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An investigation into the effect of concentration on the rate of reaction.

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An investigation into the effect of concentration on the rate of reaction I-Planning I will carryout an experiment that shows how the rate of the reaction* is affected by the concentration of one of the reactants. *The rate of the reaction is the rate of formation of a product during a chemical reaction or it is the amount of reaction which occur in a unit time. AIM : I will investigate the effect of different concentrations on the rate of a reaction. I chose the reaction between sodium thiosulphate and hydrochloric acid. I will observe the time taken for each reaction to complete (i.e. for the yellow ppt.of sulpher to form ) EQUATION OF THE REACTION : WORD EQUATION : Sodium thiosulphate + hydrochloric acid sodium chloride+ water+sulphur dioxide gas+sulphur. SYMBOLIC EQUATION : Na2S2O3 + 2HCl 2NaCl + H2O + SO2 (g) + S (s) FAIR TEST : In order to obtain the most accurate results and have a controlled experiment I have to control the variables so I will plan a fair test; CONSTANT FACTORS : 1- Room temperature pressure. 2- Not to use a catalyst. 3- Same light intensity. 4- The concentration of hydrochloric acid (2 mole ) and volume (5 cm3). ...read more.


add 5cm3 HCL solution using a pipette. Immediately start the stopwatch . 4. A precipitate of sulphur (pale yellow ) will appear , deposits at the bottom of the conical flask observing the cross gradually 5. when the cross is completely covered with the yellow precipitate stop the stopwatch and record the time taken for the cross to obscure . 6. Repeat the experiment again using the different conc. Of sodium thiosulphate and the same concentration and volume of hydrochloric acid . THE DIAGRAM SHOWS THE SULPHUR PRECIPITATES IN MY EXPERIMENT : Conical flask White paper At the start of the reaction before the formation of sulphur. After a while sulphur appears but does not obscure the cross completely. after the reaction is complete, the cross is no longer visible. REPETITION OF THE EXPERIMENT : I have repeat my experiment using 5 concentrations at a time at last twice . for more accuracy and a trial to reduce the human error , I will repeat my experiment three times taking the average between them . SAFETY AND PRECAUTIONS : 1- handle the acid with care and responsibility because it is corrosive and might hurt the skin. 2- Make sure glass objects cannot roll off the tables and also make sure that they do not have cracks. ...read more.


IV- EVALUATING EVIDENCE I think that my results and evidence are quite sufficient that if anyone else repeats my experiment should have a conclusion like mine. He should conclude that the more the concentrated the solution is, the faster the rate of the reaction is. All the variables in my experiment are easy t control and possible to measure that I did not find any difficulty in controlling the variables. I think that my results are quite reliable because it goes with my scientific knowledge and predictions. Some improvements such as the following could be applied to improve the accuracy of my procedure; - I might repeat the experiment one more time although three times are quite sufficient but my results would be more accurate if I do more repeats. - I prepared the concentrations using a measuring cylinder but it would be more accurate if I use titration. - I might improve the accuracy of my experiment by trying more in-between concentrations to get a bigger range of results. A bigger range of results would improve the averages and will fill some gaps in the graphs. further investigations that may elongate my own experiment are like: I may investigate the effect of other variables on the rate of the reaction e.g. temperature, catalyst, surface area or pressure. I may also use other reactants to observe the effect of concentration on the rate of reaction ...read more.

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