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Exploring Diversity of Matter using Separation Techniques

Learn how different constituents of mixtures can be separated based on their physical properties using various techniques like filtration, magnetic attraction, evaporation, distillation, and paper chromatography.

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Learning Outcomes

After studying this chapter, you should be able to:

• Understand the principles behind separation techniques: magnetic attraction, filtration, evaporation, distillation and paper chromatography
• Describe how the constituents of a mixture can be separated based on their properties
• State examples of applications of separation techniques in everyday life and industries
• Appreciate that water is a precious resource and understand why we need to conserve it
• Explain how Singapore uses separation techniques to ensure a sustainable source of drinking water

As the saying goes, "waste not, want not". It is everyone's responsibility to ensure sustainable living in a world facing climate change and rapid depletion of natural resources. Separation techniques used in waste management, water purification and food safety are critical pieces of our sustainable living puzzle. These separation techniques are not only applied in the science laboratory, but also in everyday life as we shall see in this chapter.

Let's Learn

• What is the purpose of separation techniques?
• How do we choose the appropriate separation technique(s)?
• How can we apply separation techniques to obtain potable water in Singapore?

Separation Techniques

Click on any technique to learn more about its principles, process, and applications.

Filtration

Separating insoluble solids from liquids using a filter medium that allows the liquid to pass through while retaining the solid particles.

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Magnetic Attraction

Using magnetic forces to separate magnetic substances from non-magnetic substances in a mixture.

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Evaporation

Separating a soluble solid from its solution by heating the solution until the liquid evaporates, leaving the solid behind.

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Distillation

Separating mixtures of liquids with different boiling points by heating, evaporating, and then condensing the components.

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Paper Chromatography

Separating mixtures of soluble substances based on their different rates of movement through a paper medium.

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Real-World Applications

Separation techniques are fundamental to many industries and everyday applications. Here are some examples:

Water Treatment

Distillation for desalination of seawater and filtration for removing impurities from drinking water. In Singapore, NEWater is produced through microfiltration, reverse osmosis, and UV disinfection.

Food Safety

Chromatography to detect pesticides and additives in food products. The Singapore Food Agency uses gas chromatography to ensure food safety in imported and local products.

Medicine

Extraction and separation of active compounds from plants for pharmaceutical production. Crystallization is used to obtain pure active ingredients.

Mining Industry

Magnetic separation to extract valuable metals from ores, helping to preserve limited natural resources and reduce energy consumption compared to mining new metals.

Waste Management

Various techniques to separate recyclable materials and reduce environmental impact. Scrap metal recycling uses magnetic separation to recover iron and steel.

Oil Industry

Fractional distillation to separate crude oil into useful products like gasoline and kerosene. Chemical engineers working in oil refineries in Singapore use this technique.

Food Preservation

Evaporation is used to extend the shelf life of food such as ikan bilis, herbs, spices, and dried fruits by removing water content that could lead to decomposition.

Forensic Science

Chromatography helps identify inks used in forged documents and detect illegal substances. Forensic document examiners use thin-layer chromatography for analysis.

Sustainability & Conservation

Understanding separation techniques helps us appreciate why water is a precious resource and the importance of conservation.

Water Conservation

Reverse osmosis and other techniques help create potable water from previously unusable sources, but these processes require significant energy. Singapore faces challenges ensuring sustainable living and uses separation techniques holistically.

Resource Recycling

Separation techniques are vital for recycling processes, helping to extract and reuse valuable materials from waste products. This reduces waste and preserves precious natural resources.

Singapore's Water Resources

As a small island nation, Singapore faces challenges in water supply. To ensure sustainability, Singapore has developed Four National Taps:

• Water from local catchment - Rainwater collected through a network of drains and canals
• Imported water - Water from Johor, Malaysia
• NEWater - Ultra-clean, high-grade recycled water produced from treated used water
• Desalinated water - Pure drinking water obtained from seawater through reverse osmosis

Together with water conservation efforts, these sources help ensure Singapore's water security for the future.

