Mixing, separating and liquid M O T I O N Why do two layers form? Why does the dye colour the water but not the oil? Why does the oil rise and fall? MAKE YOUR OWN LAVA LAMP FROM SALAD DRESSING! Water and oil do not mix. Water is more dense than oil so it sinks to the bottom while the oil floats on top. These lava lamps are made from oil, water and salt. OBJECTIVES To understand the similarities and differences in various everyday materials. To discuss the ideas of density, mixing happening? what is changing? and how is it standing at them to transfer their vote by changing? moving. GENERATING QUESTIONS ENQUIRY Give the children a few minutes quiet Manage turn taking by asking children to and floating and sinking. thinking time to reflect fully on what they have raise their hand if they want to talk. STARTER just observed and to create an individual REFLECTING ON THE ENQUIRY Play “stand to attention”. Arrange the class so that the children are sitting in a circle. Explain to the children that everyone in this game must stand up, however they must stand up individually and not at the same time as anyone else. They must work together as a group to complete the task but they must not verbally communicate with anyone: they must question based on the stimulus. Now split the class into groups of 3 and ask each member within the small group to share their question. Then together in their groups they must decide on one question they would like to discuss and record it on an A4 sheet of paper. SELECTING QUESTION FOR DISCUSSION Gather in all the questions recorded on observe others body language and try to the A4 paper and read them aloud. Place the guess when they are going to stand up. If two questions around the room and ask the or more children stand up together the group children to vote for which one they would must start from the beginning again. most like to discuss by standing next to the STIMULUS appropriate A4 sheet. The question with the Making mini lava lamps (see page 2). encourage children to describe what they see with questions like what do you see?, what is Resource for Teachers Complete the “Evaluating with emoticons” activity - see page 3. most votes will be the topic for the enquiry. Should a tie situation arise, remove the questions with fewest votes and ask anyone 1 Wa t e r a n d o i l d o n o t m i x www.ulster.ac.uk/scienceinsociety/ M I N I LAVA LAMPS To do this demonstration you will need cooking oil, food colouring, tap water, a tall glass or jar and either salt or vinegar and baking powder, or an effervescent tablet. Do either variation A or B or C. Ask the children to observe closely at each stage of the demonstration. Encourage them to describe what they are seeing in words and in pictures. VARIATION A VARIATION B Pour oil into a tall glass until it is about Pour oil into a tall glass or bottle until it a quarter full. Slowly add water until the is half full. Add water until it is three quarters glass is about three quarters full. Add drops full. Add about 10 drops of food colouring of food colouring and watch them sink (choose a colour that is easily seen e.g. red) through the oil into the water (if this and watch them sink through the oil into the happens too slowly, stir the oil and water). water (stirring if this takes too long). When When there is a good colour contrast there is a good contrast between the oil and between the oil and coloured water, pour water, drop an effervescent tablet into the some salt onto the oil (about the size of half oil. a peanut at a time). VARIATION C Pour oil into a tall glass or bottle until it is half full. Dilute some vinegar so that it is about one part vinegar to 10 parts water. Add this dilute vinegar to the oil until the jar is three quarters full. Drop some baking powder into the oil - just enough so that it sinks slowly through the oil (about the size of half a peanut). Observe! What happens to the oil/water/dye/ salt/tablet? Children can make their own mini lava lamps, investigating the science of colour, mixing, floating and sinking, chemical reactions (version B) and dissolving. Following the enquiry, the demonstration can be recorded and children asked to write a script to explain an aspect of the science. This What changes? can be used as a formal assessment. Resource for Teachers 2 For next time... try adding a coloured ice cube to the glass of oil and water. Watch as it melts. www.ulster.ac.uk/scienceinsociety/ evaluating with Emoticons Images © Microsoft Clip Art Cut out and laminate the emoticons below and place them face-up on the floor (you may need multiple copies). Ask students to reflect on how they felt during the enquiry, and why, and ask them to select the emoticon that best represents their feelings. Discuss as a class a) what was positive about the enquiry and b) how the group could improve their enquiry skills. You may want to provide blank laminated paper and a marker for students who cannot find an appropriate emoticon. Resource for Teachers 3 www.ulster.ac.uk/scienceinsociety/ FLOATING AND SINKING L AVA L A M P S MIXING Water and oil hate each other and don’t mix (no matter how hard you shake them!) The oil is always on top because it is less dense than water. When you add the food colouring, it sinks through the oil because it weighs more than an equal volume of oil (it is denser). The food colouring likes to be with water (they are both polar liquids; oil is non-polar) so only the water is coloured. Oil The food colouring diffuses (spreads out) when it reaches the water. This is because the particles that make up the water and food colouring are in constant random motion. VERSION A Salt is more dense than oil so when you pour it in, it sinks - but it brings some oil with it. When the salt reaches the water, it begins to dissolve and lets the less dense oil float back to the surface. This accounts for the bubbles of oil you see travelling through the coloured water. Water Only a limited amount of salt can dissolve in water. After the addition of a lot of salt, the water becomes saturated: no more will dissolve. The salt begins to build up at the bottom of the jar. VERSION B The effervescent (fizzy) tablet contains an acid and a carbonate in solid form. When they are solid they don’t react, but when they dissolve in water they react to release carbon dioxide. Carbon dioxide is a gas, and when it is released in water it forms bubbles. The bubbles float in both water and oil. As oil and water do not mix the bubbles rise to the top of the glass where they pop and the remaining water sinks back down to the bottom of the glass. Oil and water do not mix: they are immiscible. This is because water is polar and oil is not. Oil floats on water because it is less dense than water. Food colouring is polar like water. It sinks through the oil without mixing until it reaches the water. VERSION C The baking powder sinks through the oil into the vinegar. When it reaches the vinegar, it starts to react, producing bubbles of carbon dioxide gas. These rise through the vinegar and oil to the air, where they burst. REAL LAVA LAMPS In a real lava lamp, wax is held in oil. Cold wax is less dense than oil so it sinks. Hot wax is less dense than oil so it floats. Cold wax is heated by the bulb at the bottom, reducing its density. This makes it float in the oil. As it rises, it cools, making it more dense than oil, so it sinks again. Foo sinks d colouri ng thro into the w ugh the diffu ater, wh oil ses ( ere i throu spreads) t gh t wate he r. Resource for Teachers 4 Oil containing Carbon Dioxide Effervescent Tablet Carbon Dioxide Bubbles In version B, the tablet releases carbon dioxide gas. The gas forms bubbles which rise through the water and oil. www.ulster.ac.uk/scienceinsociety/