separate the liquids

To get the pure form of liquid, the process must be repeated

Solvent molecules can easily be separated from the solute

E.g. purify seawater

Fractional

Separate liquids with a smaller difference in boiling points

A fractionating column is used to perform the separation

Repetition of processes is not required

Solvent molecules cannot be separated from the solute

E.g. obtain different gases from the atmosphere.

Separating funnel, how does it work on the basis of?

The density of liquids

Denser liquids will be separated from the other liquids first.

What does paper chromatography separate?

Separate small amounts of substances, especially pigments, dyes and food colourings from mixtures

What does paper chromatography make use of?

Different substances dissolve to different extents in a mixture and move up at different rates

substances that are more soluble in a solvent will move faster and move up more than the substances that are less soluble

How does paper chromatography work?

A spot of ink is applied to a piece of chromatography paper, which is then lowered into the solvent. The solvent dissolves the dye in the ink, and the dyes move up the paper together with the solvent.

The different dyes in the ink mixture travel at different rates along the paper.

At the end of the experiment, the different dyes in the ink will be separated on the chromatography paper. The paper with the different coloured spots is called a chromatogram.

Will all solvents work in paper chromatography?

no. only certain types of solvents can dissolve the components in the dye.

if not, dyes will not separate.

Why cant we use a pen to draw the line?

Pen ink may dissolve and separate, hence it can interfere with the results.

what do we use it for

identify dies in substance

test purity

Why should the dyes be above the liquid level?

Dyes will instead dissolve in the liquid and not move up the paper.

What is the advantage of paper chromatography?

A small amount of solute is needed to identify the different components present in the mixture.

Applications of separation techniques (water SG)

Purify water that are non-potable water

As SG has a limited supply of freshwater, they built a network of local catchment areas.

Rainwater, seawater and used water are then collected and treated to supply drinking water

How to obtain potable water from used water

Treat sewage water with chemicals before purifying it in order to kill any bacteria present

The techniques used to purify treated sewage water must be able to separate impurities from the water

What are the two stages of obtaining drinking water from treated sewage water?

Microfiltration

Reverse osmosis

Whatt does microfiltration do? How does microfiltration work

Removes small particles from the treated sewage water

Water passes through a semi-permeable membrane filter (with tiny pores) to trap suspended solids and most disease-causing microorganisms

The water obtained from microfiltration contains mainly dissolved salts and chemical molecules

What does reverse osmosis do, and how does it work?

This technique removes

• disease-causing micro-organisms

• dissolved salts

• chemical molecules from water

Water obtained from microfiltration is pumped at high pressures through a special membrane

The pores of this membrane are so small that only very small molecules, such as water molecules can pass through, such as water molecules, can pass through, but not disease-causing microorganisms, dissolved salts and chemical molecules.

The water obtained is free from bacteria and viruses, and also contains trace amounts of dissolved salts and chemicals

Treatment of sea water, why and what is the separation technique

It is non-potable as it contains a lot of salt

Can be treated by desalination

(distillation can be used but is expensive and requires alot of energy)

How does desalination work?

Seawater is heated in a boiling chamber to produce steam

The steam condenses as it passes through a condenser

Water is then collected as a distillate

Applications of desalination plants

Convert seawater into drinking water on ships and many dry regions of earth

Some spinach leaves were used to prepare a sample by grinding the leaves using a pestle and mortar. Alcohol was added to create a mixture of green liquids and some green solids. How to obtain the green liquid only? explain the process

Filtration. The mixture passes through a filter paper with pore sizes smaller than that of the solid particles but larger than that of the liquid particles. The paper filters the solids as residue, and allows the green liquid to pass through as filtrate.

When it was added to the top of a burette filled with a substance called silica, it travelled down and separated into 3 different bands. Two of which were the colour green (dark green and light green). Are they the same substance?

No, they travelled different distances in the medium(silica). Hence, they have different solubilities in alcohol and are different substances.

When they switched the alcohol with water, only two bands were produced. Give some reasons why

Two components can dissolve in water, but 3 components can dissolve in alcohol.

Some bands could have overlapped as the solvent (water) may not provide sufficient separation between the bands,