Separating mixtures Mixtures can be easily separated. There are several different methods depending on what is to be separated. Over the next few pages are several methods, stick in the picture that goes with the notes.

Sieving: This is an easy way of separating big from small. The small parts fall through the sieve.

Sorting: Another easy way to separate a mixture. Works best if the objects are large enough to pick up easily. You can sort according to colour, size or shape etc.

magnetism This is one of the easier methods to separate metals from non-metals (or from non-magnetic chemicals) The metal (usually iron) is attracted to the magnet.

Mini experiment Using a magnet and plastic Petri dish, separate iron filings from a mixture of sand and iron filings. magnet Iron filings sand Plastic petrie dish

filtering This is similar to sieving. It removes a solid from a liquid. The pore sizes in the filter paper allow the liquid through but not the solid. 2 liquids can’t be separated in this way, only a liquid and a solid Mini experiment: Separating sand and water. Copy and complete the work from the board

decanting This is a way of removing a liquid from a solid. Often used when there are solid particles that will sink to the bottom. Decanting is also used when pouring off home brew beer so as not to get the solid particles floating in the bottom of the bottle in the drinking glass. Task: follow the teachers instructions to have a go at decanting.

chromatography In paper chromatography, a liquid sample flows up a vertical strip of adsorbent paper, on which the components (usually seen as colours) are deposited in different locations. Each colour comes to a halt at different heights because of the speed they travel. Chromatography is used in forensics for many chemicals. E.g. deciding on pen inks, unknown smells etc. Each chemical has a signature, it always comes out of a mixture in the same place each time. Often on CSI programmes you will see this as peaks on a graph, with each peak representing a different chemical.

evaporation This method uses the sun or some other heat source to remove water from a solution (dissolved solid e.g. salt). The solid is left behind as the water evaporates. This is the method that is used to produce table salt in NZ from sea-water. At Grassmere the sea water is placed in large shallow pool, the sun (and wind) evaporate the water, leaving the salt behind. The salt is removed and dried further in the sun then prepared for sale.

Distillation This method is used to separate 2 liquids, or a dissolved solid from a liquid. Distillation works through the fact that different liquids have different boiling points. The first liquid to reach boiling point turns into a gas and rises to the top of the distillation column, it is then cooled and becomes a liquid again and drips out of the condenser. Draw the diagram off the board, it will take a full page.

Teacher demo: We can see distillation in the teacher demo. A mixture of vinegar and water are to be separated using this method. Water boils at 100 o C, whereas vinegar boils at 118 o C. This means that the water will be the first to turn into a gas and will come out from the condenser. What came out of the condenser? _____________ With a home distillation unit, the idea is to produce pure water by separating tap water from the impurities in it. The water is evaporated and rises away from the impurities. The steam is then cooled and pure water occurs.

Problem: 1. List the steps you would take to separate out a mixture of sand, iron filings and salt. Describe how each step works to separate the three substances in the mixture. 2. Sand, saw dust, salt and water have been mixed together. Describe the steps you would take to separate and collect each of the substances. For each step, say how it works to separate out the substance

Pg 14 & 15 should be completed. Mark your own work. Pg complete and mark. No book: copy and complete the following: Write the name of the separation method: _______________: liquid is boiled off, leaving crystals behind _______________: the colours in ink are separated because they move at different speeds. _______________: a magnet attracts particles of iron _______________: liquid is boiled off a solution and condenses on a cold surface _______________: a liquid is separated from a solid as it passes through filter paper