Chapter 7 : Separation Techniques Let 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 <ul><li>show an awareness of basic principles involved in some separation techniques </li></ul><ul><li>explain how the properties of constituents are used to separate them from a mixture </li></ul><ul><li>show an awareness of the applications of the various separation techniques in everyday life and industries </li></ul><ul><li>show an awareness of the techniques involved in obtaining pure water from sea water in desalination plants </li></ul><ul><li>use separation techniques (filtration, distillation, paper chromatography) </li></ul><ul><li>show an appreciation of the systematic investigation involved in the study of substance </li></ul><ul><li>show an appreciation that water is a precious resource and we need to conserve it </li></ul>
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 evaporation Separation by filtration Separation by magnetic attraction Separation 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 suspension In 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 Evaporation Evaporation = 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 dish pipe clay triangle tripod stand Bunsen burner watchglass beaker water boiling chips wire gauze tripod 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. heat distillate The solution is heated
7.5 Separation by Paper Chromatography Separation by = Separate and identify Paper Chromatography the different coloured components in mixtures Paper 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
<ul><li>Paper chromatography is often used to identify rather than to obtain the components contained in mixtures such as dyes. </li></ul><ul><li>Fractional distillation can be used to separate these components. </li></ul>Fractional distillation Did You Know ? ? ?
7.6 Obtaining Pure Water from Seawater To 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 water Undergoes boiling Undergoes condensation Do 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 pressure partially 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 - NEWater Used water undergoes many processes to become NEWater: Used water Conventional wastewater treatment Microfiltration Reverse osmosis UV irradiation NEWater <ul><li>Solids are removed by filtration </li></ul><ul><li>Dissolved solids are converted into solid mass and removed by filtration </li></ul><ul><li>Water is passed through membranes to remove most solids and bacteria </li></ul><ul><li>Pressurised water passes through partially permeable membrane </li></ul><ul><li>Water is free from salt and bacteria </li></ul><ul><li>Water is further disinfected by UV irradiation </li></ul>