Water Conservation Tips

Although water is readily available in Singapore, it remains a scarce resource. It is everyone's responsibility to make every drop count. Here are some ways to conserve water:

• Turn off the shower when soaping
• Wash vegetables in a container instead of running water
• Use half-flush whenever possible
• Use a water-efficient washing machine and wash with full loads
• Wash your car with water from a pail instead of a hose
• Reuse water from the washing machine to flush toilets or wash floors
• Ensure taps are turned off when brushing teeth
• Water plants with water used to wash vegetables or fruits

By understanding how separation techniques work, we can develop more sustainable approaches to water treatment, resource recovery, and waste management.

Test Your Knowledge

Check your understanding of separation techniques with this quick quiz!

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1. Which separation technique would be most appropriate for separating iron filings from sand?

Magnetic attraction

Distillation

Evaporation

Chromatography

2. Which technique involves the separation of components based on their different boiling points?

Filtration

Distillation

Magnetic separation

Paper chromatography

3. In paper chromatography, what causes different components to travel at different rates?

Different densities

Different magnetic properties

Different solubilities and attractions to the paper

Different electrical charges

4. Which technique would be most suitable for obtaining salt from seawater?

Filtration

Evaporation

Magnetic separation

Paper chromatography

5. Why is understanding separation techniques important for environmental sustainability?

They have no relation to environmental issues

They only matter for industrial processes

They only matter for laboratory work

They help in recycling, water purification, and resource conservation

6. Which of the following is NOT one of Singapore's Four National Taps?

Water from local catchment

Imported water

NEWater

Groundwater extraction

7. In the production of NEWater, which process uses ultraviolet light?

Microfiltration

Reverse osmosis

Disinfection

Distillation

8. What process would you use to separate a mixture of iron filings, salt, and sawdust?

Just filtration

Just magnetic separation

Just evaporation

A combination of magnetic separation, dissolution, filtration, and evaporation

9. Why is reverse osmosis preferred over distillation for desalination in Singapore?

It produces cleaner water

It works faster

It uses less energy and is more sustainable

It is cheaper to set up initially

10. Which of Singapore's Four National Taps involves the recycling of used water?

Water from local catchment

Imported water

NEWater

Desalinated water

11. Which separation technique is used to extend the shelf life of ikan bilis (dried anchovies)?

Evaporation

Distillation

Filtration

Chromatography

12. What is the principle behind magnetic separation?

Differences in boiling points

Differences in particle sizes

Differences in solubility

Differences in magnetic properties

13. In the NEWater production process, what technique is used in the final stage?

Reverse osmosis

Microfiltration

Ultraviolet disinfection

Chemical treatment

14. Which physical property is utilized in paper chromatography?

Density

Solubility in a solvent

Boiling point

Magnetic attraction

15. Which of the following is NOT an application of distillation?

Making perfumes

Producing distilled water

Making food flavorings

Separating iron filings from sand

16. What is the starting point for NEWater production?

Used water/wastewater from homes and industries

Rainwater from local catchment

Seawater

Imported water from Malaysia

17. In paper chromatography, what happens to substances that are more soluble in the solvent?

They remain at the starting line

They move slower up the paper

They travel further up the paper

They change color

18. Why should a pencil, not a pen, be used to draw the starting line in paper chromatography?

Pencil is more precise

Pen ink would dissolve in the solvent and affect the results

Pencil lead is magnetic

Pencil marks are required for accurate measurements

19. What is the function of boiling chips in a distillation apparatus?

To increase the boiling temperature

To cool the apparatus

To prevent bumping by ensuring smooth boiling

To filter impurities

20. In a mask that protects against COVID-19, which separation technique is applied?

Filtration

Magnetic separation

Distillation

Evaporation

21. Which of these water conservation methods is an example of "Reuse"?

Turning off the shower when soaping

Washing vegetables in a container

Using water from the washing machine to flush toilets

