Temperature - At low temperatures, particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy; so more collisions are successful. Therefore, the rate of reaction increases. This is called the kinetic theory. A reaction goes approximately twice as fast when the temperature is increased by 10 degrees. This is why it is important to keep this variable constant .To do this; I will need to do the experiment on the same day if possible. This ensures that the differences in room temperature, however small, do not affect the rate of reaction.
The factors likely to effect my investigation are:
- Volume of Sodium Thiosulphate
- Volume of Hydrochloric acid.
- Temperature
In my investigation I will change the temperature.
Temperature
- Lower energy therefore particles move slowly so a slow reaction
- More energy therefore particles move faster so more collisions, so faster reaction
- The collision theory explains that increasing temperature makes reactions faster.
Prediction
I predict that the higher the temperature of sodium thiosulphate the faster the reaction will be. I know this because the heat energy will speed up the reactions taking place because heat makes the particles move faster thus more collisions. When the temperature is lowered the opposite occurs because the atoms have less energy and would hit less hard and fast so it would take a longer period of time to get the same result. My prediction of how the graph would look like is this:
The graph begins to go down because at certain temperatures as the atoms get more energy and collide more, making the cross seem to disappear faster. A theory, which links to this experiment, is the collision theory. This is because the collision theory deals with atoms vibrating as they receive more energy and they hit more often.
Diagram
Method
- Measure 10ml of hydrochloric acid into conical flask
- Heat over Bunsen burner until desired heat
- Remove immediately when desired temperature is reached
- Add 25ml of Sodium thiosulphate
- Time to see how long the cross takes to disappear completely
- Repeat 3 times
- Rinse and repeat to the heat 10ºC higher than the last temperature
I will begin with 20ºC, as this is closest to room temperature
Fair Test
In order for my results to be valid the experiment must be a fair one.
- The same judgement will be used each time for trying to see when the X has disappeared.
- The same conical flask ill be used each time so the glass at the bottom is the same thickness throughout the experiment
- The measuring cylinders for the HCl and thiosulphate will not be mixed up.
-
The concentration of HCl will be the same each time, and the amount of thiosulphate will be the same. The independent variable is temperature.
- During the heating stage of the experiment, a blue flame will be used throughout.
- The same X will be used
- Keep stirring the same
- Consistency when starting the stop clock, start it at the sane time for each test
All of these precautions will make my final results more reliable and avoid any abnormalities and anomalous results. The only change that will happen will be that the temperature of the solution will go up.
Safety
- A pair of goggles will be worn during the heating part of the experiment in order to protect the eyes.
- When handling hot beakers and measuring cylinders a pair of tongs will be used.
- A gauze and heatproof mat will be used while heating to avoid any damage to the equipment.
-
Extra care will be taken when using the substances as HCl is an acid and Sodium thiosulphate is poisonous.
Results
Observations
From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower temperatures to the higher temperatures. Having plotted my rough 1st draft of my graph I found that my results were reliable and accurate. I had two anomalous results even after an average over three measurements. These were at 25°C and 30°C. This is because when plotting my graph all of my results fitted on a curved line all except one; this is the odd one out because it does not fit on the curved line. I think may have been because when we rinsed the beaker out water may have stayed in causing the reaction to slow down, I also found it quite hard to spot where the exact moment when the cross disappeared. This is why we did the average over three measurements.
This is my retesting results table
I can say that looking at my repeated results, they were quite close together.
I then plotted them on a graph with my other results. This fitted on a curved line. The higher the temperature the less time the reaction takes to happen. As the temperature is higher there is more energy so therefore the particles move faster and faster. Reactions happen if the particles collide with enough energy. At a higher temperature there will be more particles colliding with enough energy to make the reaction happen.
In my experiment I expect trend to be for every 10 raise in temperature the rate of reaction to double.
Actual difference- because these number aren’t the same the trend is not directly the same, so therefore my prediction for these results of the experiment were not correct.
Expected results ½ first one- closer to time of reaction doubling for every 10.
The higher the temperature the more particles moving faster therefore there is more collisions plus the collisions are more likely to result in a reaction.
When I was carrying out my experiment I made sure that I followed the method correctly and also considered the safety of my experiment. I also carried out everything to make sure it was a fair test. I know I followed this correctly because of my results in the way that none of the different temperatures don’t overlap in time wise After my experiment I have found out that the hotter the hydrochloric acid the faster it takes for the cross to disappear. When the hydrochloric acid and the sodium thiosulphate were clear and see thorough but when mixed they turned a yellow cloudy substance this was due to the sulphur released. This shows that my results were correct.
My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at room temperature, the time for the cross to disappear was 88.7 seconds and at 70°C the time for the cross to disappear was 10.1 seconds, a difference of nearly 80 seconds. The particles were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose.
I think the experiment was successful. I might have been able to improve my results by using more finely tuned equipment or repeating the experiment more times. I encountered 1 anomaly in my results, and this may be explained by the only drawback in the result accuracy: human error when operating the stopwatch.
To improve the experiment I would need to have a very accurate stopwatch to time exactly how long the cross took to disappear so I could be really precise in my results. Ways in which I could extend this experiment are to use a different size of cross so that it doesn't disappear at such a low temperature this way I could carry on to see whether the collision theory is still right at higher temperatures. I feel I could do more to expand on the original question set by perhaps doing other experiments linking with this one like looking at for example:
·Concentration,
·Pressure,
·A catalyst.
I may have been able to study concentration; the more concentrated a product is the more particles there are to react in the same volume. Therefore, the products will collide more and react faster. Pressure will cause the particles to be forced closer together and therefore react faster. Finally, a catalyst will increase the rate of reaction by making the products react quicker while not reacting or breaking down itself. This can be very useful as it can be used over and over again.
