- This reaction shall take place inside water baths of different temperatures in order to keep the reactions at the desired temperatures. The water baths will consist of a beaker filled with water, which will be heated to the desired temperature using a Bunsen burner and then the temperature of the water bath will be measured using a thermometer
- An ink dot will be marked underneath the water bath so that when the solution becomes opaque the dot will become invisible. The time taken for the dot to become invisible will be measured with a stop clock and recorded. The use of a dot underneath the water bath will make the timing more accurate.
- A conical flask will be used as the reaction vessel as it is easier to see the dot through the conical flask than through a test tube and the conical flask would also be more suitable for being stood up inside the water bath.
- I shall take 5 readings from 30ºC to 50ºC, one each 10ºC, this will give me a wide range of results to analyse.
- To increase the reliability of my results I will take as many repeat readings as time allows.
- To ensure that it will be a fair test I will keep the following things the same: the volume of the Sodium Thiosulphate and Hydrochloric Acid solution, the concentration of the solutions, the size of the conical flask, the amount the reactants are stirred and the method of determining when the solution has become opaque. I shall also use different apparatus for storing the two solutions before the reaction and ensure they do not become contaminated as this could affect my results.
- I shall take precautions regarding safety such as wearing safety goggles for protection, as Hydrochloric Acid is corrosive and irritant. I shall also take care regarding the Bunsen burner used to heat up the water bath, I will use a heatproof mat to protect the work surface and I shall be careful when handling hot equipment.
Prediction
From preliminary work I have done involving changing concentrations of the solutions I found out about collision theory. Collision theory states that in order for a reaction to occur, particles must collide with enough energy and Kinetic theory states that particles move around more when they are at higher temperatures because they have more energy. Therefore the rate of reaction will increase as temperature increases, as more collisions will occur sooner due to the increased movement of the particles. In all reactions there is an energy barrier, which needs to be broken in order for the reaction to occur; this is known as the activation energy. Normally only a small percentage of collisions result in a reaction but if temperature is increased then more of the particles will have enough energy to break the activation energy barrier therefore more of the collisions between particles will be successful so the rate of reaction will increase.
Obtaining
How I Obtained My Results
I obtained my results by putting Sodium Thiosulphate solution and Hydrochloric Acid together in a conical flask and then heating the water bath around the reaction vessel to certain temperatures and measuring how long it took for the solution to become opaque using a stop clock.
1st Set of Results
Repeat Set of Results
Observations
When conducting the experiment I noticed that at a higher temperature the solutions became colourless more quickly. I also noticed that the solutions seemed to become cloudy very rapidly at the start of the reaction yet as the reaction progressed they become more cloudy at a slower rate; this suggests that the reaction takes place more quickly at first and then slows down gradually until one of the reactants is used up.
Analysing
As the formula for rate of reaction is:
Rate of Reaction = Amount of Sulphur Produced
Time
I shall convert all of my results for time taken into
I will then use that to draw a graph and analyse the rates of reaction, as the amount of sulphur produced each time in the reaction remains constant therefore 1 can be substituted into the formula and the graph will still have the same shape and gradient as if the actual amount of sulphur produced was used in the formula.
I shall plot these points onto a graph; I shall plot the points of my first set of results in black ink and my repeat set of results in blue ink. I shall then draw a line of best fit between all of the points, allowing for any anomalies.
When I plotted my graph, it showed that as I had predicted and observed the rate of reaction had increased as the temperature increased- this supports my prediction. This occurred because increasing the temperature of the solutions gave the molecules in the solutions more energy. As the particles had more energy, they moved around faster and therefore more collisions between molecules can occur in an amount of time, increasing the rate of reaction. It also means that more of the particles will have more energy than the activation energy needed for the particles to react so more of the collisions that occur in an amount of time will result in a reaction. This is another reason why the temperature of a reaction affects the rate of reaction.
When working out gradients on my graph I found that the graph was steeper when the temperatures were lower. As the temperatures got higher, the rate of reaction was affected less. This suggests that perhaps there is another factor limiting the rate of reaction at this point. This factor could be the concentration of the Hydrochloric acid or Sodium Thiosulphate solutions.
When observing the reaction, I found that the reaction was much faster at the start of the reaction. This was because as the particles collided and reacted, there were less of the particles of the reactant left in the solution thus decreasing the concentration of the solutions. This made the rate of the reaction decrease.
Evaluating
Some parts of my experiment went well but there was a lot of inaccuracy due to human error. It would have been a lot more accurate if I had used a data logger, which could measure the amount of light that could pass through the solution and then produce a graph on the computer. This would reduce errors and could even eliminate any anomalous results. My results could have been made more reliable by taking another repeat set of results. Unfortunately, due to constraints regarding time, I was unable to do this so my results may not be as reliable as they should be. I could also have made my results more accurate by using more appropriate ways of measuring the substances for example I could have used a burette instead of a measuring cylinder.
If I did the experiment again I could narrow the range of my readings by taking readings every 5ºC instead of every 10ºC. This would enable me to draw a more accurate graph. I could also try to investigate the effects of reactants with larger surface areas or more concentrated solutions. If I was correct in this investigation then these variables should affect the rate of reaction. If magnesium chips were placed in acid, the chips with larger surface areas should react more quickly as more of the particles are able to collide with other particles, causing the rate of reaction to be faster. Higher concentrations of the reactants in solution should also cause an increase in the rate of reaction because there would be more of the particles of the reactant available for colliding; therefore more successful collisions should occur in any period of time.