Using half-flush whenever possible

22. What makes NEWater safe for consumption?

Only the addition of chemicals

Only filtering through reverse osmosis

A three-step process of microfiltration, reverse osmosis, and UV disinfection

Only UV disinfection

23. In a solar still, which two processes are involved in obtaining pure water?

Filtration and magnetic attraction

Evaporation and condensation

Reverse osmosis and UV disinfection

Chromatography and distillation

24. Which of these is an application of chromatography?

Obtaining salt from seawater

Separating iron from aluminum

Identifying inks used in forged documents

Filtering water in a tea strainer

25. What is the function of the condenser in a distillation apparatus?

To heat the mixture

To separate solid particles

To cool the vapor and convert it back to liquid

To measure the temperature

26. Which natural process resembles distillation?

The water cycle

Plant respiration

Animal digestion

Soil erosion

27. When separating a mixture of iron filings, salt, and sawdust, which should be done first?

Use a magnet to remove iron filings

Add water to dissolve the salt

Use filtration to separate sawdust

Evaporate to get the salt

28. What is the name of the paper with different colored spots obtained after paper chromatography?

Color map

Chromatogram

Spectrum paper

Dye sheet

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Filtration

Principle

Process

Applications

How it Works

Filtration separates solid particles from a liquid or gas by passing the mixture through a filter medium that allows the fluid to pass through but retains the solid particles.

The process relies on different particle sizes and the pore size of the filtering medium. Particles larger than the pores are retained, while the fluid and smaller particles pass through.

Substances with different particle sizes can be separated using a sieve. A sieve has small holes called pores, which are of a particular size. Particles that are smaller than the pores pass through the sieve, while particles that are larger than the pores are retained.

Key Principles

• Based on difference in particle size
• Uses a porous barrier (filter paper, sand, etc.)
• Works with heterogeneous mixtures containing insoluble solids
• No chemical changes occur during the process
• Driving force can be gravity, pressure, or vacuum
• The liquid that passes through is called the filtrate
• The solid that remains on the filter is called the residue

Filtration Process

1. A heterogeneous mixture containing an insoluble solid and a liquid is poured onto a filter (often filter paper in a funnel)
2. The liquid (filtrate) passes through the filter paper
3. The solid particles (residue) are trapped by the filter paper
4. The filtrate is collected in a container below

Separating chalk and water using filtration. The pores of the filter paper allow water particles to pass through them. Chalk particles, which are bigger than the pores, are retained by the filter paper.

Video Demonstration

1 / 4

The filtration process begins with a mixture of insoluble substance and liquid.

2 / 4

The mixture is poured through filter paper in a funnel.

3 / 4

Large solid particles are trapped by the filter paper and become the residue.

4 / 4

Small particles and liquid pass through the filter paper pores to become the filtrate.

❮ ❯

Real-World Applications

• Water Treatment: Removal of particulate matter from drinking water. In siltation ponds, groundwater is filtered as it flows through sand and rocks of different sizes.
• Coffee Making: Separating coffee grounds from the liquid using a coffee filter or tea strainer
• Air Purification: HEPA filters removing dust and allergens
• Kidney Dialysis: Removing waste products from blood
• Industrial Processes: Separating valuable solids from waste liquids
• Health Protection: N95 respirator masks filter airborne particles, including respiratory droplets that may contain viruses
• Natural Filtration: Our nose acts as a filter. The hairs in our nostrils and mucus help trap large solid particles in the air we breathe, preventing them from entering our lungs

Applications in Singapore

In Singapore, filtration and reverse osmosis are used in the recycling of used water to obtain potable water. This process is part of the NEWater production, which provides a sustainable water source for the nation.

Magnetic Attraction

Principle

Process

Applications

How it Works

Magnetic separation uses magnetic forces to separate magnetic materials from non-magnetic materials in a mixture.

This technique relies on the inherent magnetic properties of certain materials (particularly those containing iron, nickel, or cobalt) that are attracted to a magnetic field.

