Melting or freezing?

You will need:
  • Access to almost boiling water
  • Jam jar ( remove labels if possible)
  • test tube
  • petri dish
  • supply of sodium thiosulfate crystals (DDS)
  • -10' to 100'C thermometer (DDS)
  • sodium thiosulfate crystals (DDS)
  • empty baked bean can (DDS)
  • Sodium bicarbonate powder (DDS) (aka "bicarbonate of soda")
  • Citric acid crystals (DDS)
  • electronic scales if available
  • Circular filter papers if available
  • Supply of ice cubes
  • Supply of salt
Time/ minutes Temperature /'C appearance of crystalsposition of tube
1.00 50 weird jellyin hot water (~90'C)
2.0050looks like waterin hot water  (~90'C)
3.0052looks like waterin hot water  (~90'C)
5.0060looks like waterin hot water  (~90'C)
7.0056looks like waterin air
8.0053looks like waterin air
9.0051looks like waterin air
10.0048looks like waterin air
11.0046looks like waterin air
12.0045looks like waterin air
13.0042looks like waterin air - crystal added
14.0044looks like waterin air 
15.0045weird jellyin air 
16.0046weird jellyin air 
17.0047weird jellyin air 
  1. Hold the thermometer in the palm of your hand and watch the level of the liquid in it change. Record the temperature when it stops changing.
  2.  Half fill a small beaker with some of your ice cubes. Put a tiny amount of tap water in so there is enough water in the bottom of the beaker to cover the thermometer bulb. 
  3. Record the temperature. Leave  the ice for now but check the temperature after about 2, 5 and 10 minutes. 
  4. Heat up a small pan of water on your cooker. CARE!. Use the thermometer to check the temperature.Turn off the heat when the water has reached 90'C VERY HOT!. 
  5. Place approximately 3 cm depth of sodium thiosulfate crystals in a clean dry test tube.
  6. Place the test tube in your pan of boiling water. You will need to hold it in place.CARE!
  7. Use the thermometer to measure the temperature of the sodium thiosulfate. Record the temperature of the crystals and say what they look like ( their appearance). Try to do this once every minute.
  8. When all the crystals have gone, remove the tube from the hot water and allow it to cool. Keep recording the time, the temperature and the appearance of the contents of the tube.
  9. Keep the tube and thermometer still but continue reading the temperature. 
  10. When the liquid in the tube has got to 40'C carefully take one crystal of sodium thiosulfate and add it to the contents of the test tube.
  11. Continue watching timing and recording.


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Monday, 08 March 2021

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