This experiment looks in ~ the temperature of 2 cups the water as they room frozen. One cup contains pure water whilst the other contains salt water. The experiment is ideal for demonstrating exactly how salt depresses the freezing allude of water. The is additionally a good introduction to the theory of implicit heat.

You are watching: Which freezes faster water or salt water science project

It is suitable for ages 16+ and also requires some understanding of the processes affiliated in state transforms of liquids.

Equipment required

DrDAQ data loggerconnected to a PCTwo DrDAQ external temperature probes (Part no DD100)Containers because that the water (we used plastic drinking cups)SaltA freezer

If the freezer is an ext than 2 m far from the DrDAQ climate you may likewise require one or much more 5 m sensor expansion cables (Part no EL032).

Experiment setup

Fill both cup with sufficient water come cover the temperature probe. Clear the more water used the much longer the experiment will certainly take.Add salt a small at a time to one of the cup of water and stirred till it dissolves. Stop including salt as soon as the solution is saturated (ie salt will certainly not dissolve). Note the cup that has salt water so that it deserve to be identified later.We placed both cups into a cardboard box with two reduced out holes. This stops the water spilling and likewise provides part insulation.Put one temperature probe in each cup the water and secure in location with a rubber band about the cup. Ideally each probe should be in the middle of the cup and also not touching the edges.Plug the probes into DrDAQ and also run PicoLog software. Surname one channel ‘Pure Water’ and the other ‘Salt Water’. Examine that the temperature readings look sensible.Set up PicoLog to record one reading per minute.Place both cups into the freezer and also shut the door being cautious to feeding the cables because that the temperature sensor the end the sheet of the door there is no pulling the sensors the end of the cups.

Carrying out the experiment

Start PicoLog collecting data and display both channels on a graph. Check that the temperature native both channels begins to decrease. Permit the experiment to continue until both temperatures have actually levelled off. In ours freezer this occurred at roughly –30 °C and also took 5 hours. Note that, because of the activity of the freezer thermostat, the temperature might fluctuate slightly.

Questions and discussion of results

Print the end a graph the the results reflecting both channels. The will aid if you pick a display that shows time due to the fact that start (use the button with the tick symbol top top the graphs button bar)

Q1.Look at the trace reflecting pure water. Through looking in ~ the alters in gradient of the graph, watch if you have the right to identify the areas of the graph explained below. Because that each region fill in the time and the temperature in ~ the start of this region.

Pure waterStart timeStart temp
Cooling native room temperature in the direction of freezing0 hours
Cooling come the freezer's minimum temperature
Stable region at minimum temperature

Q2.Before the pure water starts to freeze, the temperature drops rapidly. As soon as it starts to freeze the temperature remains reasonably constant. Explain why.

Q3.At what temperature did the salt water start to freeze. Why is this reduced than because that the pure water.

Q4.Identify the part of the graph that display the freezing of the pure and salt waters. The pure water reflects a reasonably flat an ar whilst the salt water has actually a tenderness slope. Explain why. (Hint - more salt have the right to be dissolved in warmth water).

Q5.If friend look closely at the region where freeze starts friend may notice a little ‘blip’ wherein the temperature actually raised for a quick period. Why walk this happen.

Q6.Think around what happens to the temperatures of the 2 samples as they warm earlier up to room temperature. Sketch a graph that temperature versus time mirroring what girlfriend think will certainly happen.

Further study

How could the purity that the water effect the form of the graph?How would certainly the concentration that salt result the results?What outcomes would you suppose if the samples had actually been boiled fairly than frozen?Use the outcomes to calculation the latent warmth of freezing (you will need to understand the certain heat capacity of water).

view the results and see teachers" notes


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