Examples of magnetic substances include nickel, iron, cobalt and steel. Other substances such as plastic and paper are non-magnetic.

Key Principles

• Based on magnetic properties of materials
• Works when at least one component is magnetic
• Non-destructive separation technique
• Highly selective for magnetic materials
• Can be performed in both dry and wet conditions
• Requires no additional chemicals or heat
• Environmentally friendly separation method

Magnetic Separation Process

1. A mixture containing magnetic and non-magnetic components is spread out
2. A magnet is moved over the mixture
3. Magnetic materials are attracted to the magnet and cling to it
4. The magnet with attached magnetic materials is moved to a separate container
5. The magnetic materials are released by removing the magnetic field

For example, when a magnet is placed near a mixture of iron filings and sulfur, only iron filings are attracted to the magnet. Sulfur, which is non-magnetic, is left behind.

Video Demonstration

Real-World Applications

• Mining Industry: Separating valuable magnetic ores from gangue minerals
• Recycling: Separating ferrous metals from other waste materials. In Singapore, scrap metal is one of the many waste materials generated. Scrap metal contains a mixture of metals such as aluminum, copper and iron. Iron, which is magnetic, can be removed from the mixture by passing a strong magnet over the scrap metal.
• Food Industry: Removing metal contaminants from food products. Magnetic separators filter magnetic contaminants from food products.
• Medicine: Magnetic nanoparticles for targeted drug delivery
• Water Purification: Removing magnetic particles from industrial wastewater
• Soil Decontamination: Electromagnetic separators can remove magnetic contaminants from soil

Environmental Benefits

Recovery and recycling of iron and steel helps to preserve precious natural resources such as iron ores, which are limited. Recycling metals also requires less energy than mining new metals from metal ores.

Evaporation

Principle

Process

Applications

How it Works

Evaporation is used to separate a soluble substance (solute) from a liquid (solvent). The solvent has a lower boiling point than the solute, meaning the liquid changes into gaseous state at a lower temperature than the solute.

When all the solvent evaporates, the solute that dissolved will be left behind as a residue.

For example, salt dissolves in water to form salt solution. All of the salt solution will pass through filter paper. Hence, salt cannot be separated from water by filtration. Evaporation should be used instead.

Key Principles

• Based on differences in boiling points
• Works for solutions (homogeneous mixtures)
• Requires heat energy
• The solvent transforms from liquid to gas
• The dissolved solid remains behind as residue
• Used when the solute is the desired product
• No collection of the evaporated solvent

Evaporation Process

1. A solution containing dissolved solids is placed in an open container (like an evaporating dish)
2. The solution is heated to increase the rate of evaporation
3. The liquid gradually converts to vapor and escapes into the air
4. As the liquid evaporates, the solution becomes more concentrated
5. Eventually, all the liquid evaporates, leaving the solid solute behind

Heat is applied to the salt solution. This speeds up the change of water into water vapor. Water changes state at a lower temperature than salt. Thus, salt is left behind as the residue.

Tip: Alcohol is a volatile liquid. This means that it can change quickly into the gaseous state at room temperature without heating. Alcohol is also flammable. Direct heating of alcohol in a test tube should be avoided. A water bath should be used. This applies to any flammable solvent, such as ethanol. If a soluble solid is not heat-stable, such as sugar, it will decompose easily with strong heating.

Video Demonstration

Real-World Applications

• Salt Production: Obtaining salt from seawater in salt pans. In a salt mine, hot water is pumped deep into the ground to dissolve the salt. The salt solution is then pumped up to pans on the ground. Water in the salt solution is allowed to evaporate under the sun so that solid salt is left behind in the pans.
• Food Processing: Concentrating fruit juices and sauces
• Food Preservation: Water is essential for decomposition. In order to preserve food, water is removed using evaporation. This is widely applied in the production of herbs, spices, and dried small fishes (e.g., ikan bilis).
• Sugar Refining: Concentrating sugar solutions
• Chemical Industry: Recovering solids from solutions
• Traditional Medicine: Preparing herbal extracts

Vacuum Drying

Vacuum drying of food is carried out in a vacuum oven where air is removed. The removal of air allows water to evaporate more quickly than under normal temperature and pressure. Vacuum drying is a preferred method of food preservation as normal drying causes food to deteriorate in flavor.

