Separation Techniques

In the Previous Chapter…

• You’ve learned about the difference between mixtures and compounds

• You’ve also learned that one type of mixture is called a solution

• In this chapter, we will discuss more about mixtures, and how to separate their constituent parts

Topics

• Magnetic Separation• Filtration• Evaporation• Distillation• Paper Chromatography• Our Drinking Water

Magnetic Separation

• Used when trying to separate solids which can be attracted to magnets (i.e. magnetic materials) from other non-magnetic solids/liquids

• Used in garbage sorting (for recycling), iron mining (sorting of iron ore), etc.

• https://www.youtube.com/watch?v=cs6iJavFJiI

Filtration

• Used when trying to separate an insoluble solid from a liquid

• You will do this in the lab using a filter funnel and filter paper

• Real life uses: coffee machine, water treatment (more on this later)

Evaporation

• Used when you want to recover the solute from a solution (but not the solvent)

• In the lab, this is usually done in a crucible• Real life uses: salt extraction

Distillation• Used when you want to recover the solvent from

a solution • The solute can also be recovered, but the

distillation setup is mainly for the solvent• Refer to notes for the apparatus, you are required

to know name and purpose of each apparatus• Concept: we want to boil the solvent off into

gaseous state and then re-condense it back into liquid state

• The extracted solvent is called the distillate

Distillation Apparatus

• Thermometer – to monitor temperature. The solvent will start to boil at its boiling point.

• Boiling chips – to allow more even boiling• Condenser – to condense the gaseous solvent

back into liquid state. • Note that cold water goes in from the bottom

and comes it from the top. This to allow for maximum condensation.

Fractional Distillation• Similar to normal distillation, except it is to

separate two miscible liquids• Real life use: petroleum distillation• The two liquids will boil at two different boiling

points• The liquid with lower boiling point will be

extracted first• The fractionating column is to condense the

liquid with the higher boiling point when it is evaporating (but not boiling) back into the flask

(not in syllabus)

• Q: what about immiscible liquids? How to separate them?

• A: just use a tap

Paper Chromatography• (we will also do this in the lab)• Usually chromatography is used to test and

identify constituents, rather than to separate large amount of substances

• Real life use: to identify which dyes are used in ink or food

• Concept: different dyes travel a different distance through paper (see notes)

• You can try this yourself! Put a little ink on a paper napkin, and dip on end of the napkin in water

Our Drinking Water

• Singapore has one of the most advanced water supply systems in the world, and is studied by many countries who want to learn from us

• You are required to know the 3 separation processes involved in making drinking water (but the rest is good general knowledge anyways)

4 National Taps

• We get our drinking water from 4 sources:• 1) Imported Water from Johor (untreated)• 2) Local Catchment (i.e. reservoirs)• 3) Desalinated Water from the sea• 4) Reclaimed water from waste water (i.e.

NEWater)

Drinking Water Separation Processes

• Water from Johor and reservoirs are sent to treatment plants. The main separation process used is filtration. Chemicals are also added into the water to kill bacteria and make it safe for drinking.

• Although distillation may be used in desalination plants, in Singapore, we use reverse osmosis instead.

• To make NEWater, reverse osmosis is also used.

Reverse Osmosis

• Reverse Osmosis is a very special kind of filtration process

• Instead of using physical filters (e.g. filter paper or sand), a partially permeable membrane is used as a filter

• (You can obtain such a membrane on the outer layer of a hard boiled egg)

• The filter is so good that not just bacteria, but many chemical molecules are also filtered out

Summary

• Magnetic Separation• Filtration• Evaporation• Distillation• Paper Chromatography• Our Drinking Water – Filtration, Distillation & Reverse Osmosis