I predict that the more Ammonium chloride that is used the lower the temperature will become, the waters energy is used to break bonds when Ammonium chloride is added, because the energy is being taken from the water and not as much is given back making the reaction endothermic therefore the water temperature will drop. I also predict that the temperature will come to a point where it doesn’t get any cooled this is because the mixture becomes saturated.
The idea of this experiment is to find out how the amount of ammonium chloride affects the temp change. I will do this by doing a number of the same experiment using different amounts of Ammonium chloride and measuring the temp change.
Too keep the tests fair I will use the same amount of water in each experiment (50cm3), check temperature at regular intervals (20 seconds), and stir the water to the same extent.
Accurate and reliable
I will do the experiment three times and calculate an average to get a good set of results. I will make the experiment reliable by keeping all the variables identical (excluding those being tested).
This is the method to do the experiment.
1. Measure 50cm3 of water using measuring cylinder.
2. Put the water into a polystyrene cup.
3. Use weighing equipment to weigh required mass.
4. Record the starting temperature of the water
5. Add Ammonium chloride to water, stir (keep stirring) and take the temperature every 20 seconds.
6. Record he max temperature drop
7. Repeat 2 more times using the same mass of Ammonium chloride.
8. Calculate average temperature using this formula: –
((1st result + 2nd result + 3rd result) / 3) = average
9. Repeat steps 1-9 with next mass on list until all required mass have been completed.
Conclusion and interpretations
I have discovered that the more Ammonium chloride that is added to the water the cooler it gets until it starts to level off at a 12?C drop.
I got the results that I predicted.
I understand that the temperature will drop until a certain point where it levels off at a max temperature drop of 12?C. I think it levels of at 12?C because I the mixture becomes saturated, meaning that the energy in the water is no longer efficient to break and more bonds hence making the water cooler. The water runs out of energy because the reaction is endothermic meaning that more energy is used to break bonds than is given back when bonds are created therefore all the energy will eventually be used.
I think my results are accurate because of the neatly formed curve on the graph and the fact that they where measure to 2dp, there where however two results there were obviously inaccurate because they seemed to be far from the line of the graph (sometimes called intrinsic errors), therefore I have omitted those results. There are several factors that could be making the results inaccurate; those factors follow:
* Because the different masses were done by different groups in the class to save time, some people may not have stirred the mixture as much as others.
* Others may have used a slightly different amount of water by mistake.
The inaccurate results could be repeated but the environment might not be reproduced correctly (for example the ambient temperature), if the tests where repeated then extra precautions must be taken to ensure that the tests are fair.
My results in my opinion are reliable because none of the results are obviously inaccurate besides the one I pointed out above. I can tell that they are reliable because the 3 results that where used to make an average where often the same. The same reasons as above would be the most like to be making the results unreliable as well. Again the unreliable results could be re-done but some of the factors like ambient temperature might not be reproduced properly.
My results support my conclusion by showing that the temperature does actually drop to a point where there isn’t enough energy to break and more bonds or until it becomes saturated. This is also what I predicted which has been proved to be correct.
I could improve this experiment by doing all the experiments myself to make sure that all the variable where keep equal (bar the ones being tested), I could also do the experiments more that three time, because the more results you have the better your average will become.
Further research could be done by studying the properties of Ammonium chloride, to find out more about why more energy is need to break bond than is given off when bonds are made. Most of this research would be available online.