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Science help please

Discussion in 'Primary' started by Lo77ee, Jul 8, 2012.

  1. I am trying to plan a lesson for a year 3 class aiming to teach them that some solids can melt when heated and that some liquids can solidify when cooled. I want to put it into the context of Charlie and the chocolate factory but I am struggling to think of a suitable 'fair test' that the children could set up in this context......any ideas would be greatly appreciated.
    Many thanks :)[​IMG]
     
  2. I am trying to plan a lesson for a year 3 class aiming to teach them that some solids can melt when heated and that some liquids can solidify when cooled. I want to put it into the context of Charlie and the chocolate factory but I am struggling to think of a suitable 'fair test' that the children could set up in this context......any ideas would be greatly appreciated.
    Many thanks :)[​IMG]
     
  3. natbar

    natbar New commenter

    Chocolate for melting and cream or ice cream?
    This can be made quickly in the classroom by puting the cream in a sandwich bag and then putting this bag into a sandwich bag filled with ice, add salt to the ice and it freezes in about 10 mins.
    Both can be reversed so as a plenary you can make toast and discuss how the other two processes can be reversed but this one can not.
    The fair test part cold be the amont of time given to allow both proceses to happen? chocolate in a sandwich bag sumbereged in quite warm water (not sure the max temp that they are allowed to work with) give 15 mins time for both. Both processes have happened due to water frozen and warm and temperature.
    yummy ice cream and melted chocolate for a science treat after!! [​IMG]
     
  4. Fair test, change only one thing, keep everything else the same and decide what you want to measure. So you are going to need quite a bit of equipment. If you want to cool and melt chocolate I guess it would be easiest to use chocolate buttons. You can change the quantity of chocolate, the temperature, the time, the heat source, the type of chocolate (white, dark, milk or all one type but different brands) However as chocolate melts so easily and I am assuming you won't have very sophisticated measuring equipment it may be hard to get any really great results. Water baths at freezing, 15 degrees, 30 degrees and 40 degrees will give a reasonable result. You might need to try a few at home first. Perhaps use washing up type basins with different temperatures of water in them and a pyrex bowl or plastic take away container floating in the water. Should allow enough kids to get around it.

    The things you could measure could be the temperature of the chocolate so you will need a thermometer or candy thermometer. Or the quantity - scales with gram measurements. The time - stopwatch or microwave clock. The power or amount of heat - power level of microwave or temperature of water used to immerse container with chocolate in it.

    You usually melt chocolate over boiling water to stop it going grainy, this can be very dangerous with small people as steam is so dangerous and pots can tip. I have done it by using an electric slow cooker and half filling it with water and then placing a heatproof pyrex jug in the middle with the chocolate buttons inside. Measure the temp of the water every minute or so... as it heats up. Sometimes the buttons look sold but when you stir them they are melted. You will have to work on a definition of what is melted... soft or really runny.

    If you can have a microwave in the classroom you can also do a specified amount of chocolate for a specified number of seconds, 10, 20, 30, 40. ... usually can't do much less than ten second increments and see how many seconds it takes to melt.

    Or set specified quantity of chocolate and specified amount of time such as 40 seconds, but change the power setting from high, to medium to defrost and see what the results are. The problem is that the melting point of chocolate is quite low about 34 degrees celsius so it is solid at room temp but melts at body temp (or in the mouth).

    Perhaps they could time how long it takes to melt in their hand!!! My kids when little used to do that inadvertantly. Or place chocolate in different locations around the school and see if it melts and take the ambient room temp. Bit easier to do in Australia in the summer where you can get some pretty high temps in and around school, may be more tricky on a cool day in Britian.

    For the turning a liquid to solid take a specified quantity of melted chocolate and place in different types of cold water, freezing water (but not soldi) and on ice... the conduction will not be as high with the solid ice as with the icy slurry. Measure the time it takes for certain amount of chocolcate to become solid again. Perhaps you could use those little medicine cups with a lolly stick in them and the kids will end up with a chocolate pop to eat.

    Of course any experiment with chocolate is very difficult to get the kids to concentrate on the big science concepts, they really only want to eat it!!
     

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