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I will be investigating how the rate of reaction changes as the concentration of a solution changes.

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Introduction

Chemistry Coursework Rates of Reaction Aim I will be investigating how the rate of reaction changes as the concentration of a solution changes. I will do some preliminary research and investigations, which will lead to the main part investigation where I will change, the concentration of Sodium Thiosulphate when reacting with Hydrochloric Acid (See Method). I will analyse and evaluate my results and look for relationships and trends in them, I will also be considering any anomalous data. Scientific Information Rates of reaction can be increased (according to the collision theory [see Collision Theory]) in four ways: 1) Higher Temperature increases the number of collisions. When the temperature is increased the colliding molecules all move faster so they are going to have more collisions. (Faster collisions increase the rate of reaction.) So more of the collisions are also more energetic and exceed the activation energy for reactions. Reactions can only happen when different particles come together. 2) Increase in Concentration (or Pressure) increases the number of collisions. When there are more particles around to take part in a chemical reaction, they bump into each other more often, which make collisions between the important particles more likely. In a gas increasing the pressure means the molecules are more squashed up together so there are going to be more collisions. 3) Increase in Surface area increases collisions. If one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area so collisions are far more frequent. Due to more collisions the rate of reaction is greater. 4) Catalysts are important for many biochemical and industrial processes because they speed up reactions that ordinarily occur too slowly to be useful (catalysts don't get used up them selves). There are different opinions to the reason to why this happens: i) A catalyst works by giving the reacting particles a surface to where they can bump into each other. ...read more.

Middle

Add both Sodium Thiosulphate and Hydrochloric Acid to the conical flask and start timing. 6. Stop timing when cross becomes obscured (viewing from above of the conical flask [birds eye-view]) 7. Wash the conical flask with water so any chemicals will not remain and repeat experiment by changing the concentration of the Sodium Thiosulphate at each interval (see table or different concentrations). Amount of Sodium Amount of Time taken for X to be obscured (mins/secs) Thiosulphate (ml) Water (ml) 1st set of results 2nd set of results 3rd set of results Average results 50 0 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 45 5 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 40 10 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 35 15 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 30 20 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 25 25 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 20 30 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 15 35 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 10 40 __mins __ secs __mins __ secs __mins __ secs __mins __ secs 5 45 __mins __ secs __mins __ secs __mins __ secs __mins __ secs Results Table (Obtaining Evidence) After performing the experiment I recorded my results on the following results in the table. Amount of Sodium Amount of Time taken for X to be obscured (mins/secs) Thiosulphate (ml) Water (ml) 1st set of results 2nd set of results 3rd set of results Average results 50 0 00 mins 47 secs 00 mins 50 secs 00 mins 45 secs 00 mins 47 secs 45 5 00 mins 56 secs 00 mins 51 secs 00 mins 58 secs 00 mins 55 secs 40 10 01 mins 08 secs 01 mins 11 secs 01 mins 03 secs 01 ...read more.

Conclusion

Only two measurements were used to calculate the average for that interval which would reduce the accuracy of that interval but would not affect the credibility of the whole experiment. I did observe and conceder the meniscus that was present on each liquid, to overcome this and to make measurements more accurate I placed the measuring cylinder with the liquid inside on a flat bench and looked at it at eye level. I decided to reduce the concentration of Sodium Thiosulphate by 5 ml at each interval instead of 10 ml to show in further details, any trends and relationships. Using the results I constructed two tables (results table and relationship table) and a line graph, (look at graph and tables). The initial concentration for Sodium Thiosulphate was 0.1 mole, which was gradually reduced using water. The initial concentration for the Hydrochloric Acid was 0.5 moles, which remained constant throughout the experiment. I did not observe any specific anomalous data in my results. The massive time increase between the last two calculations (Sodium Thiosulphate 5 ml, Water 45 ml) can be acceptable because of the extremely low concentration of Sodium Thiosulphate. In my opinion I think that the graph should have looked more smother; this may be due to the overall accuracy of the method used or any limitations. I would recommend changes by: > Conducting a preliminary investigation to observe and find out if any gasses are released during the course of the experiment, if so then another experiment could be conducted and the results of both experiments compared. > Calculating the concentration of the solutions, much more accurate results. > The Water, Sodium Thiosulphate and Hydrochloric Acid could have been weighed; this would be very simple and more accurate then using the measuring cylinders. > Temperature could have been measured after each reaction to see if any heat had been given off. Chemistry Coursework 1 Mizanul Hoque (3884) ...read more.

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