The purpose of this experiment is to see how the concentration of hydrochloric acid affects the rate of reaction when mixed with sodium thiosulphate.

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Terry Cave 10.8

Ms. Cheung

Chemistry Coursework

Candidate Number: 1054

Friday 28th November

Chemistry Coursework

Aim

  The purpose of this experiment is to see how the concentration of     hydrochloric acid affects the rate of reaction when mixed with sodium thiosulphate.

Introduction

  I have been assigned the task of recording, and understanding how the concentration of acids affects their rate of reaction. The experiment will be conducted under the rules of a fair test and will involve mixing sodium thiosulphate with different concentrations of hydrochloric acid. The solution, stored in a beaker, would then be placed above a light sensor, which would then record the amount of light passing through the solution. Once the light sensor takes a final, definite reading this indicates that the reaction has finished. I then have to record the time, in which the solution turns misty restricting light from reaching the sensor and also record the percentage of light reaching the sensor as well. In my coursework I should include:

  • How the preliminary experiment is done, and the results recorded.
  • Give a detailed prediction.
  • List all the appropriate materials used.
  • Write out a step-to-step method of how to conduct the experiment.
  • Include an analysis with graphs and explanations to results.
  • An evaluation with links to defaults in methods, results.

Conducting a Fair and Safe Test

The most essential precautions to achieving accurate results is in making sure that the experiment is a fair test, with all the variables thought of. I will make my results accurate by making sure that the solutions are measured correctly and the same amount is used of each. I will also do a number of trails to obtain an average, that way my results will be as accurate as possible.

The independent variable (what I’m changing) in my experiment is the concentration of hydrochloric acid. The concentrations used will be 0.25, 0.5, 1.0, 1.25, 1.5, 2.0 and will be measured in molars (M). I have chosen these concentrations, as they are as close as possible and will therefore show results in greater detail and also if any anomalies arise, they can be located, as they will differ from the trend of results. Also each concentration will be conducted in two trials to gain an average, as this average will give truer results. I will change the concentration of the hydrochloric acid, as this change in concentration will show how concentration affects the rate of reaction.

The controlled variable (things that are kept the same) will be the amount of both hydrochloric acid and sodium thiosulphate solutions, temperature, and starting light intensity. I will maintain the same amount of both hydrochloric acid and sodium thiosulphate by measuring this amount, each time, in separate measuring cylinders before the experiment is conducted. I will do this as I know how the amount of a solution affects rate of reaction as the more of a solution the more of the solutions particles, therefore this increase in particles in a mixture will determine the rate of reaction. I will maintain the same temperature by allowing the thermometer to go to original room temperature each time before experiments. I will make sure the thermometer is not in direct light, therefore affecting the reading. I will do this as temperature affects rate of reaction. It does this by passing kinetic energy on to the solutions particles making them more active and increasing the amount of hard, fast, collisions in the reacting solutions. I will keep starting light intensity the same as if the reading differs it will be impossible to determine if the reaction as finishes therefore the final reading wont be accurate. Also the light reading is to determine is the reaction has finished and faults in the results would lead to faulty rate of reaction calculations. I will keep starting light intensity the same by making sure the same amount of lights are turned on in the room constantly and by making sure that nothing shadows the light reading device. I have done this as a differ in light intensity will affect the results as this is how I will determine if the reaction has finished.

  Finally the last variable will be the dependent variable (what your measuring), which is how long it takes for the solution to become cloudy and how much light reaches the sensor at the start also I will be monitoring the temperature. I will measure reaction time in seconds and will do so by using a stop clock. I will add the two solutions at the same time and as soon as this is done I will start the clock. As this will ensure that there is no time unrecorded as if there was this could mean the solutions reacting with out even knowing it which would falter the overall results. I will measure end light intensity by using a light sensor and the reading will be calculated by waiting until the sensor takes a final reading of a decrease of 10%. I will do this as light will affect the results, as this is how we will determine if the reaction has finished.

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  Precautions I will be undertaking in my experiment to maintain safety of myself and others include:

  • Wearing goggles at all times.
  • Wearing an apron at all times.
  • Stand up whilst the experiment is conducted.
  • No disruptive and dangerous behaviour in the room.
  • No deliberate spillage of acids.
  • Take care when handling chemicals and equipment.

Prediction

From my preliminary experiment I was able to see that the more concentrated the solution of hydrochloric acid the quicker it takes for the cross to disappear. The results I gained were not great. I feel this was due to the ...

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