Increasing the concentration of a substance is basically increasing the amount of particles in a given volume. For example twice the concentration = twice as many particles. This means greater chance of collision and therefore a faster reaction.
Concentration= MASS
________
VOLUME
Concentration therefore will have a direct effect on my reaction as I will keep the volume constant but vary the mass of the Sodium Thiosulphate.
In conclusion I predict that if I decrease the concentration of Sodium Thiosulphate then the reaction with Hydrochloric acid shall take longer to take place. On a quantitative scale I predict that if the input variable is halved then the outcome variable will be doubled. For example if the concentration is 50% it will take twice as long when at 100%.
Some of this information has been obtained using textbooks.
FAIR TESTING:
- Input Variable: Concentration of Sodium Thiosulphate in the given volume.
- Outcome Variable: The time the reaction takes to happen.
- Controlled Variables: Temperature, total volume of liquid, Number of stirs used.
Preliminary work:
For a pilot investigation I compiled a set of compacted results, as I would have in the real experiment, for means to decide upon an amount of hydrochloric acid that is both safe and good enough to react at a decent speed. It is important to not have to larger amount of hydrochloric acid, as the reaction shall be too vigorous and unsafe.
First I tested 5ml of HCl. I found when testing the more diluted concentrations of Sodium Thiosulphate that the reactions were taking extensive amounts of time to finish. This would have jeopardised my ability to obtain more results in the time allocated. At 10ml the time taken was significantly more reasonable and was still safe. This led me to decide upon this volume of acid to use in the actual experiment.
DIAGRAM:
METHOD:
- We will set up the apparatus as in the diagram above.
- We will draw a black cross on a sheet of A4 paper and place it under the chromical flask so it is only visible when the solution is clear.
- We will fill the chromical flask with the necessary concentration of the Sodium Thiosulphate with the 10ml of HCl (which we found was safe in the preliminary work) to form the controlled volume.
- We start timing when the whole volume is in the chromical flask.
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Stop timing and record the result when the black cross is completely invisible.
- Repeat for all other tested concentrations.
SAFETY:
- As we will be using sulphur dioxide we will place a cotton wool bud in the top of the chromical flask to limit our inhalation.
- We will wear goggles as the hydrochloric acid is an irritant and to prevent from going in our eyes.
- We will wash our hands thoroughly after the investigation.
RESULTS SET 1
RESULTS SET 2
CONCLUSION:
I have found out that if you decrease the concentration of Sodium Thiosulphate within a given volume. This was because of the collision theory.
The collision theory states that before a chemical reaction can take place the atoms, molecules or ions of a substance must collide. The more reactions that take place the faster the reaction. This is because when atoms, molecules or ions in a substance collide speed up the reaction. More collisions allow the substance to react faster. Therefore when changing the concentration in the same amount of substance will mean there will be a greater or less chance of collision when you increase or decrease the concentration of Sodium Thiosulphate respectively.
Increasing the concentration of a substance is basically increasing the amount of particles in a given volume. For example twice the concentration = twice as many particles. This means greater chance of collision and therefore a faster reaction. Reducing this will have an opposite effect.
Evaluation:
There were a few difficulties I encountered in this investigation. The main one was estimating the exact moment that the cross, disappeared. Even through trying to do this from the same point every time it was still a very inaccurate process. Also there was a problem with the Sodium Thiosulphate decomposing due to the experiment having to be separated into two days. We had a slight difficulty controlling the temperature in the investigation. In the first day the sun was shining and the heat was present whereas on the second the weather was dull and therefore less heat.
My results were approximately anomaly free and were about 85% accurate. If I were to do the experiment again I would try to conduct all the results in one day as to limit the rotting of the Sodium Thiosulphate. I could extend my investigation further by I could investigate the effects of increasing the volume, the effect of temperature or the effects of stirring.
Another factor I could choose to measure is the rate of reaction. In this experiment the rate of reaction (Time taken for reaction to take place/change in amount of substance) is the inversely proportional to 1/ time taken. These results would have been more conclusive when these were present as the rate itself could have been examined instead of results.