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To find the factors that affects the rate of reaction between dilute hydrochloric acid and sodium thiosulphate.

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Introduction

An investigation write-up. Aim: to find the factors that affects the rate of reaction between dilute hydrochloric acid and sodium thiosulphate. plan: firstly I will get a container of dilute hydrochloric acid and one container of sodium thiosulphate each measuring 25cm cubed, I will mix the two together and measure how long it takes for them to react. I will do this by placing a piece of paper with an x clearly marked on it underneath the mixing container, then starting from when the reactants are mixed and finishing when the x is no longer visible I will time the reaction. I will make the test fair by using the same x and using different containers (there may still be reactants in the containers afterwards) I will also monitor the room temperature at the start of each reaction. Key factors in the experiment will be the concentration of the thio and the acid but also the volumes used need to be exact, in my collecting of results It will need to contain a result where no acid is used as a comparison for the other results. I will use three different concentrations of hydrochloric acid in my experiments doing two of each that way I can get an average time which will be more "true" than the other results, as I have said earlier I should try and keep the temperature the same for each experiment to make sure the results are all accurate. ...read more.

Middle

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. ...read more.

Conclusion

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. ?? ?? ?? ?? ...read more.

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