Ch07 separation techniques

Chapter 7 : Separation

TechniquesLet me give you a test. How can you separate the ice and water from a cup of ice water?

Now this should be easy. Give me a minute to think about it. HMMM…..

2 hours later…

HMMM…..Alright. I give up. To separate them, you just have to scoop the ice up from the cup of ice water

Lesson Outcomes• show an awareness of basic principles involved in some separation techniques

• explain how the properties of constituents are used to separate them from a mixture

• show an awareness of the applications of the various separation techniques in everyday life and industries

• show an awareness of the techniques involved in obtaining pure water from sea water in desalination plants

• use separation techniques (filtration, distillation, paper chromatography)

• show an appreciation of the systematic investigation involved in the study of substance

• show an appreciation that water is a precious resource and we need to conserve it

Separation Techniques

We are going to study a few separation techniques, which includes evaporation, magnetic attraction, filtration, distillation and paper chromatography.Are you able to fit the above separation techniques into the our everyday lives and industries?

Drying of clothes

Separating gold

Identifying colours in candy

Separation by

evaporationSeparation by

filtration

Separation by magnetic

attractionSeparation by

chromatography

Separating tea from tea leaves

We must find a difference in the properties of the constituents that make up the mixture to be able to separate them.

For example: how do you separate sulphur and iron?

Difference in their properties : non-magnetic and magnetic material

Separation technique: Magnetic attraction

What is the difference in their properties

Choose an appropriate separation technique

7.1 Separation by Magnetic Attraction

Separation by magnetic attraction = Uses magnet to separate magnetic material from non-magnetic

material

Mixture of iron and sand

iron (magnetic object)

sand (non-magnetic object)

Magnetic separation

Examples of magnetic materials: iron, nickel, steel

Examples of non-magnetic materials: copper, gold, silver

Magnetic separation is used in mining industry and in junkyards

It is used to separate iron from non-magnetic materials

It is used to separate steel (reusable metal) from scrap yards

7.2 Separation by Filtration

Separation by Filtration = Separate insoluble solids from a liquid in a solid-liquid suspensionIn filtration: insoluble solid (trapped in filter) = residue

fluids (passes through filter) = filtrate

residue

filtrate

Filtration with a piece of filter paper

Water purification plant

Filtration is used in water treatment plants where raw water is filtered by sand filters to remove solid particles and obtain clear water

Raw water

Filtered water

Boiling to dryness

Evaporation using steam bath

7.3 Separation by EvaporationEvaporation = Separate dissolved solids (solutes) from a liquid or solvent in a solid-liquid solution

Salt can be obtained by evaporating seawater.

Through evaporation, the seawater (solution) is heated until all liquid (solvent) evaporates and leaves the dissolved solids (solutes) as residue.Two types of evaporation techniques are commonly used in laboratories

evaporating dishpipe clay triangletripod stand

Bunsen burner

watchglassbeakerwaterboiling chipswire gauzetripod stand

Bunsen burner

Used when solute left behind is not easily decomposed under temperatures higher than 100 °C

Used when solute is unstable and decomposes easily at temperatures higher than 100 °C

7.4 Separation by Distillation

Distillation = 1. Separate solvent from a solution

2. Separate solutions of two liquids (based on their different boiling points)

In distillation: a solution is heated so that its solvent boils and escapes as vapour. The vapour is then cooled and condensed into a liquid (distillate)

cooling water out

cooling water in

When the vapour is cooled, it turns into a liquid.

distillate

The solution is heated

heat

7.5 Separation by Paper ChromatographySeparation by = Separate and identify Paper Chromatography the different coloured

components in mixturesPaper chromatography: components in the

mixture which are more soluble in the same solvent travel further on the chromatography paper.

Different coloured components will appear at different locations because they travel at different rates It can be used for

testing food colourings to ensure that a product is suitable for consumption

It can be used for detecting the presence of drugs in urine samples

Go to Video 7.1

• Paper chromatography is often used to identify rather than to obtain the components contained in mixtures such as dyes.

Did You Know???

• Fractional distillation can be used to separate these components.

Fractional distillation

7.6 Obtaining Pure Water from SeawaterTo meet the increasing demand for water in Singapore, she opened her first desalination plant in Tuas in 2005.

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

Distillation

Seawater

Steam Fresh waterUndergoes boiling

Undergoes condensatio

nDo you find the above process familiar? It is similar to the distillation process we conduct in school laboratories.

Desalination plant

The process of distillation may be simple but a lot of heat is produced from the burning of fossil fuels. Hence, this method is often very expensive.

Reverse Osmosis

Another method used in desalination plants is reverse osmosis.Reverse osmosis: Pressurised seawater is forced through a partially permeable membrane

pressurepartially permeable membrane

salt and waste particles remain water flow

The partially permeable membrane allows fresh water to pass through but not the dissolved salt or other waste particles.

Fresh water is thus obtained.

7.7 Obtaining Pure Water from Used Water - NEWaterUsed water undergoes many processes to become

NEWater:Used water

Conventional wastewater treatment

Microfiltration

Reverse osmosis

UV irradiationNEWater

•Solids are removed by filtration

•Dissolved solids are converted into solid mass and removed by filtration

•Water is passed through membranes to remove most solids and bacteria

•Pressurised water passes through partially permeable membrane

•Water is free from salt and bacteria

• Water is further disinfected by UV irradiation