. I predict that as the concentration of the sodium thiosulphate increases the time taken will decrease. This means that one of the two graphs drawn up in my analysis will have negative correlation, and will probably be curved as the decrease in rate of reaction will not be exactly the same as the concentration is increased. the second graph will have positive correlation because as the concentration increases so should the rate of reaction. This can be justified by relating to the collision theory. When the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are then more likely to occur. All this can be understood better with full understanding of the collision theory itself:
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.
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 unpowdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
The particles in a gas undergo random collisions in which energy is transferred between the colliding particles. As a result there will be particles with differing energies.
Using my preliminary experiments I decided on using the following apparatus:
- 2 beakers
- 2 measuring cylinders
- X paper
- Top pan balance
- Stopwatch
- Heat-proof mat
- Pair of goggles
Prediction.
I predict that as the concentration of the sodium thiosulphate increases the rate of reaction will increase. This means that the graph for concentration against rate of reaction drawn up in my analysis will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased, probably because as the experiment continues the reactants will begin to run out. This can be justified by relating to the collision theory. When the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully. If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself:
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.
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 unpowdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas.
The particles in a gas undergo random collisions in which energy is transferred between the colliding particles. As a result there will be particles with differing energies. Maxwell-Boltzmann energy distribution curves show the distribution of the energies of the particles in a gas.
Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + S(s) + SO2(g)
sodium thiosulphate hydrochloric acid sodium chloride sulphur sulphur
Solution solution dioxide
0.5 M
The experiment.
As you can see the reaction creates sodium chloride solution (saltwater) and sulphur which makes the solution cloudy, a gas sulphur dioxide is also released. Hydrogen gas also is released and the two together make an unpleasant smell.
Everyday uses.
Sodium thiosulphate is often used for the analyses of oxidising substances ( for example iodine, hypo chlorite, peroxide). It is also used in hair products, Sodium thiosulphate should not burn your scalp. It is used to relax hair so that it can be fixed into a new shape, such as a permanent wave. It does this by breaking the hair's disulfide (S-S) bonds so that they can be re-formed later to hold the new shape in place.
Observations.
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 increases as it takes less time for a reaction to take place, so more take place per second.
Using the graphs, with lines of best fit, I can draw a conclusion from my experiment. Firstly I can see that with the “time” graph (that plots concentration against time taken for the reaction to take place) the graph has negative correlation, meaning that as concentration increased the time taken for the reaction to take place decreases.
Naturally, the above means that the graph plotting rate against concentration has positive correlation – as the concentration is increased so does the rate of reaction. This is because when solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur.
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.
Evaluation.
The experiment went very well, I collected accurate results thanks to controlling the variables. However there were a few wayward results in my graph, which didn’t really affect the results thanks to doing two experiments for each concentration and then taking an average time. The anomalies are probably due to human error as it is hard to tell weather you can still see the cross or not, this small problem could be solved by using a light sensor to detect a beam of light shone into the solution, this would also improve the accuracy of my results. My prediction was correct, because of my careful research into the collision theory.
I also could of done a second experiment for temperature, and made a graph plotting temp against reaction time, I think that the graph would have negative correlation, I think that as the temp goes up the reaction time will go down. I could also do the original experiment again to get more accurate results by comparing the two sets of results to see if there are any odd results.
