Methods of Separating Mixtures Magnet Filter Settling Decant Evaporation Chromatography Distillation

Separating mixtures If we add 10g of salt to 50g of seawater, how much would the mixture weigh? How much salt would be recovered if we separated this mixture by evaporation?

Magnets What types of materials will magnets attract? Magnets will attract IRON, STEEL (NICKEL and COBALT as well). How could you separate a mixture of sulphur and iron filings? By using a MAGNET! Separating iron and sulphur 1. mixture of iron and sulphur and a magnet. 2. Wrap the magnet in a paper-towel. 3. Use the magnet to separate the iron filings from the sulphur. Questions 1. What did you observe? 2. Could you use a magnet to separate gold and sulphur? The iron filings are attracted to the magnet. No, gold is not magnetic.

Settling Separating sand and water 1. Fill a beaker with water. 2. Add some sand to the water. 3. Stir the sand using a glass rod. What do you observe? 4. Wait a couple of minutes. What can you see now? What happened? The sand particles are pulled to the base of the beaker by GRAVITY. Extension activity Repeat the experiment above but instead of just sand use a mixture of sand and gravel. What do you observe?

Decanting Separating sand and water 1. Take a beaker containing water with sand settled at the bottom. 2. Carefully pour away the water whilst trying not to disturb the sand. 3. How clean is the water you have poured off (decanted)? Is there a better method of separating sand and water? It is very difficult using the decanting method to obtain pure water that contains no sand particles. There is a better way of separating sand and water, we will look at that next.

Filtration

Filtration separates a liquid from a solid Mixture of solid and liquid Stirring rod Filtrate (liquid component of the mixture) Filter paper traps solid Funnel Filtration separates a liquid from a solid

Separating Mixtures

Exercise 1: Filtrate and Residue 1. Which substance was left on the filter paper (this is called the RESIDUE)? 2. Which substance passed through the filter paper (this is called the FILTRATE)? 3. Could you use the filtration method to separate salt and water? The sand was the residue. Water was the filtrate. No, salt is soluble in water and would therefore pass through the filter paper with the water. Filtrate

Paper Chromatography http://www.moe.gov.sg/edumall/tl/digital_resources/chemistry/images/paper_chromatography.jpg

Chromatography Tie-dye t-shirt Black pen ink DNA testing Crime scene Paternity testing

Chromatography 1. Take a piece of filter paper and draw a large dot in the middle with a coloured felt-tip pen. 2. Then using a dropper add a couple of drops of water onto the ink dot. 3. Note your observations. What did you observe? The ink drop separates out into its component colours. The pattern you get depends upon the colour of felt-tip pen you use.

Exercise 5: Chromatography 1. Four coloured felt-tip pens produce the ink patterns below. a) Which ink dot contains only one colour? b) Which ink dot contains three colours? c) Which two ink dots contain two colours? A D B & C

Evaporation When wet clothes are left on a washing line they eventually become dry. Why? The water on the clothes evaporates (changes from a liquid into a gas). How could you use a similar method to separate salt and water? If you heat a solution of salt and water and then leave it for a few days the water will EVAPORATE and leave the salt behind. Separating salt and water 1. Your teacher will give you a solution of salt and water. 2. Set up the apparatus as shown on the right. 3. Pour some of the solution into the evaporation dish. 4. Place the evaporation dish onto the gauze. 5. Heat the solution for 30 seconds using a blue Bunsen flame. 6. Let the evaporation dish cool and then leave in a safe place for a few days. 7. After a few days note down your observations.

Setup to heat a solution Ring stand Beaker Wire gauze Ring Bunsen burner

Separating Mixtures

Distillation Separating salt and water 1. Your teacher will give you a solution of salt and water. 2. Set up the apparatus as shown below. Leibig Condenser 3. Add some of the solution into the flask. Delivery tube 4. Fit the delivery tube and bung into the conical flask. 5. Heat the solution using a blue Bunsen flame. 6. Note your observations. Bung Distillate

A Distillation Apparatus liquid with a solid dissolved in it thermometer condenser tube distilling flask pure liquid receiving hose connected to cold water faucet “A Distillation Apparatus”   Description: This transparency shows an apparatus used for laboratory distillations. Basic Concepts The separation of substances by distillation occurs because the boiling point of the substances differ. The substance with the lowest boiling point boils away first. Distillation is based on the principle that a substance will change from a liquid to a vapor during heating and from a vapor back to a liquid while cooling. Teaching Strategies Use this slide to explain to students how a distillation apparatus is used to purify liquids and to separate the components of liquid mixtures. Begin by reviewing the phases of matter, stressing the processes of evaporation and condensation. Remind students that different liquids have different boiling points. Point out that substances that are solids at room temperature usually have higher boiling points than do substances that are liquids at room temperature. Questions If the distilling flask shown in the diagram were open to the air (rather than being connected to the condensor), what would happen to each component of the mixture in the flask as boiling continued? Explain your answer to question 1 in terms of the boiling points of the liquid and the dissolved solid. In the distillation apparatus, the vaporized liquid must enter the condenser. The condenser consists of a long tube within another tube (the jacket). The substance in the central tube and the jacket cannot mix. Cold water enters at the bottom of the jacket and exits at the top. What is the function of the condenser jacket? How would changing the length of the condenser jacket affect how well it performs this function? Explain why the liquid entering the receiving flask is pure. To separate a mixture of methanol and water, you set up a distillation apparatus and heat the mixture to the boiling point of methanol, 65 oC. What substance would you expect to collect at the receiving flask? When you finish the experiment, you discover that the substance in the receiving flask is not pure. It still contains both water and methanol. Can you explain why? (Hint: Think about vapor pressures.) Before automobiles were invented, crude petroleum was used mainly as a source of kerosene. The petroleum was heated in a device called a still. Gasoline, then considered to be useless, evaporated first into the air. Kerosene boiled off next and was condensed and collected. A tar-like residue remained in the still. From this information, what can you deduce about the boiling points of gasoline, kerosene, and the residue? How will you know when all of one component has been separated?

The solution is boiled and steam is driven off.

Salt remains after all water is boiled off.

No chemical change occurs when salt water is distilled. Saltwater solution (homogeneous mixture) Distillation (physical method) Salt Pure water

Separation of a sand-saltwater mixture.

Separation of Sand from Salt Gently break up your salt-crusted sand with a plastic spoon. Follow this flowchart to make a complete separation. Salt- crusted sand. Weigh the mixture. Pour into heat-resistant container. Fill with water. Stir and let settle 1 minute. Dry sand. Calculate weight of salt. Weigh sand. Decant clear liquid. No How does this flow chart insure a complete separation? Wet sand. Evaporate to dryness. Repeat 3 times? Yes

Separating mixtures How would you get salt from seawater? Evaporate the water and the salt is left behind. This is exactly how the salt that can be found on the ground (or under it) was formed. Seas that evaporated MILLIONS of years ago, left the salt behind.

Exercise 6: Link the Separation Techniques Chromatography Iron and sulphur Evaporation Sand and water Distillation Ink from water Filtration Salt from water Colours in brown ink Magnet