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 crystals | position of tube |
| 1.00 | 50 | weird jelly | in hot water (~90'C) |
| 2.00 | 50 | looks like water | in hot water (~90'C) |
| 3.00 | 52 | looks like water | in hot water (~90'C) |
| 5.00 | 60 | looks like water | in hot water (~90'C) |
| 7.00 | 56 | looks like water | in air |
| 8.00 | 53 | looks like water | in air |
| 9.00 | 51 | looks like water | in air |
| 10.00 | 48 | looks like water | in air |
| 11.00 | 46 | looks like water | in air |
| 12.00 | 45 | looks like water | in air |
| 13.00 | 42 | looks like water | in air - crystal added |
| 14.00 | 44 | looks like water | in air |
| 15.00 | 45 | weird jelly | in air |
| 16.00 | 46 | weird jelly | in air |
| 17.00 | 47 | weird jelly | in air |
- 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.
- 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.
- Record the temperature. Leave the ice for now but check the temperature after about 2, 5 and 10 minutes.
- 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!.
- Place approximately 3 cm depth of sodium thiosulfate crystals in a clean dry test tube.
- Place the test tube in your pan of boiling water. You will need to hold it in place.CARE!
- 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.
- 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.
- Keep the tube and thermometer still but continue reading the temperature.
- 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.
- Continue watching timing and recording.
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