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Patterns Of Chemical Change

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Aim: - To see how the concentration of a reactant (Hydrochloric Acid) affects the speed of a reaction. Introduction Preliminary Experiment: Method: 1. First measure out 50cm� of one molar HCl. 2. Then put 25cm� of Sodium Thio Sulphate into a measuring cylinder as well. 3. Then pour the two solutions into a single beaker. 4. Time this reaction. 5. Then after this measure out 25cm� of HCl and 25cm� of 'distilled' water. 6. Repeat step '2' 7. Then pour the water, HCl and Sodium Thio Sulphate into a single beaker and time this reaction also. 8. Then repeat these 7 steps for the two and three molar acid. Results: Sodium Thio Sulphate Distilled Water HCl (1 Molar) Time (Mins) 25cm� 0cm� 50cm� 01:25 25cm� 25cm� 25cm� 01:34 Sodium Thio Sulphate Distilled Water HCl (2 Molar) Time (Mins) 25cm� 0cm� 50cm� 01:18 25cm� 25cm� 25cm� 01:14 Sodium Thio Sulphate Distilled Water HCl (3 Molar) Time (Mins) 25cm� 0cm� 50cm� 01:16 25cm� 25cm� 25cm� 01:13 In the preliminary experiment I tested different molar (concentration) of acid, one with just HC acid and a second one with half distilled water and half HCl acid. I did this to give me a general gist of how my real experiments would go and to help me with my hypothesis on how concentration affects the rates of reaction. ...read more.


Now let's consider the example with reactant with 70% concentration, the probability of collision is 7/10 while a reactant with 100% concentration has a 10/10 probability of collision however this may be lower than this and the rate of effective collision is most likely lower than that. Also the 100% concentrate reactant is 1.4 times more likely to collide than the 70% concentrate. While the 60% is twice as likely to collide as the 30% concentrate, I believe these probabilities are why there is such a different in reaction times of 30% concentrate and 60% concentrate, on the other hand there is a small difference between the reaction times of 70% concentrate and 100% concentrate. (Note: These numbers are merely hypothetical and were inspired by the results from the preliminary test and when I refer to the concentration values like this e.g. lower bound of concentration I am merely hypothesising using values from the preliminary experiment.) Variables: The concentration of the acid in this experiment shall be changed but the amount of Sodium Thio Sulphate shall remain the same. Also the HCl will always be two molar. Method:- 1) Put 50cm� of Hydrochloric Acid into a measuring cylinder. 2) Afterwards measure out 25cm� of Sodium Thiosulphate into a measuring cylinder (watch out for cross contamination make sure that you find a way to distinguish between the two.) ...read more.


These results partially back my hypothesis, as we can see between 30% HCl and 10% HCl concentrate there is a 32 second difference, while the difference between 70% concentrate and 100% concentrate is only 10 seconds. More extensive experiments would be needed to determine whether there is some truth to my hypothesis. However it seems my first prediction was true; there is a general trend in my results. The reaction time increases as the concentration decreases. However there are still a few anomalies within the results. Evaluation:- The experiments conducted had few mistakes and have been identified. The mistakes have not had a great overall effect on the results except in some cases. To improve results it would be best to have the same person timing THROUGHOUT the experiment. Also the person watching the reaction must be present at all times during the experiment. No cross contamination could have taken place during the experiment because the conical flask was thoroughly rinsed and dried. If the experiment were to be conducted again these controls will be observed and also the experiment should be conducted 'at least' 5 times. Also it would also be good if we could do the same for one molar HCl and three molar HCl. However everyone wore safety glasses while experiments were conducted and also there was a fair amount of accuracy in the results. Further experiments would need to be conducted to get a more accurate result. ?? ?? ?? ?? Science Coursework - Patterns of chemical change. Mohammed Jubair Jalil 10AJN 05/04/06 ...read more.

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