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# Investigate the rate of reaction between sodium thiosulphate and hydrochloric acid, when you change the concentration

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Introduction

Antoine Allen Investigate the rate of reaction between sodium thiosulphate and hydrochloric acid, when you change the concentration Aim The aim of this experiment is to investigate what affects the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. By using the bariable of sodium thiosulphate concentration Equations Na2S2O3 + 2HCl = 2NaCl +SO2 H2O + S Sodium thiosulphate + hydrochloric acid = Sodium Chloride + sulpur dioxide + water + sulpur Background research What is the most accurate way of obtaining the reaction rate between sodium thiosulphate and hydrochloric acid? The average rate of a chemical reaction, over a certain time, is equal to the change in concentration of the reactant or the product divided by the time taken. Which method you use depends on the type of reaction it is. One way of finding this out is by carrying the reaction out in a thermostatically controlled bath - i.e. one that you can control the temperature of. A sample of the reacting mixture is withdrawn with a pipette and the reaction within this bit of the mixture is stopped. This can be done in a number of ways like removing one of the reagents or suddenly cooling the mixture. You then perform a titration to find the concentration of one of the reactants or one of the products. If you do this at regular intervals, you can determine the rate at which the reaction is happening. In a reaction where a gas is formed, you have to use a different method. The volume of gas must be recorded at various times. The rate of a reaction is defined as the speed at which the reaction takes place. Most molecular collisions do not result in chemical change. Before any change takes place on collision, the colliding molecules must have a minimum kinetic energy called the Activation Energy. This is shown on the energy level diagrams below. ...read more.

Middle

My scientific reason for this is 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. The higher the concentration the more collision per second. This will also increase the rate of reaction. Fair test To make this experiment a fair test, we need to make sure we do a number of things. In this experiment we are trying to find the rate of reaction using concentration as a factor, so there is a number of things we need to make sure we do to keep it a fair test. Firstly, we need to keep a chemical at a constant concentration. Therefore, in this experiment we have chose to keep hydrochloric acid at a constant concentration. We could have, however, used sodium thiosulphate as a constant, but we had chose to use hydrochloric acid. Next, we must make sure that the solution is kept at a constant volume throughout the experiment. If the volume is different, then it could give different results to if it was at a constant volume. We must also make sure that we add both the water and the sodium thiosulphate at exactly the same time (into the conical flask with the hydrochloric acid in it), or it could effect the results of the experiment. ...read more.

Conclusion

Measurements that are more accurate could have been used as the measuring cylinders used were only to either every 0.5cm2 or 1cm2. This is not very accurate. To help make this experiment more accurate, I repeated it two times and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables except for the concentration of sodium thiosulphate the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example: b) It is also impossible to precisely measure out the amounts of Hydrochloric acid, sodium thiosulphate, and Water each time. As the scale on the pipettes shows the volume to the nearest mm3 the volume of the solutions that I used should be correct to the nearest mm3. The volume of gas in the test tube to start with is slightly affected by the amount which the bung is pushed down each time, if the bung is pushed down further then the volume in the tube will be less and the gas will reach faster. c) Due to the slow speed of our reactions, it is only possible to measure the time of the reaction to the nearest 0.1-second although the stopwatch shows the measurements to the nearest 0.01 second Improvements I have stated many the improvements in my evaluation. You could use pipettes to a high degree of accuracy Alternatively, you could change the layout of the experiment as it shows in his diagram. You could have a light bulb and a light sensor then you would no exactly when the reaction had got to the point where you can no longer see through it. Extend I could extend the experiment by having bigger quantities of the solution. On the other hand, I could change the variable. Alternatively, I could put the experiment into a water bath and see if keeping the temperature the same changes the out come of the experiment. ...read more.

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