Equipment:
Safety Goggles
Gloves
1M Sodium Thiosulphate Solution
0.5M Hydrochloric Acid
100cm3 Conical Flask
2 x 50cm3 Plastic Measuring Cylinder
2 x 50cm3 Glass Measuring Beaker
Stop Clock
White Sheet of Paper with a Cross in the centre
Labels
Method:
Firstly for the different concentrations of Sodium Thiosulphate solution I manually diluted it. To do this I had 100cm3 of the 2 Molar Sodium Thiosulphate. I poured one half of this into a separate beaker and added 50cm3 of water to the second beaker. So with 100cm3 of 1 Molar Sodium Thiosulphate in the second beaker I poured 50cm3 of that into a third beaker I again added 50cm3 of water to the third beaker and it resulted in a 100cm3 0.5 Molar Sodium Thiosulphate. Finally I added half of the contents of the third beaker to a fourth beaker and added 100cm3 to that beaker to get 100cm3 of 0.25 Molar Thiosulphate.
The Method I will use is;
1. Gather all equipment make sure they are clean and uncontaminated and work efficiently
2. Place equipment as required on the work surface, with the conical flask over the crossed white sheet, and the hydrochloric acid placed at one end of the work area with a plastic measuring cylinder and glass beaker and at the other end with a plastic cylinder and glass beaker the Sodium Thiosulphate Solution. (the beakers and cylinders are not to be mixed)
3. Set the Stop Clock
4. Measure out 15cm3 of 2M thiosulphate solution and pour into conical flask
5. Measure out 15cm3 of dilute hydrochloric acid as it is poured into conical flask start timer.
6. Stop the clock once the cross on the paper is no longer visible.
7. Wash out conical flask dry and redo experiment twice more with the same Molar.
8. Redo experiment again with 1 Molar testing it at least twice, then again at least twice for 0.5 Molar and finally at least twice for 0.25 Molar.
Predictions:
I predict that the higher the molar concentration of the solution the quicker the reaction will take place due to concentration being a factor that can change the rate of reaction. Other factors that affect the rate of reaction apart from the concentration are the surface area, the use of a catalyst, the temperature and the pressure. I believe the concentration to be proportional to the rate of reaction so I also predict that due to the concentration increase resulting in the rate of reaction increasing; my graphs will take on a negative gradient with a slight curve.
I know that this investigation works in the guidelines of the Collision Theory which is, for a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to there being an energy barrier to which they must overcome. The particles that will react after collision are those with enough energy to overcome this energy barrier. In order for the collisions to lead to a reaction a minimum amount of energy is required this is the activation energy. This differs in various reactions. So if the frequency of collisions increases so will the rate of reaction. As I stated earlier other factors that can affect the rate of reaction by increasing the frequency of collisions are, an increase in concentration, temperature, pressure and surface area.
Concentration – If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other.
Pressure - If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and thus the rate of reaction.
Surface Area – If a solid is powdered then there is a greater surface area available for a reaction, compared to the same mass of un-powdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
Temperature – This increases the average speed and energy of the particles leading to two things more collisions per second and this increase in collisions enables the particles to posses the activation energy to result in a reaction.
The increased concentration results in the bonds of the particles breaking and forming new ones and an increase of pressure, this also increases the rate of the reaction. Reactions can only happen when the reactant particles collide, but most collisions are not successful in forming product molecules. The reactant molecules must collide with enough energy to break the original bonds so those new bonds in the product molecules can be formed. All the rate-controlling factors are to do with the frequency of reactant particle collision. What will happen in this experiment is I will add hydrochloric acid to an equal amount of sodium thiosulphate. During the experiment the sodium in the sodium thiosulphate solution will displace the hydrogen, to form sodium chloride solution. Once the solution has become opaque I will know the reaction is complete this is due to a precipitate caused by sulphur which turns the solution cloudy whilst expelling sulphur dioxide. The same number of atoms will be kept throughout the experiment they will just be distributed differently compared to the start of the experiment. The rule for calculating the rate of reaction is;
Rate of reaction = change in amount of substance
time taken for the change to occur
Below are a word and chemical equation of the experiment;
Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + SO2(g) + H2O(l) + S(s)
I know that any increase in concentration during an experiment the rate of reaction will increase due to the likelihood of more collisions between molecules due to their being more of them in the same volume of the solution.
