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Middle Years Science Program
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"Mad
Scientist Show"
(Prep-3) Return to Science Shows  Program: St Anne's. Presentation: Topics: "Bubble Chemistry" Equipment:
Theory: 1. The lemonade has dissolved sodium carbonate in it. This makes the mixture basic (the opposite to acidic). Acids tend to give off charged hydrogen ions. The more they give off the more dangerous they are. Bases tend to absorb charged hydrogen ions and in just the same way can be dangerous. The reaction of a base and acid causes all the fizz. There is a huge amount of carbon dioxide gas given off (ie. the fizz). By breaking up the icecream before adding lemonade and then stirring really quickly speeds up the reaction and makes it froth more. "Reaction and Change" Equipment:
Theory: 1. A physical reaction is one that allows the substance to return easily to its original state (eg. ice melting and then freezing it again back to ice). Some of the above materials will melt and therefore can return upon cooling back to their original state (eg. butter, candle wax and ice) whereas some will burn. The process of burning is when a substance is heated the chemical structure changes permanently and no amount of cooling will return it back to its original state (eg. cheese will go brown and then burn; sugar will turn to toffee and then burn). 2. The properties of corn flour are the key in this activity. Most liquids behave like water. Fluids, which flow easily, has a low viscosity (eg water flows easily compared with Golden Syrup which has a high viscosity). Isaac Newton described the behaviour of normal liquids and we call them Newtonian fluids. This slime is what we call a non-Newtonian liquid; other examples are tomato sauce and quick sand. Slime doesn't behave like a normal liquid, it is made up of tiny, solid particles of cornstarch suspended in water, and chemists call this type of mixture a colloid. It is nice and runny when we stir it gently, but quite firm if you hit it hard or try to stir it too fast. Slime behaves like this because when you apply pressure to it, its viscosity increases and the slime becomes harder. "Mixing Things" Equipment:
Theory: 1. Oil and water are different types of molecules. There exists in nature two general types of molecules: oil-like molecules and water-like molecules. Water-like molecules have a positive end and a negative end and are more likely to be able to conduct electricity through it more easily. They can react with each other more easily since a negative end of one water-like molecules attracts the positive end of another water-like molecule. Oil-like molecules do not have a positive or negative end but are neutral at both ends. Similarly, oil-like molecules react only with other oil-like molecules. This is why oil and water do not mix ... they cannot react with each other very easily. Detergent molecules on the other hand are made up of a very long chain of carbon atoms ... one end has both positive and negative parts (making this end a water-like molecule) and the other end neutral (making it an oil-like molecule). When detergent is mixed with clothing in the wash, the oil-like end can dissolve and wash away the oil-like dirt and the water-like end can dissolve and wash away the water-like dirt. Brilliant hey? 2. This strange phenonema is due to surface tension. On the top surface of water in any container the water molecules are crowded together packed up against each other. The detergent molecule is a much much larger and denser molecule than water. So when the drop of detergent drops into the reservior all the detergent molecules that are packed together much much more densely than the water realise that outside the boat there is a lot more room to move. They literally "push" the water molecules out of their way as they burst out the back end of the boat. This effect propels the boat forward. It is like a whole class going on an excursion by train to the city. As soon as the doors of an almost empty train open at a station the students burst in and spread themselves along the full length of the carriage in a hurry. 3. Viscosity is the measure of "thickness" of a liquid. The measure of viscosity is to do with the interaction of molecules with each other on the microscopic level. If the molecules that make up the mixture are very long then on the microscopic level they may tangle easily. This would make the mixture harder to pour and therefore increase the viscosity. If there were greater bonds between molecules then the same thing will happen. Bonds are forces that exist as a result of molecules having charges. Sometimes molecules may have a positive end and a negative end on them (in much the same way as static electricity makes clothes cling to you). As a result of this the positive end of one molecules attracts the negative end of another therefore creating a bond. This force of attraction tends to stop external forces from "tearing" these two molecules apart. The greater the forces the less likely movement away from each other is possible. In most of the substances above the size of the molecules is most important. Liquids like water and lemonade are made up of molecules that are no more than 3 atoms joined together. Some of the others (eg. vegetable oil) can have 20-60 atoms joined together ... they are massive molecules with respect to the sizes that we are concerned with.
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