chapter 4 notes ‘exploring diversity of matter by its separation techniques’.pdf

HILLGROVE SECONDARY SCHOOL SCIENCE DEPARTMENT SECONDARY ONE SCIENCE 2/3 CHAPTER 4: EXPLORING DIVERSITY OF MATTER USING SEPARATION TECHNIQUES (Answers)...

HILLGROVE SECONDARY SCHOOL SCIENCE DEPARTMENT SECONDARY ONE SCIENCE 2/3 CHAPTER 4: EXPLORING DIVERSITY OF MATTER USING SEPARATION TECHNIQUES (Answers) Name: __________________________ Class: 1 – ___ Date: ___________ By the end of this chapter, you should be able to: No. Learning outcomes Tick 1 Explain how the constituents of a mixture can be separated based on their properties, using the following techniques: magnetic attraction, filtration, evaporation to dryness, distillation, paper chromatography. 2 State some examples of the applications of the various separation techniques in everyday life and industries, e.g., water treatment (i.e., distillation or *reverse osmosis of sea water in desalination plants, and filtration and *reverse osmosis of treated used water), food safety and waste management. 3 Investigate the separation of constituents of mixtures based on basic principles involved in the following separation techniques: magnetic attraction, filtration, evaporation, distillation and paper chromatography 4 Show an appreciation of why water is a precious resource and the need to conserve it. 5 Show an appreciation of how Singapore uses separation techniques to ensure a sustainable source of potable water. 1. Purpose of separation techniques 1.1 Why do we need to separate mixtures?  Many mixtures contain useful substances which need to be separated before they can be used.  The constituents of a mixture can be separated by physical methods known as separation techniques.  The choice of separation technique depends on the physical properties of the constituents of the mixture. [Refer to AB 4.1.1 (page 95-96)] 1 2. Separation techniques 2.1 Magnetic attraction  A magnet is used to separate magnetic substances from non-magnetic substances.  Examples of magnetic substances: steel, iron, nickel and cobalt.  Application: o A strong magnet is used to separate iron from scrap metal. The iron obtained can then be reused or recycled. This helps to reduce waste. 2.2 Filtration  Filtration is used to separate an insoluble solid from a liquid.  Examples of mixtures which can be separated by filtration: o Sand and water o Chalk powder and water o Mud and water  Why is the liquid able to pass through the filter paper but not the insoluble solid? o The insoluble solid particles are too large to pass through the pores of the filter paper. o The liquid particles are small enough to pass through the pores of the filter paper. The solid that remains on the filter paper is called the residue. The liquid that passes through the filter paper is called the filtrate. 2   Applications: o A tea strainer separates tea leaves from tea. o In a siltation pond, groundwater is filtered as it flows through the holes between the sand and rocks of different sizes, allowing clean water to be obtained. o The hairs and mucus in our nose trap dust particles in the air we breathe in to prevent them from entering our lungs. 2.3 Evaporation to dryness  Evaporation to dryness is used to obtain a soluble solid (solute) from a solution by heating.  Example: to obtain salt (sodium chloride) from salt solution or seawater. evaporating dish o Water evaporates to become water vapour. o Salt is left behind as the residue.  Applications: o Food preservation (e.g., ikan bilis, wolfberries, herbs). o In some countries, salt is produced in salt pans by evaporation to dryness using heat from the sun. Checkpoint 1 Q1. Name a suitable method for separating each of the following: (a) Water from muddy water: filtration (b) Iron filings from sand: magnetic attraction (c) Salt from seawater: evaporation to dryness 3 2.4 Simple distillation  Simple distillation is used to separate a pure solvent (liquid) from a solution through boiling and condensation.  Example: to obtain water from salt solution. o In the distillation flask, water boils and becomes water vapour. o In the condenser, water vapour cools and condenses into pure water. o Pure water is collected as the distillate.  Applications: o Making perfumes. o Producing distilled water. o Making food flavourings. o Obtaining drinking water from seawater through desalination. Checkpoint 2 Q1. State the reading on the thermometer as water distils over: 100 °C Q2. On the diagram above, draw a cross (X) to show where the salt from salt solution would be left after all the water has distilled over. 4 2.5 Paper chromatography  Paper chromatography is used to separate small amounts of substances with different solubilities in the same solvent.  Example: separating dyes found in black ink. o Procedure:  Draw the start line using a pencil.  Place a drop of black ink on the start line.  Dip the filter paper into a solvent (e.g., water or ethanol). Ensure that the black ink spot is above the solvent level.  The components will separate as the solvent travels up the filter paper. o Conclusions:  Black ink is a mixture of 4 types of dyes (i.e., it is not pure).  Yellow dye is the most soluble in the solvent because it travelled the longest distance, followed by green dye and then red dye.  Grey dye is insoluble in the solvent because it remained at the start line.  Applications: o To identify dyes in ink. o To check for presence of banned substances in food. o To check for presence of drugs in urine. o To detect water pollutants. 5 Checkpoint 3 Q1. Paper chromatography was performed on a sample of food colouring (X) and 4 banned dyes (A, B, C and D). If X contains any of the 4 banned dyes, it is not safe for consumption. (a) Identify the dye(s) that are pure: A and B (b) Identify the banned dyes(s) present in X: B and C (c) State and explain whether X is safe for consumption. It is not safe for consumption because it contains banned dyes B and C. 2.6 Summary of separation techniques [Refer to AB 4.2.1 (page 97-108)] [Homework: AB 4.2.2 (page 109-114)] 6 3. Application of separation techniques to obtain potable water in Singapore 3.1 Importance of water  Water is essential to life.  All living things require water to stay alive.  Water has many uses: o Homes: drinking, cooking, washing and cleaning. o Industries: to make, process, wash, dilute, cool and transport products. o Activities: swimming and canoeing. 3.2 Sources of water in Singapore (Four National Taps)  Rainwater from local catchment and imported water Rainwater collected Transported to water Tap water in rivers and purification plants reservoirs + water Filtration imported from Malaysia Insoluble impurities (e.g., sand and mud) are removed.  NEWater Wastewater Transported to water purification from homes and NEWater plants industries Microfiltration Microscopic particles and bacteria are removed. Reverse osmosis Undesirable contaminants (e.g., viruses) are removed. Ultraviolet disinfection Any remaining bacteria and viruses are destroyed. 7   Desalinated water Seawater Transported to desalination plants Pure water Distillation Reverse osmosis Seawater is heated to Seawater is pumped through produce water vapour. partially permeable membranes which have very small pores. Water vapour is condensed into pure water. The pores allow water particles to pass through but not salt Disadvantage: particles or microorganisms. Costly as a large amount of fuel is required to heat up the seawater. [Refer to AB 4.3.1 (page 115-116)] [Homework: AB Practice Questions (page 117-120)] 8