Distillation

Principle

Process

Applications

How it Works

Distillation separates mixtures based on differences in the boiling points of the components. When a mixture is heated, the component with the lower boiling point vaporizes first.

The vapor is then cooled and condensed back into a liquid in a separate container, effectively separating it from the other components.

Distillation involves both evaporation and condensation. The boiling point of the liquid is usually very much lower than that of the dissolved solid. The temperature of the liquid remains constant at the boiling point until all the liquid has vaporized.

Key Principles

• Based on differences in boiling points
• Involves both evaporation and condensation
• Works best for liquids with significantly different boiling points
• The vapor is collected and condensed (unlike simple evaporation)
• Can be performed at various pressures to improve separation
• The condensed liquid is called the distillate
• Used when the volatile component is the desired product

Distillation Process

1. Place the mixture of liquid (e.g., seawater) in the distillation flask containing some boiling chips. The boiling chips ensure that the liquid boils without bumping.
2. Heat the mixture until the temperature reaches the boiling point of water.
3. Place the bulb of a thermometer at the opening of the arm of the distillation flask to measure the boiling point of the vapor distilled.
4. At the boiling point of water, water vapor leaves the distillation flask and passes through the condenser where it is cooled.
5. The condenser is cooled by a continuous flow of cooler water from the water tap, entering from the bottom and leaving from the top.
6. Collect the condensed liquid in the conical flask as the distillate.

In this setup, salt solution in the distillation flask is heated until it boils. Water changes into steam which passes through the condenser. The condenser has cold water running through it continuously to cool the vapor. The water vapor condenses into pure water (distillate) which is collected in the conical flask.

Fun Fact

Boiling chips help to smoothen the boiling process in the distillation flask. For example, they prevent the distillation flask from shaking too much during boiling.

Video Demonstration

Real-World Applications

• Petroleum Refining: Fractional distillation to separate crude oil into different products
• Alcohol Production: Distilling fermented solutions to produce spirits
• Water Purification: Desalination of seawater to obtain drinking water
• Essential Oil Extraction: Steam distillation of plant materials to obtain perfumes. One of the earliest uses of distillation is perfume making. Plant parts such as petals are boiled in water. The vapor collected as the distillate is then made into perfumes.
• Industrial Chemicals: Purification of solvents and reagents
• Food Flavoring: Citrus oil and liquid extracts of herbs and spices are obtained by distillation. These can be used in food flavorings.

Scientific Endeavour

Distillation has been used in many civilizations since a very long time ago. The first mention of simple distillation appeared in India and China in around 800 BC. Distillation was used in the production of beer and rice wine. Over the years, as scientific knowledge evolved, this separation technique improved.

Desalination in Singapore

Do you remember how we can get pure water from salt solution using distillation? We need to heat the salt solution. Since a large amount of fuel is required to heat a big volume of seawater, this process uses up a lot of energy and is thus unsustainable. In Singapore, desalination is carried out using reverse osmosis instead of distillation.

Does distillation remind you of a similar process in nature? The water cycle also involves heating (evaporation) and cooling (condensation). A solar still involves similar processes as the water cycle. It can be used to collect water in places where water supply is irregular.

Paper Chromatography

Principle

Process

Applications

How it Works

Paper chromatography separates mixtures based on the different rates at which components travel up a piece of paper due to differences in their attraction to the paper (stationary phase) and the solvent (mobile phase).

Components that are more attracted to the paper move more slowly, while those more attracted to the solvent move faster, creating separation bands.

