© KCL. WCED. PENTECH Cherries and chains1 Here are some juicy cherriesHere is some iron chain In time, the cherries will get eaten and the chain will go rusty. Both the digestion of the cherries, as food, and the rusting of the iron, are chemical reactions. Chemists study chemical reactions. A chemical reaction occurs when the atoms in a substance re-combine with other atoms to form new substances. Scientists think that everything in the universe is made of atoms. Different types of atom form different chemical elements. The elements are often displayed in a special chart called the periodic table. Some substances contain more than one element, others don’t. The iron chain is made from the element iron and contains only iron atoms. Although the cherries will contain a small amount of iron, they are made of different elements: mostly carbon, hydrogen, oxygen and nitrogen. What’s the link ? MAKE a poster that shows what everything in the universe is made from.

© KCL. WCED. PENTECH Cherries and chains In school, Sikili and Solani are doing an experiment to investigate the chemical reaction of the rusting of iron. They have collected three glass test tubes. In the first test tube they have put an iron nail with a small amount of water. In the second tube they have put a nail with some calcium chloride given to them by their teacher. The calcium chloride is a chemical that keeps the nail dry. Lastly, the third tube contains a nail covered with boiled water. A small amount of paraffin oil has been floated on the boiled water. This keeps the air from getting to either the water or the nail. SKETCH a diagram to show how they have set up their experiment 2

© KCL. WCED. PENTECH Cherries and chains Sikili and Solani left their test tubes for four days. Here are the results of their chemistry experiment. They have marked if rust has been produced on the nails 3 In the tube Test tube 1Test tube 2Test tube 3 Water Air    x x DECIDE on what they can now conclude from these results. DESCRIBE the evidence for such conclusions. DISCUSS what they must do to show that oxygen, rather than air, is involved in rusting. Rust  xx

© KCL. WCED. PENTECH Cherries and chains 4 Here is a diagram from a chemistry textbook Iron Rust plus Oxygen Vibrating iron atoms Moving oxygen atoms Molecules of rust Writing equations 3Fe + 2O 2  Fe 3 O 4 changes to Looking at substances Thinking of atoms Use the diagram to EXPLAIN rusting in terms of atoms. Represents atoms of the element iron Number of atoms Number of that type of atom in the molecule Represents a molecule of oxygen Represents a molecule of rust Number of molecules

© KCL. WCED. PENTECH Cherries and chains5 To stop the chemical reaction that leads to iron rusting both water and the oxygen in the air must not be allowed to come into contact with the iron. There are several different ways of doing this. TechniqueAdvantages Disadvantages Coating in oil Cheap, quick and easyRubs off easily Not water resistant Painting Chrome platting Rusts under scratches Galvanizing by dipping in zinc Moderately expensive Very expensiveWater resistant Shinny looks is attractive Hard to scratch Water repellent Lots of possible colours Water resistant Good over large areas Lasts well Use the information above to DRAW a picture showing how the parts of a car are protected from rusting. LABEL the different forms of rust protection.

© KCL. WCED. PENTECH Cherries and chains6 Cherries contain different chemicals made from different elements. After digestion many of these chemicals are stored in the liver. In the liver one of the chemicals of importance is glucose - C 6 H 12 O 6. Glucose is a form of sugar. The glucose and the oxygen combine in the cells of your body to give energy. The energy enables the cells to function. The glucose is carried to the cells by your blood stream. The oxygen in the air is absorbed into the blood stream in your lungs. When the oxygen and glucose react, in a chemical reaction, water and carbon dioxide are produced. The carbon dioxide is carried away from the cells of your body, back to your lungs, by your blood stream. SKETCH a diagram of the human body. SHOW on your diagram the information given in the text above.

© KCL. WCED. PENTECH Cherries and chains Fresh air sucked in to the lungs Stale air blown out from the lungs Carbon dioxide indicator Change of colour Indicates carbon dioxide present From the diagrams WRITE a description of how this experiment works. Here are illustrations that show how to see if carbon dioxide gas is present in the air going into and, coming out from, the lungs. 7

© KCL. WCED. PENTECH Cherries and chains8 Here is a diagram from a biology textbook Sugar plus Oxygen Writing equations C 6 H 12 O 6 + 6O 2  6H 2 O + 6CO 2 + energy changes to Looking at substances Thinking of atoms Use the diagram to EXPLAIN respiration in terms of atoms. Number of that type of atom in the molecule Represents a molecule of glucose sugar Number of molecules of oxygen Water plus Carbon dioxide