Data logger, oscilloscope, signal generator and more!

DrDAQ is a versatile instrument that connects to the USB port of any PC. Using the supplied PicoScope software it can be used as an oscilloscope, spectrum analyzer and signal generator.

From just £95

Find out more  

Freezing of pure and salt water 


Confession — these answers are by Pico technical staff, none of whom will admit to having been in a physics or chemistry lesson for a few years. Please check these answers before use. We would be grateful to anyone who can email us with suggestions of better questions and answers!

Graph showing the results obtained for both freezing and melting

Graph showing the results we obtained for both freezing and melting.


Q1. Look at the trace showing pure water. By looking at the changes in gradient of the graph, see if you can identify the regions of the graph described below. For each region fill in the time and the temperature at the start of this region.
A1. The answers will obviously depend on the students graph.

Q2. Before the pure water begins to freeze, the temperature drops rapidly. Once it begins to freeze the temperature remains fairly constant. Explain why. 
A2. The temperature remains constant as the water is absorbing the latent heat of freezing.

Q3. At what temperature did the salt water begin to freeze. Why is this lower than the pure water.
A3. The temperature again will depend on the students results. We are not sure why salt water freezes at a lower temperature — please let us know if you have a good explanation!

Q4. Identify the sections of the graph that show the freezing of the pure and salt waters. The pure water shows a fairly flat region whilst the salt water has a sharper gradient. Explain why. 
A4. As the solution of salt water begins to freeze, the water freezes (as pure water) so the remaining solution becomes more concentrated (again we are not sure about this answer).

Q5. If you look carefully at the region where freezing starts you may notice a small ‘blip’ where the temperature actually increased for a short period. Why did this happen. 
A5. As the liquids begin to freeze, there must be an exothermic reaction.

Q6. Think about what happens to the temperatures of the two samples as they warm back up to room temperature. Sketch a graph of temperature against time showing what you think will happen.
A6. Our graph above shows what happens during melting.

Teachers’ notes

The experiment does not take long to prepare, but will take a few hours to carry out. For this reason some planning is required. Either start the experiment first thing in the morning, or alternatively start in the afternoon and leave to run overnight (this will require the PC to be left running).

It is possible that the purity of the water may have an effect on the results, we had good results using bottled mineral water, tap water may not work as well.

Credits, comments and further info

This experiment was written by Pico Technology. Please contact us if you have any comments about this experiment or suggestions for improvements.


  • The kit (2408B) is of obvious quality, easy to setup and calibrate and the free to download software has a reasonable learning curve. Superb kit, superb support, what more can I say.

    Rop Honnor
  • I have been using my 4224 PicoScope for years. I travel abroad so this has been ideal due to its physical size. Storage of waveforms on my Laptop is very easy allowing me to quickly email waveforms to my Colleagues.

  • Not many USB scopes works on Win & Mac & Linux too, so that proves me that guys from Pico really cares about us, customers. This made my decision much easier when I was looking to buy an USB scope.

    Raul Trifan
  • We have been using Picoscope 6404D for quite some time, and are amazed by its accuracy and powerful emulations while working with numerous signal evaluations.

    J Mohanty
  • PicoLog TC-08: This is a very nice unit that works consistently and reliably.

    Jeff Hulett
  • It is a great scope. I had a weird problem - it did not work on one of my PC’s. Customer service gave me first class service. If I could give 6 stars for customer service - I would do so.

    Niels Larsen
  • Perfect Partner for Development of Encoder controlled Stepper Motor Actuators. Since the included software is really stable, this type of device is a great tool for great tasks!

    Helmut Schoettner
  • A superb piece of equipment worth its weight in gold

    Nigel Clinch
  • So simple to use & beats any other I have ever used hands down.

    John D Samsing
  • Rather than webcam our benchtop scope screen, it was suggested we use a PicoScope to share waveforms via screen share.

    We were a bit hesitant at first … but it worked flawlessly, and everybody is now out shopping for PicoScopes!

    T Lövskog • SVP of Innovation at Additude AB
  • Great functionality in a compact size. I really like moving the mouse pointer to a position and having the Time and Voltage display the values at that point. Calibration equipment is a breeze with that feature.

    Don Horein

PC oscilloscope and data logger products