Different substances in a mixture dissolve to different extents in a solvent. Substances that are more soluble in the solvent travel longer distances from the starting point. Substances that are insoluble in the solvent remain at the starting point.

Key Principles

• Based on differential adsorption and solubility
• Uses a stationary phase (paper) and mobile phase (solvent)
• Components separate based on their partition coefficient
• Works well for colored compounds or those that can be visualized
• A simple but powerful analytical technique
• Can be used to test the purity of a substance
• Different solvents can be used to achieve optimal separation

Paper Chromatography Process

1. A drop of the sample is placed on the starting line drawn with a pencil
2. The chromatography paper is placed in the solvent with the starting line above the solvent level
3. As the solvent moves up the paper, the different components travel up the paper to different extents
4. The paper is removed and dried, and the separated components are visible as separate spots
5. The paper with the different colored spots is called a chromatogram

In paper chromatography, the solvent travels up a chromatography paper and substances that are more soluble in a solvent will travel further from the starting point than substances that are less soluble. A chromatogram showing the separated components of a mixture is obtained at the end.

Fun Fact

In Greek, the word "chrom" means "color" and "graphy" means "writing". If a sample is pure, only one spot will be seen on the chromatogram when run with different solvents.

Video Demonstration

Real-World Applications

• Forensic Science: Analyzing ink in forged documents. Forensic document examiners use thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) to examine ink samples and prove whether they are similar or dissimilar.
• Pharmaceutical Industry: Determining purity of drugs
• Food Industry: Detecting food dyes and additives. Chromatography can be used to identify permitted food colorings used in food dyes and food products.
• Biochemistry: Separating amino acids and proteins
• Environmental Science: Identifying pollutants in water and soil. Environmental agencies use separation techniques such as paper chromatography to ensure that water is clean.
• Anti-Doping Testing: It helps to detect the use of illegal drugs by athletes.

Science @ Work: Scientist Ensuring Food Safety

Scientists in the Singapore Food Agency (SFA) carry out several tests on food items that are imported or sold in local supermarkets to ensure that they are safe for consumption. Gas chromatography, which uses a gas as a solvent, is one of the methods used to separate substances in food items.

Tip: Chromatography is used to separate colored substances, such as dyes, inks and pigments. It can also be used to separate colorless substances. Locating agents are then added to react with the colorless spots to form colored products. The identities of the components in the mixture can then be determined by comparing against standard references.

Sublimation

Principle

Process

Applications

How it Works

Sublimation is the process in which a solid changes directly into a gas without becoming a liquid. This method is used to separate a solid substance that sublimes from those that do not.

Substances that go through sublimation include iodine and dry ice (solid carbon dioxide). A pure solid sublimes at a fixed temperature.

Key Principles

• Based on the ability of certain solids to change directly to gas
• Requires heating below the melting point
• The sublimed vapor condenses back to solid on a cooler surface
• No liquid phase is involved in the process
• Works for volatile solids with high vapor pressure
• Suitable for heat-sensitive compounds

Sublimation Process

1. A mixture containing a substance that can sublime is placed in a container
2. The mixture is gently heated
3. The sublimable substance changes directly from solid to vapor
4. The vapor rises and comes into contact with a cool surface
5. The vapor condenses back to solid on the cool surface
6. The non-sublimable substances remain in the original container

To separate sodium chloride from iodine, for example, heat the mixture as shown in the diagram. On warming, iodine sublimes and produces a violet vapor that solidifies on the cooler part of the funnel.

Real-World Applications

• Dry Ice: Solid carbon dioxide (dry ice) sublimes at room temperature and is used for refrigeration and special effects
• Pest Control: Naphthalene balls (moth balls) sublime slowly at room temperature, releasing vapors that repel insects
• Pharmaceutical Purification: Separation of volatile medicinal compounds from non-volatile impurities
• Food Preservation: Freeze-drying (lyophilization) removes water through sublimation
• Chemical Analysis: Purification of organic compounds for analytical purposes

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