Three additional things that affect the rate of diffusion of the ammonia include molecular size, temperature and the concentration of the ammonia. My investigation is aimed at discovering the effects of doubling the strength (concentration) of ammonia on the rate of diffusion. I think increasing the concentration of ammonia will decrease the amount of time it will take for the litmus paper to turn blue i.e. diffusion will be faster. However, decreasing the concentration of ammonia will increase the amount of time it will take for the litmus paper to turn blue i.e. diffusion will be slower. Doubling the strength of ammonia could have an effect on the rate of diffusion because it doubles the number of molecules, which collide more. Consequently, the particles in a gas will spread out and thus have greater space to move around more quickly and easily. This is how ammonia particles will look in the form of a gas as they collide and spread:
To make this investigation a fair test, I am going to space out the litmus papers but not too far apart and evenly spread out each of the seven litmus papers I intend to use. I will also use the same volume of ammonia to make it a fair test each time. The concentration will, however, gradually be doubled. I will start with 0.5% double it to 1%, 2% and finally 4%.
To carry out this experiment using a stopwatch to measure how long it takes for each red litmus paper to turn blue. I will take 1 reading every time a litmus paper changes colour, which will result in 7 readings for every test. Then I will obtain the results taken by two other people in my team and average them out by adding the results up and dividing by 3. This will give me a reliable answer as to how long it took for each of the seven litmus papers to turn from red to blue. So the number of tests to be performed in total is 3 and so by multiplying 3 with 7 will equal 21 results being taken from 21 litmus papers changing colour. These results will be taken in seconds but I shall convert any that are given in minutes by the stopwatch, into seconds.
OBTAINING EVIDENCE
The table below show my results:
To perform this experiment safely it was necessary that we wore goggles and used tongs to pick up the cotton wool that had ammonia on it.
ANALYSING RESULTS/DRAW CONCLUSION
I have drawn a graph on a piece of graph paper to show the pattern in my results. The pattern shows that as you double the concentration of ammonia, the quicker it takes to change colour from red to blue. This is because, as I had predicted, increasing the concentration also increases the number of molecules, which collide more. Consequently, the ammonia molecules spread out to make greater space to move around more quickly and easily.
EVALUATING
The experiment appears to have been successful as I acted according to my plans and achieved the results I had expected. My results could be improved by carrying out the tests a few more times, in order to achieve more accurate results. I can conclude from my results that doubling the strength of ammonia doubles the rate of its diffusion. A pattern in my results also showed that a as you double the concentration of ammonia, the average time is twice as less. However, this pattern was not apparent when I increased the concentration of ammonia from 0.5% to 1%. On that occasion it seems that the time had reduced by more than just a half. The reduction in time was usually approximately by half, but by drawing a line of best fit through my graph, it can be said that doubling the concentration of ammonia does double the rate of diffusion.
