Plan
For my experiment these are the apparatus i will be using, below
- Measuring cylinders
- Conical flask
- Goggles
- Stopwatch
- Paper with black cross on it
- Sodium Thiosulphate
- Hydrochloric acid
I have chosen this equipment for this particular experiment because I thought it would be most relevant to conduct a correct experiment. I have used the measuring cylinders so that i can measure the thio accuratly, also i used the conical flask to store the thio. The paper with a black cross on was used so i could see when the reaction had stopped, I had goggles to protect my eyes. The sodium Thiosulphate and Hydrochloric acid wee used to conduct the experiment.
Diagram
This diagram shows the paper with an X on it underneath the conical flask with the Thiosulphate measured to (25cm3) stored inside. also in the diagram i have shown the stopwatch a measuring cylinder wit h(5cm) of Hydrochloric acid.
Fair Test
In order to make my experiment a fair test i will have to control the variables. I will make sure the same standerd of vision is used each time for when the X has disapeard. I will make sure that the measuring cylinders for the Hydrochloric acid and thiosulphate will not be mixed up. The amount of Hydrochloric acid will be 5 cm3 each time, and the amount of thiosulphate will be fixed at 25 cm3. All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful.
Range of readings
For my experiment I will be using a range of acids at 0.1, 0.2, 0,5 , 1.0 and 1.5m, this is so i have a wide range of readings. I repeated the experiment five times to get a wide range of results to make the experiment more accurate and fair. This will help me observe my results and plot then on graphs.
Method
5 cm3 of Hydrochloric acid and 25 cm3 of sodium thiosulphate (at varying concentrations are poured out into two measuring cylinders and then poured into a conical flask, which is placed on top of a board marked with letter X. The stopwatch will now be started. When the mixture has turned sufficiently cloudy so that the letter X can no longer be seen the stopwatch will be stopped and the time will be recorded. The experiment is repeated with all the concentrations. The whole procedure is then repeated.
Results
These are my results i collected from my experiment, the table shows all 5 concentrations and the result highlighted in red is an anomaly.
Analysis
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 increasers 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” graphs (that plot concentration against time taken for the reaction to take place) the graph have negative correlation in this case, meaning that as the concentration increased the time taken for the reaction to take place decreases. This is because when the temperature is increased the particles will have more energy and wll then 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, and 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.
The graph for concentration shows that when the concentrations were relatively low the increase of rate was also fairly small (increasing from 0.29 to 0.36 to 0.41 to 01:17 to 01:144). There was then a gradual increase in the difference, and between (0.5 and 0.2) the result nearly doubled from 0.41 to 01:17. This shows that there are far more collisions at a concentration of 0.5 than at 0.2. The results do fit my prediction beacuse i stated that as the consentration of the sodium thiosulphate increases the rate of reaction will increase. So the more concentrated solution, there are more successful collisions so the rate of raction will be faster. My results support my prediction because in my prediction i said the greater the concentration of acid the rate of reaction will be faster. This is beacuse the more molucules there are, the better chance of successful collisions and therefore the reaction will speed up.
This diagram shows a clear image of freely movable electrons moving around and in-between the metal ions and colliding which is causing energy to be released. If the metal is heated, the metal atoms will vibrate more. This means that there is a greater chance of an electron bumping into a metal atom and so the flow of electrons is reduced. I.e. the greater concentration, more collisions.
Evaluation
i think that most of the experiment I have done has been fine, with as little anomalous results as possible. However, there are still a few anomalous results which I will now point out.This is the only anomalous result that I have recorded, in red print on my table shows the anomaly which was 01:09. The result may have turned out anomalous because of basic human error, or maybe because we measured the substances wrong. It may have even been because we did not clean the apparatus properly.Apart from this, the accuracy of my experiment has been more or less accurate. Although there are a number of ways in which we could have made the results more reliable. For instance, we could have used better measuring equipment, because the apparatus we used was mainly basic equipment. Even though the experiment went well it was hard to tell when the cross had disapeard, so instaed we could of used a light beam and when that goes out, then that means the process has finished. The average still fitted the prediction even though there was an odd result. Another thing we could have done to bring more evidence is to have tried to use the hydrochloric acid as the variable substance, and used the sodium thiosulphate as the constant substance. This would have brought more evidence to support the idea that the higher concentration of a substance, the faster it will react. I think that the evidence, which I have received, is enough to reach a suitable conclusion, but there are a few anomaly's to the experiment (which I have mentioned). Apart from them, the experiment is fine.
By Ricky Goldblatt Science Chemistry Coursework