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Other compounds are made from different combinations of atoms, like water… carbon dioxide… and table salt. VOICEOVER: Zach has a bowl of ice cubes with a mass of five hundred grams. After some time the ice cubes melt, but the scales still show five hundred grams. This is because melting the ice has not created or destroyed any atoms and the mass has stayed the same. This is known as the law of conservation of mass. It applies to both chemical reactions and physical changes. Elements can be placed into a reactivity series with the most reactive element at the top of the list and the least reactive at the bottom. A displacement reaction occurs when a more reactive element displaces, or pushes out, a less reactive element from a compound that contains the less reactive element. After a displacement reaction, the less reactive element is now pure and left uncombined. In industry, we use iron to displace copper from solutions of waste copper compounds, which is really useful. As scrap iron is much less valuable than copper, which we need for many electronic devices such as computers and phones. VOICEOVER: The particles that make up gases and liquids move randomly. This movement allows the action of diffusion to happen.
Cel: Well, that the copper is less reactive than magnesium because it couldn't displace the magnesium. This happens because some pigments are more soluble than others. The more soluble the pigment is, the longer it stays dissolved in the water and the further it travels up the paper.
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Mrs Roberts: Yeah. So, a displacement reaction involves a metal and a compound of a different metal. In a displacement reaction a more reactive metal will displace, which means pushes out, a less reactive metal from its compound. Dr. Tim: That's exactly right, Ben. A substance is classed as insoluble if it does not fully dissolved in a specific solvent - in this case it's the sand is insoluble in water. Now, why don't you try and filter out that sand from the water. Although in the case of plastics, the individual components are molecules containing mostly carbon and hydrogen. And the key thing is that they can join together to form long chains. In the example above (the reaction between copper and oxygen to make copper oxide), we get this in the first step:
Mrs Roberts: Yes. So if we were to categorise metals by their reactivity, the most reactive metal would naturally be at the top. So, if I'm going to test you now. So, if a copper is added to a solution of magnesium chloride no reaction occurs. What does that tell you about the reactivity between copper compared to magnesium? Miss Armit: The particle model as a way of explaining the way particles move and collide. There's four things you need to know about it. All substances are made of particles. The particles are attracted to each other - some more than others. And the particles are constantly moving with what's called 'Kinetic Energy'. As temperature increases, this kinetic energy increases so they can move around more.Draw a horizontal line with a pencil and ruler about 1 cm above the bottom of a piece of chromatography paper. Everything we can see and touch, and quite a lot that we can’t as well, is made of tiny particles called atoms. And the products of oil and gas refineries were hydrocarbons, containing exactly the kind of molecules that could join up to make plastics.
Only handle the heater by the outer casing. Where possible, avoid handling the heater once it is switched on. Give the heater time to cool after it is switched off. Miss Roberts: So, when you freeze water a physical change happens, because it turns from water to ice. But, the interesting thing is that although the water changes to ice the mass will stay the same. So, earlier I froze an identical bottle with three hundred grams of water. What do you see? Katie: Well, what I see there is that it's increased. You know, the ice fills up more of the bottle. So, surely the mass has increased, proving science wrong? Gethin : I got all excited because I thought Miss Armit brought in sweets and balloons for a bit of a party. But that's not the case, it's actually for an experiment. But, how and why have you brought them in? And what's it got to do with the particle model? This part is a water-cooled condenser. There’s a hollow tube through the middle, and a sleeve around the outside. When we connect the bottom part to the tap, it fills with cold water, which flows out the top. That helps to keep it nice and cool around the central tube.
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We’ll put the Bunsen burner under here and a cylinder to collect the water formed as the water vapour condenses.
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