THE EFFECT OF SALT ON THE TIME IT TAKES ICE TO MELT

THE EFFECT OF SALT ON THE TIME IT TAKES ICE TO MELT Isabella Carswell (Year 7) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500

Results:

Discussion

This investigation, that aimed to determine the effect of different amounts of salt (sodium chloride) on ice, found that the more salt (sodium chloride) that was placed on the ice cube, the faster it melted. In other words, the ice melted more slowly with less salt (sodium chloride) on it. A plot graph (see above) of the two variables in the experiment (amount of salt and average time of ice melting) showed the data had a clear negative relationship and a line of best fit suggested a linear trend. In other words, the data shows a decreasing straight line that is directly related to the increase in salt placed on the ice decreases the time taken to melt. Therefore, the results supported the original hypothesis that the ice cube with the most salt (sodium chloride) added will melt faster. People who live in snowy conditions, such as the Northern Hemisphere, use salt to melt ice on roads so that the roads are safer to drive on, but why does this happen? Salt (sodium chloride) lowers the freezing point of water making it impossible to freeze at 0 degrees Celsius with salt on it. This is because the salt particles interfere with the water (H2O) particles obstructing them from bonding and forming ice. When you dissolve table salt (sodium chloride) in water the sodium and chloride ions separate so the particles become small and move in between the water (H2O) molecules. The reason the more salt (sodium chloride) added to the ice cube creates a difference in the time it took to melt in my experiment, is because the more salt in or on the water/ice, the lower the freezing point becomes making the 1tsp of saltwater melt faster as its freezing point is further away from zero degrees, the usual freezing point of water.

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The results in this experiment are considered reliable as the results collected were consistent when repeated under the same conditions (e.g., 46 min, 46min, 47min for a tsp of salt on top) and are consistent with primary sources of results (Mrs Baird’s results). Even though the results are predominantly reliable they could be monitored more closely and to the exact second instead of being rounded up. This could be done by making the timing include seconds or even milliseconds if exact results are needed.

The results were not considered valid as some variables such as where the salt is poured into the test container (some of the salt may have fallen off the ice cube on to the container surface). The size of the ice cubes was not controlled, as they weren’t measured for size consistency before testing, but were of a similar size. The salt (sodium chloride) when poured, would fall onto the ice and bounce off into the surrounding tray making the measurement slightly off. One of the ice cubes for the ½ tsp of salt was broken which affected the time it took to melt as it was smaller than the others. As mentioned, the ice cubes were not the exact same size but roughly similar. This size difference would affect the time they took to melt.

The accuracy of this experiment could be improved by ensuring that the ice had completely melted. It was difficult to tell if the ice was still there or if it had melted entirely and instead of ice there were bubbles, which were deceiving. Parallax errors were difficult to avoid as it was difficult to know that the ice had completely melted. There are many things that could have been done to improve the results and method of this experiment. One could be always having full attention on the ice cubes and watching them consistently until they melt or recording a video of the ice melting to see when they had exactly melted. This would improve the accuracy of the experiment. Another improvement would be to carefully measure the water in the ice cube tray for consistent ice cube measurements before they froze. This would increase the validity of the experiment because the ice cubes are of the same size. These improvements would create a far better designed experiment.

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