Published on Mar 28, 2020 Show AbstractThe objective: Evaporate water to form salt crystals. Research Questions:Salt, a mineral with the main component being sodium chloride, or NaCl, has been used for millennia to help preserve food (and make it tasty!). In ancient times, salt was used as a form of currency in some cultures. During the period when the ancient Phoenicians controlled the salt trade in the Mediterranean, salt was as expensive as gold! In this lab, we will learn how to separate salt from water through a solar process—you can use the sun to evaporate water, leaving behind the salt. Materials:a) Baking sheet b) Black paper c) Salt d) Water e) Cooking pot Experimental Procedure1. If you do not have a source of salt water (such as water from the ocean), then mix salt and water in a cooking pot until all the salt has dissolved. Your goal is to make a fairy concentrated solution of salt and water. 2. Lay the black paper on the baking sheet. Why is it important to use black paper? 3. Pour the salt water into the baking sheet, making sure to cover the black paper. 4 . Set the baking sheet somewhere warm, like outside in the sun or on a table by a window. 5. Record your observations over a number of days until all the water is gone. ResultsSalt crystals will be left over once all the water has evaporated. Why?The color black absorbs all frequencies of visible light, which will helps the light energiz e the water molecules which evaporate when they get hot. It is important that the pan is somewhere warm, because the water will more evaporate into the air more quickly. As the water evaporates, the salt doesn’t leave with it! Therefore, the concentration of salt in the water left behind increases. Eventually, the concentration gets so high that the water becomes supersaturated, and the salt will begin to recrystalliz e into a solid. When all of the water is gone, you will have salt! The same process is done on a very large scale, worldwide. A common method involves allowing seawater to flow into shallow flat beds through channels that are then sealed off. The sun heats the water until all of it evaporates, leaving mountains of salt behind. The salt is then collected and cleaned. Salt’s a particularly important mineral because it isn’t just used for cooking—it’s an essential ingredient in agriculture, science, and countless industrial products. Science Fair Project : Grade Level: Middle School;In this class experiment, students separate a mixture of sand and salt, illustrating the fundamental means of separating a mixture of an insoluble material from one that is soluble This is a very straightforward experiment. It can be carried out individually or in groups of two. Pupils must stand up during heating activities and beware of hot salt spitting when evaporation is almost complete. EquipmentApparatus
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Teaching notesIf desired, the experiment can be extended to isolate dry samples of sand and salt. To do this, the damp sand in the filter paper can be transferred to another sheet of dry filter paper, and, by folding and dabbing, the sample can be dried. If necessary, another piece of filter paper can be used. Students often like to present their specimens in small bottles for approval, so a spatula could be used to accomplish this. While the first student of a pair is transferring the sand, the other can be scraping the dried salt from the evaporating dish and transferring it to another specimen bottle. If this extension is carried out, the students should be encouraged to label the bottles. They should be told that all samples prepared in this way need to be labelled, even if in this case, it should be obvious which substance is which. Student questions
If you teach primary science, the following information is designed to help you use this resource. Skill developmentChildren will develop their working scientifically skills by:
Learning outcomesChildren will:
Concepts supportedChildren will learn:
Suggested activity useThis activity can be used as a whole-class investigation, with children working in small groups or pairs to look at how to separate the salt and sand. This could provide a stimulus for further investigations looking at how to separate other mixtures of solids, either of different particle sizes or by solubility. Primary schools often don’t have Bunsen burners, so viable alternatives need to be sourced. Similarly, it may be difficult to source the equipment needed to evaporate water to recover the dissolved salt. Head stands and tea lights can work well as possible alternatives. When carrying out this activity be aware that some insoluble solids are able to form suspensions. This is where the particles appear to have dissolved, when in fact they have been spread out throughout the liquid. A good indicator that a suspension has formed is that the liquid will go cloudy or the particles can be heard scraping as the mixture is stirred. The layout of this activity is very prescriptive as the procedure is set out on a step by step basis. An open challenge activity, with children working in small groups and devising their own methods, would extend the children’s thinking. Different groups’ suggestions could be compared and evaluated as a class. |