Method:
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Collect Apparatus (10cm³ Measuring cylinder [Acid Only], Small Beaker [Acid only also] 50cm³ Beaker [Thiosulphate & Distilled Water Mixture], Large Beaker, Conical Flask, Filter paper with “X” marked on it, Safety Goggles, Stopwatch and a sheet to record results)
- Collect 200cm³ of Thiosulphate into Large Beaker from Winchester flask.
- Put 50cm³ of Sodium Thiosulphate into the 50cm³ beaker.
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Mark “X” on the filter paper and place the Conical flask on top of it.
- Put approximately 30cm³ of Hydrochloric acid into the small beaker, and then pour 10cm³ into the small measuring cylinder.
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Pour the acid and Thiosulphate into the conical flask, swirl once and start the stopwatch at the same time, place the flask back onto the “X” paper and observe until the “X” disappears.
- Record time and empty the contents of the conical flask into a big bowl and wash the flask.
- Repeat above steps but this time use 45cm³ of Thiosulphate diluted with 5cm³ of distilled water.
- Repeat for other dilutions of Sodium Thiosulphate
Results Table:
I originally planned to do each experiment 3 times, but due to the shortage of time I was limited to only repeating each experiment twice. In the column labelled Experiment 2 I have highlighted my 3rd reading in Red because it seemed unusual to me. I repeated the experiment a third time and got 25 seconds. I was content with this result because it was closer to my first reading. I also highlighted my 6th reading in bright green, because this also seemed unusual, after repeating this experiment I got a result of 43 seconds. This was also more accurate and therefore I was happy. My final result has a very big difference (29 Seconds) and is not accurate; I did not repeat this particular experiment, again because of the shortage of time.
I have decided to draw a line graph in order to present my results statistically.
Collision Theory
For a reaction to occur, 2 things must happen:
- The reactants must collide
- The reactants must collide with sufficient energy in order to react i.e. making a successful collision.
For the reaction between hydrochloric acid and sodium Thiosulphate both the reactants are aqueous solutions and therefore in the liquid phase.
The particles in a liquid are able to move past each other although the particles are much close together than those in a gas.
= Hydrochloric Acid = Sodium Thiosulphate
In this experiment I have found that as the concentration is increased the time taken for the reaction to take place decreases. This means the rate of reaction increasers as it takes less time for a reaction to take place, so more take place per second. Using the graphs, I can draw a conclusion from my experiment. Firstly I can see that with the “time” graph (that plot concentration against time taken for the reaction to take place) the graphs have negative correlation in both cases, meaning that as the concentration increased the time taken for the reaction to take place decreases.
For this to fully make sense it is necessary to recap the collision theory briefly:
For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area.
